Corneal Surgery






Definition


Corneal procedures performed to either restore vision or restore globe integrity.




Key Features





  • Careful preoperative preparation and planning are critical to success.



  • Understand intraoperative and postoperative complications and management.





Associated Feature





  • Be alert to the signs and symptoms of graft rejection.





Keratoplasty


Introduction


The successful outcomes enjoyed by patients who undergo modern penetrating keratoplasty (PKP) and lamellar keratoplasty are the result of advances in technology and surgical techniques.


Historical Review


Corneal grafting techniques were pioneered by ophthalmologists, such as Reisinger, von Hippel, and Elschnig. Today keratoplasty is the most common and successful human transplantation procedure, with over 45 000 corneal transplantations performed in the United States each year. The number of PKP decreased to less than 20 000 in the year 2014, and the number of endothelial keratoplasty (EKP) increased to over 25 000 in that same year. Optical results have improved significantly as a consequence of advances in tissue selection and preservation, techniques, trephines, and management of postoperative astigmatism.


Lamellar grafts date back to 1886 when von Hippel successfully performed the first lamellar grafting in a human. Lamellar techniques have revolutionized the treatment of corneal diseases by offering such advantages as faster visual recovery, less postoperative astigmatism, and decreased risk of suture-related complications compared with PKP. Because “selective keratoplasty” replaces only the diseased tissue, the risk of graft rejection is theoretically lower. EKP now has become the standard of care for endothelial diseases.


Anesthesia


Corneal transplantation may be performed under cover of regional or general anesthesia, depending on patient preference and cooperation. Typically, local anesthesia entails peribulbar or retrobulbar injection of lidocaine 2%, bupivacaine 0.75%, and hyaluronidase. A lid block may be employed to prevent squeezing.


Specific Techniques


Penetrating Keratoplasty


PKP involves full-thickness replacement of corneal tissue with a healthy donor graft.


Preoperative Evaluation and Diagnostic Approach


PKP may be used to provide tectonic support (as in corneal thinning or perforation) and to improve visual outcomes (as in the replacement of an opaque or irregular cornea). Indications for PKP include keratoconus; previous graft failure or rejection; full-thickness or deep corneal scars; Fuchs’ endothelial dystrophy; pseudo-phakic or aphakic bullous keratopathy; chemical burn; corneal ulcer; corneal dystrophy and degeneration; herpetic keratitis; trauma; or any other causes of corneal decompensation. Conditions with primarily posterior pathologies, such as Fuchs’ endothelial dystrophy and pseudo-phakic or aphakic bullous keratopathy, now are commonly treated with EKP. The rate of success of PKP is excellent, but the long-term risk of graft rejection increases significantly with active or recurrent infection, inflammation, corneal neovascularization, previous graft rejection, and each subsequent penetrating graft.


It is important to perform a careful preoperative evaluation and have a thorough discussion with patients about the surgery, visual expectation, possible complications, and the long postoperative course. The recipient must be prepared for the lifelong care required. In general, important considerations for the preoperative evaluation for PKP are as follows:




  • Visual potential must be evaluated.



  • Ocular surface must be optimized before a planned PKP. Conditions that may affect the ocular surface include rosacea, dry eyes, blepharitis, trichiasis, exposure keratopathy, ectropion, and entropion.



  • Intraocular pressure (IOP) must be controlled adequately prior to surgery.



  • Ocular inflammation must be recognized and treated.



  • Previous corneal diseases and vascularization must be considered. A history of herpetic keratitis significantly reduces the chance of graft success because of several factors, including recurrent disease in the graft, neovascularization, trabeculitis with increased IOP, and persistent inflammation that may induce rejection.



Donor Selection


The Eye Bank Association of America has developed a set of criteria for donor corneas. Contraindications for the use of donor tissue for PKP include the following:




  • Death as a result of an unknown cause.



  • Central nervous system diseases, such as Creutzfeldt–Jakob disease, subacute sclerosing panencephalitis, rubella, Reye’s syndrome, rabies, meningitis, and infectious encephalitis.



  • Systemic infections, such as human immunodeficiency virus (HIV) infection, hepatitis viruses B and C infection, septicemia, syphilis, Ebola, and infective endocarditis, as well as other relevant communicable diseases, such as West Nile virus, vaccinia virus, or Zika virus infections.



  • Leukemia or actively disseminated lymphomas.



  • History of melanoma with known metastatic disease.



  • Eye diseases, such as retinoblastoma, malignant tumors of the anterior segment, and active ocular inflammation (e.g., uveitis, scleritis, retinitis, and choroiditis).



  • Prior ocular surgery, including refractive procedures. (Eyes with previous laser photoablation surgery may be used for tectonic grafts and posterior lamellar procedures, and pseudo-phakic eyes and eyes that have undergone glaucoma filtration surgery may be used if they meet endothelial criteria by specular microscopy.)



  • Congenital or acquired anterior segment abnormalities, such as corneal scars, keratoconus or Fuchs’ endothelial dystrophy, or associated conditions, such as Down syndrome (for penetrating or anterior lamellar keratoplasty).



Prior to PKP, the donor’s history and blood must be evaluated for communicable diseases, and donor tissues are inspected by the surgeon with the slit lamp.


Surgical Techniques


Adequate decompression of the globe is ensured prior to PKP because excessive preoperative IOP may increase the risk of expulsive choroidal hemorrhage. Intravenous mannitol or mechanical ocular decompression can be considered to reduce IOP. Miotics are placed preoperatively to protect the lens during surgery unless lenticular surgery also is planned. Scleral supporting (Flieringa) rings may be used principally in aphakic eyes or young patients.


The size of the graft is determined on the basis of the location of the pathology and on clinical judgment. The donor tissue usually is 0.25 mm larger in diameter compared with the recipient tissue. In certain circumstances, a larger (0.5 mm) donor may be considered in an aphakic eye to induce myopia, or a same-size donor button, such as in a recipient with keratoconus, may be chosen to reduce myopia. The visual axis of the recipient cornea is marked with a marking pen. An inked radial keratotomy marker may be used to mark the peripheral cornea. A donor corneal button is punched. In the United States, the most commonly used trephine is the Barron Donor Cornea Punch ( Fig. 4.27.1 ). The donor is cut from endothelium to the epithelium. The donor also may be cut from the epithelium to the endothelium by using an artificial anterior chamber and then by using the same technique described for the recipient cornea. This has the theoretical advantage of both the donor and the recipient being cut in the same fashion with the same type of blade, which reduces donor–recipient disparity and potentially reduces astigmatism.




Fig. 4.27.1


The Corneal Donor Button Is Cut.

A Barron donor cornea punch may be used to cut the donor tissue from the endothelial side.


The recipient cornea may be cut using a variety of trephines, such as the Hessburg–Barron suction trephine ( Fig. 4.27.2 ), Hanna trephine, or Castroviejo trephine. More recently, the use of the femtosecond laser to cut the recipient cornea has been described. Excision of the host corneal button may be performed via partial-thickness trephination followed by a controlled entry into the anterior chamber using a No. 75 blade, or via a continued trephination that is stopped as soon as aqueous egress shows the anterior chamber has been entered. If viscoelastic was not placed into the anterior chamber prior to host trephination, it may be placed to protect intraocular structures. The recipient button is then excised using forceps and corneal scissors ( Fig. 4.27.3 ). The edge of the recipient bed is made perpendicular for optimal graft–host apposition.




Fig. 4.27.2


Hessburg–Barron Vacuum Trephine.

A vacuum corneal trephine may be used to trephinate into the host cornea.



Fig. 4.27.3


Excision of the Corneal Button.

The corneal button is removed completely using corneal scissors.


If the patient requires concurrent cataract extraction, intraocular lens (IOL) explantation, iridectomy, anterior vitrectomy, or a secondary IOL, this may be done prior to trephination if visualization allows. Because the diseased cornea precludes adequate visualization in many cases, an “open sky” technique is utilized after trephination ( Fig. 4.27.4 ). In cases of emergent grafting, such as in the setting of an active infectious process, uncontrolled inflammatory disease, or a recent perforation, an iridectomy is performed to avoid pupillary block.




Fig. 4.27.4


Replacement of Anterior Chamber Intraocular Lens.

(A) Care is taken when the anterior chamber haptics are removed, as they may become encysted in the peripheral iris and bleeding may occur on removal. (B) An anterior vitrectomy is performed—an iris hook may be used to improve visualization. (C) A 10-0 Prolene suture is passed beneath the iris, through the scleral sulcus and out through the previously prepared scleral flap. After the suture-supported lens is placed in the sulcus, the suture is tied to itself beneath the scleral flap. Alternatively, the knot may be rotated beneath the sclera. This is performed on both sides.

(Courtesy Dr. W. W. Culbertson.)






Viscoelastic may be placed in the anterior chamber, and the donor button then is placed over the recipient bed and sutured in place with four cardinal sutures ( Fig. 4.27.5 ). Care is taken in the placement of the cardinal sutures, as proper tissue distribution is paramount. The depth of suture is 90% of the corneal thickness. The remaining sutures may be a combination of interrupted and running sutures or solely interrupted sutures ( Fig. 4.27.6 ). Interrupted sutures are suited for vascularized or thinned cornea, as subsequent selective removal may be necessary to prevent the advancement of vessels or to control astigmatism. Running sutures have the advantage of speedy placement intraoperatively and better tension distribution but are more difficult to adjust. Prior to the placement of the final sutures, the viscoelastic material in the anterior chamber is removed. The running sutures may be adjusted intraoperatively by using a keratoscope. When the suturing is complete, all sutures are rotated such that the knots are buried within the stroma, and the security of the wound is tested for water tightness by using a combination of a surgical sponge and fluorescein.




Fig. 4.27.5


The Corneal Button Is Placed.

Care is taken in the placement of cardinal sutures to ensure appropriate distribution.



Fig. 4.27.6


Placement of 10-0 nylon interrupted sutures in a corneal transplant.


Complications and Postoperative Management


Intraoperative complications include poor graft centration, bleeding, damage to ocular structures (e.g., donor endothelium, iris, lens, or lens capsule), or expulsive suprachoroidal hemorrhage. During excision of the recipient button, it is imperative to continuously monitor the depth of the anterior chamber and the red reflex. A sudden shallowing of the anterior chamber or disappearance of the red reflex may signify an impending expulsive choroidal hemorrhage. Sealing of the globe can be accomplished quickly by a gloved finger over a partially excised host cornea or with placement of a donor cornea or temporary keratoprosthesis. The key management strategy is to close and repressurize the globe.


The success of PKP depends significantly on adequate postoperative care and management. The surgeon must be able to recognize and manage a variety of possible complications, such as wound leak, infection, glaucoma, and graft rejection or failure. The common postoperative complications and their management are discussed in the following subsections.


Wound Leak.


A shallow anterior chamber in a soft globe the day after PKP may indicate a wound leak, which may need patching, aqueous suppressant, lubrication, or bandage contact lenses. Resuturing of the wound may be required if the leak is significant.


Flat Anterior Chamber With Increased Intraocular Pressure.


Flat anterior chamber with increased IOP may result from pupillary block, anterior rotation of the lens–iris diaphragm (as found in choroidal hemorrhage), choroidal effusion, or aqueous misdirection. The cause must be identified and treated.


Endophthalmitis.


Postoperative endophthalmitis, a devastating complication, may result from a variety of factors, including contamination of donor tissue, prior infection in the host, or postoperative infection acquired through a wound leak.


Persistent Epithelial Defect.


Epithelial defects that persist beyond 1–2 weeks occur more commonly in eyes that have ocular surface disorders, such as limbal stem cell deficiency, neurotrophic keratopathy, dry eye disease (DED), blepharitis, exposure keratopathy, and rosacea. Treatment includes frequent lubrication with preservative-free drops and lubricating ointment. Possible causes of ocular surface toxicity, such as topical eyedrops, must be eliminated or minimized. If the defect does not heal, ophthalmic blood derivatives, a tarsorrhaphy, or punctal occlusion may be necessary.


Primary Graft Failure.


Primary graft failure (which is different from graft rejection) is recognized when significant edema of the donor tissue in a noninflamed eye is present on the first postoperative day and does not clear by 2–4 weeks. Primary graft failure may be attributed to either poor donor endothelial function or iatrogenic damage to the donor tissue during PKP. The graft is observed for several weeks. Graft failure should be differentiated from Descemet’s membrane detachment. A regraft (either repeat PKP or EKP) is considered if the corneal edema fails to resolve.


Suture-Related Problems.


Loose or broken sutures must be removed to prevent associated infection or neovascularization, which can increase the likelihood of rejection.


Graft Rejection.


Graft rejection remains the most common cause of graft failure. The overall incidence of endothelial graft rejection has been reported as 20%. Symptoms include decreased vision, redness, photophobia, and pain; however, patients may experience as few as one or even none of these symptoms. Patients must be educated carefully about these symptoms and must be instructed to seek medical attention immediately should they occur.


Graft rejection may be divided anatomically into three categories:




  • Epithelial rejection —may be recognized by observation of an epithelial line. This is seen early before the host epithelium replaces the donor epithelium.



  • Subepithelial rejection —multiple subepithelial infiltrates limited to the corneal graft may be observed ( Fig. 4.27.7 ).




    Fig. 4.27.7


    Subepithelial infiltrates secondary to subepithelial graft rejection.

    (Courtesy Dr. W. W. Culbertson.)



  • Endothelial rejection (the most severe type of rejection)—characterized by keratic precipitates, iritis, and corneal edema. A Khodadoust line may be seen, which represents the advancing front of the host’s inflammatory cells against a receding front of donor endothelium ( Fig. 4.27.8 ).




    Fig. 4.27.8


    Graft Rejection.

    Note the inflammatory precipitates and Khodadoust line secondary to endothelial rejection.

    (Courtesy Dr. A. Galor.)



The treatment of graft rejection consists primarily of corticosteroids, usually in topical form. The frequency of the corticosteroid drops is increased to hourly or even more often in the case of endothelial graft rejection until the process is reversed. Subconjunctival or Subtenon’s injection of corticosteroids may be used. Systemic corticosteroids (oral or intravenous) also may be utilized in severe cases. For patients with a history of multiple rejection episodes either in the current cornea or previous grafts, systemic immunomodulatory therapy may be considered.


Treatment for Astigmatism.


Adequate control of postoperative astigmatism is vital to achieving the best-corrected visual acuity possible. Typically starting at 8–12 weeks after PKP, the patient is followed using serial corneal topography. Subsequently, interrupted sutures are removed selectively, and running sutures are adjusted, as necessary to reduce astigmatism. Early suture removal may have a more significant effect on astigmatism, although care is required with regard to wound stability.


Corneal Ulcers.


Patients who have undergone PKP are more susceptible to infectious keratitis. Such factors as loose sutures and persistent epithelial defects may contribute to the development of corneal ulcers.


Recurrence of Diseases.


Various corneal dystrophies and infections may recur in grafts. Among the three most common stromal corneal dystrophies [macular, granular ( Fig. 4.27.9 ), and lattice], lattice corneal dystrophy has the highest recurrence. In the setting of keratic precipitates on a graft in a patient who has a history of herpes simplex virus infection, it is sometimes difficult to distinguish recurrence of a disease from graft rejection. It is important, however, to make such a distinction as the treatment for a recurrence of herpes simplex virus (antiviral agent ± corticosteroid) is different from treatment for rejection (corticosteroid alone). The observation of keratic precipitates and corneal edema confined only to the donor button may suggest graft rejection. Anterior chamber paracentesis and polymerase chain reaction analysis can aid in the diagnosis.




Fig. 4.27.9


Recurrence of Granular Dystrophy in a Graft.

(A) Slit-lamp photograph of a granular dystrophy recurrence in a penetrating keratoplasty graft. (B) Anterior segment optical coherence tomography (AS-OCT) image of recurrence showing location on Bowman’s layer.

(Courtesy Dr. C. Karp.)




Anterior Lamellar Keratoplasty


A concept that has gained popularity in the treatment of corneal disease is the selective removal of only the diseased tissue. Lamellar keratoplasty is a procedure in which a partial-thickness graft of donor tissue is used to provide tectonic stability or optical improvement. A partial-thickness section of donor stroma or sclera may be used. Two types of lamellar keratoplasty exist: anterior lamellar keratoplasty (ALK) and posterior lamellar keratoplasty (also referred to as endothelial keratoplasty ) (see Chapter 4.29 ).


In ALK, the transplanted tissue does not include corneal endothelium, thus avoiding endothelial rejection and allowing donor tissue to be obtained from older eyes. Indications for ALK mainly include anterior corneal pathology in which the posterior cornea is unaffected, such as keratoconus, anterior corneal scars, and corneal dystrophies limited to the stroma. Femtosecond lasers can aid in this procedure. A subtype of ALK is deep anterior lamellar keratoplasty (DALK), in which the objective is to eliminate all of the host stromal tissue; this can be achieved through the use of manual dissection, viscoelastic, or an air bubble, to dissect the host’s stromal–Descemet’s membrane interface.


Preoperative Evaluation and Diagnostic Approach


A tectonic graft is performed to reinforce areas of perforated or thinned cornea. Optical lamellar grafts are used to replace diseased anterior cornea to improve visual function and require that the posterior stroma of the recipient is healthy.


The rationale for a lamellar keratoplasty and the various surgical options must be thoroughly discussed with patients. Different modalities can be used to assess the depth of a scar, the adequacy of the planned remnant stromal bed, and the severity of endothelial disease, including topography, anterior segment optical coherence tomography (AS-OCT), and specular microscopy.


Donor Selection


Donor Preparation.


Criteria for donor tissue selection and screening are the same as those listed for PKP except that tissue with local eye disease affecting the corneal endothelium or previous ocular surgery that does not compromise the corneal stroma (e.g., a history of endothelial dystrophy or iritis) are acceptable.


In ALK, a fresh or frozen whole donor eye or a corneoscleral donor and artificial anterior chamber may be used to fashion the anterior lamellar donor tissue. When done manually, an incision is made just inside the limbus of the donor cornea to reach the depth of the desired dissection. A Martinez dissector or a cyclodialysis spatula is used to extend the dissection plane within the corneal stroma and harvest the donor tissue ( Fig. 4.27.10 ). The tissue harvested may be circular, annular, or any other shape, depending on the needs of the patient ( Fig. 4.27.11 ). Both the cornea and the sclera may be used. Usually, the donor tissue is slightly oversized (0.25–0.5 mm) in width and thickness compared with the recipient bed. Donor tissue suitable for PKP should be available in case of a large perforation that may occur in the lamellar dissection of the host tissue. Newer microkeratomes allow for more efficient host and donor dissection. In particular, the femtosecond laser has been helpful in performing lamellar keratoplasty.




Fig. 4.27.10


Separation of the Cadaveric Cornea.

A dissector, such as the Martinez dissector or a cyclodialysis spatula, is used to gently separate the cornea along the lamellar cleavage plane through the entire cornea.



Fig. 4.27.11


Donor Tissue Is Harvested.

A trephine is placed on the cadaveric globe in the size and shape desired. A horseshoe or annular lamellar graft is being harvested here. A combination of corneal and scleral tissue may be harvested to give a different tissue shape.


Surgical Techniques


Anterior Lamellar Dissection of the Host Tissue.


A measurement of the affected area is done, and this can be facilitated by OCT preoperatively. A trephine is used gently to mark the extent of graft needed. The surgeon may opt for a manual dissection of the host stroma or air-assisted dissection using the “big bubble” technique, as described by Anwar. Irrespective of the technique chosen, the goal is to create a smooth, uniplanar recipient bed. Elimination of most or all of the host stroma will lead to better final visual outcomes by eliminating stroma-to-stroma interface. If Descemet’s membrane is violated, the procedure is then converted to a PKP, although conversion may be avoided in the setting of small perforations.


If a manual dissection is chosen, a partial-thickness trephination is performed until the desired depth of dissection is reached ( Fig. 4.27.12 ). Alternatively, a microkeratome or femtosecond laser may be used for the host. A blade is then used to extend the dissection plane along the entire host corneal tissue until the dissection of the host tissue is completed ( Fig. 4.27.13 ). In manual ALK, the edge of the host bed should be undermined to create a horizontal groove using a Paufique knife. The donor lamella is placed on the recipient bed and secured with interrupted 10-0 nylon sutures ( Fig. 4.27.14 ). The depth of the suture is about 90% of the corneal stromal depth. The donor tissue margins should not ride anteriorly to the rim of the recipient bed. At times, an anterior chamber paracentesis may become necessary before lamellar sutures are placed. ALK may be performed centrally or in the periphery for corneoscleral melts ( Figs. 4.27.15 and 4.27.16 ).




Fig. 4.27.12


Partial-Thickness Trephination.

This is performed on the host in the desired location and to the desired depth. Care must be taken not to perforate the cornea.



Fig. 4.27.13


Dissection of the Diseased Area.

The diseased area in the host cornea is dissected gently to create a uniplanar, disease-free bed.



Fig. 4.27.14


The Lamellar Tissue Is Sutured to the Host Bed.

Suture placement is facilitated if the edge of the host bed is undermined. Traditionally, the graft is sutured with 10-0 nylon.



Fig. 4.27.15


Lamellar Keratoplasty for Granular Dystrophy.

(A) Preoperative appearance of a patient who had granular dystrophy limited to the anterior cornea. (B) Postoperative appearance following manual lamellar keratoplasty.

(Courtesy Dr W. W. Culbertson.)





Fig. 4.27.16


Lamellar Keratoplasty for Peripheral Corneal Melt and Perforation.

(A) Preoperative appearance of a patient who had a peripheral corneal melt and perforation (see arrows). (B) Postoperative appearance after the placement of a horseshoe corneoscleral lamellar graft.

(Courtesy Dr. W. W. Culbertson.)




In DALK, a deep anterior lamellar disc is trephined to about 80% total depth, or the femtosecond laser can be used for this part of the procedure. A paracentesis can be done at this point to inject a small air bubble in the eye to improve visualization of the big bubble because it will push it to the periphery of the anterior chamber; a mild decrease in anterior chamber pressure will also decrease resistance to the big bubble. Some surgeons advocate debulking of the anterior half of the stroma before proceeding with air dissection, whereas others proceed directly with a 27-gauge needle or cannula (previously having created a track with a dissector) to the center of the cornea ( Fig. 4.27.17 ). Using a 5-cc syringe, air is applied firmly to create a bubble. Two types of bubbles have been described. A type 1 bubble occurs when the stroma is dissected at the level of pre-Descemet’s layer; this yields a smaller bubble with greater structural integrity (higher bursting pressure). A type 2 bubble occurs when the cleavage happens between Descemet’s and pre-Descemet’s layers, producing a larger bubble with a thinner wall and a lower bursting pressure.




Fig. 4.27.17


Deep Anterior Lamellar Keratoplasty (DALK).

(A) After 80% trephination the 30-gauge needle is advanced until it reaches the center of the cornea. (B) Air is released firmly and steadily forming a big bubble, in this case a type 1 bubble was formed. (C) A “brave slash” is performed to access the bubble. (D) Dissection of the anterior lamella is performed until Descemet’s membrane is exposed. (E) The endothelium is removed from the donor cornea, then the donor cap is sutured to the host. (F) Final result.

(Courtesy Dr. F. A. Valenzuela.)












Viscoelastic material may then be injected into the space created by the air bubble to facilitate further separation of the layers. The deep stromal layers are excised, usually in quadrants (see Fig. 4.27.17 ). The intraoperative OCT can aid in determining dissection depth. All viscoelastic material is removed to avoid a dual anterior chamber. A donor button, the same size as the trephination, is then placed after the removal of Descemet’s membrane and the endothelium and secured using 10-0 nylon sutures.


In femtosecond-assisted lamellar keratoplasty (FALK), the donor and recipient are cut with the femtosecond laser, and the donor lenticule can be placed without sutures on the recipient bed ( Fig. 4.27.18 ). Only a bandage contact lens is used in cases when the residual stromal bed is thicker than 250 microns.




Fig. 4.27.18


Femtosecond-Assisted Lamellar Keratoplasty (FALK).

(A) Residual granular dystrophy and central corneal scar seen in a patient after corneal transplantation. When the dystrophy recurred, phototherapeutic keratectomy (PTK) had been performed on the PTK, which eliminated some of the granular deposits but caused some corneal haze. (B) After FALK—FALK was performed to remove the corneal haze and residual anterior granular deposits. FALK (arrowheads) was centered over the visual axis, not over the corneal graft (arrows).

(Courtesy Dr. C. L. Karp.)




Complications and Postoperative Management


In general, anterior lamellar grafts can be very successful (see Figs. 4.27.15 and 4.27.16 ). Complications of ALK are less frequent or less severe in nature compared with those of PKP. Complications of lamellar graft include perforation of the recipient cornea, interface scarring and vascularization, persistent epithelial defect, inflammatory necrosis of the graft and graft melting, infection, astigmatism, and allograft rejection. Careful irrigation and cleaning of the host bed may reduce the incidence of complications. ALK has a significantly reduced incidence of allograft rejection because no transplantation of foreign endothelium is involved.


Perforation of Descemet’s Membrane.


This is a relatively common event early in the surgical learning curve. In small perforations, the case can proceed as planned, but the surgeon should leave a gas bubble (air or SF6 20%) in the eye to ensure that Descemet’s membrane remains attached to the stroma. In larger perforations, a combination of gas and a pass-through suture may be necessary to anchor Descemet’s membrane and avoid its retraction. In larger breaks, conversion to PKP may be required.


Pseudo-Anterior Chamber.


A double anterior chamber may occur when an unrecognized Descemet’s tear occurs, such as during suturing of the donor graft. Moreover, viscoelastic material has been implicated in certain cases. The dual chamber may resolve spontaneously, but most surgeons inject air or SF6 20% in the early postoperative period to enhance recovery times and potential endothelial cell loss.


Triple Procedure (Combined Procedure)


A triple procedure or combined procedure refers to keratoplasty, combined with cataract extraction and IOL implantation.


Preoperative Evaluation and Diagnostic Approach


The triple procedure is indicated for patients with a visually significant cataract who also require corneal transplantation for visual rehabilitation. Triple procedures are increasingly being performed with the use of the DSAEK or DMEK technique for patients with endothelial disease. If visualization permits, cataract extraction may be performed in a closed system by using standard phacoemulsification techniques. The leading indication for a triple procedure is Fuchs’ endothelial dystrophy and cataract, which accounts for up to 77% of eyes that require a triple procedure.


Compared with PKP, a combined procedure requires the additional calculation of the power of the IOL. Different formulas, such as the Holladay or the Sanders–Retzlaff–Kraff formula ( Eq. 4.27.1 ), in which A is the constant for an IOL, AL is the axial length, and K is the keratometric measurement. The determination of K varies from surgeon to surgeon. The authors typically advocate one of two alternative approaches, using either the average of the surgeon’s past postoperative keratometric readings associated with the surgical technique or the K readings from the contralateral eye. In the instances in which an over- or undersized graft is required, +1.00–+2.00 diopters (D) is subtracted from the IOL power for a 0.5-mm oversized graft or +1.00–+2.00 D is added to the IOL power for 0.5-mm undersizing. Postoperative refractive targets must be adjusted in DSAEK or DMEK triple procedures, as there may be a hyperopic shift associated with these procedures.


<SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='IOL power=A−2.5AL−0.9K’>IOL power=𝐴2.5𝐴𝐿0.9𝐾IOL power=A−2.5AL−0.9K
IOL power=A−2.5AL−0.9K


Surgical Techniques


Open Sky Cataract Extraction.


The detailed surgical technique for PKP is described above. Prior to the trephination of the recipient cornea, trypan blue may be considered for visual augmentation of the capsulotomy. After the recipient button has been excised, a capsulorrhexis, sufficiently large to allow subsequent expression of the lens nucleus, is performed. Caution is maintained during the capsulorrhexis because there is a tendency for the capsulectomy to extend peripherally, especially with increased posterior pressure.


After hydrodissection and mobilization of the lens nucleus, the lens is gently expressed. The remaining cortical material is removed carefully using an automated irrigation–aspiration instrument or a manual I/A, as the anterior and posterior capsules tend to collapse toward each other. The capsular bag is then inflated with viscoelastic material, and the appropriate posterior chamber IOL is inserted. The authors of this chapter prefer a rigid or a three-piece IOL in this scenario for increased stability because of anterior chamber fluctuations. If a posterior capsular tear and anterior prolapse of vitreous occur, a limited anterior vitrectomy is performed, and the IOL is inserted either into the ciliary sulcus and sutured to the iris or sclera or an open-loop anterior chamber IOL may be used. The remainder of the procedure for PKP is the same as described previously.


Artificial Cornea (Keratoprosthesis)


Keratoprosthesis implantation is performed in patients in whom corneal transplantation is considered high risk, with a very high likelihood of graft failure, such as those with a history of multiple graft failures or deep neovascularization of the cornea.


Boston K-Pro


The Boston Keratoprosthesis (K-Pro) (formerly known as the Dohlman–Doane Kpro ) has been under development since the 1960s. It received Food and Drug Administration (FDA) approval for commercialization in 1992. It is the most commonly used keratoprosthesis in the world. The keratoprosthesis is made of clear polymethyl methacrylate (PMMA) plastic and has two pieces that take the shape of a collar button. The device is inserted into a corneal graft, which is then transplanted into the recipient’s cloudy cornea. There are two types of the Boston K-Pro: (1) type I, available in phakic and pseudo-phakic versions, is used in patients with an adequate ocular surface, and (2) type II, which is placed through the lids in patients with severe ocular surface disease.


AlphaCor


The AlphaCor implant, approved by the FDA in 2003, is made of a flexible hydrogel material similar to a soft contact lens. It contains a central clear zone that provides refractive power and a peripheral skirt or rim made of a special material that encourages the eye to heal over the device. The device is available in two powers: one for aphakic and one for phakic patients. The two-stage surgery involves the initial implantation of the AlphaCor device into the cornea of the recipient and the creation of a protective conjunctival flap over the prosthesis. The subsequent removal of the flap allows light to pass through the central clear zone to restore vision.


A retroprosthetic membrane can occur following implantation of any artificial cornea and can be removed by using a YAG (neodymium-doped yttrium aluminum garnet) laser, unless highly vascular. Migration of the AlphaCor under the lamellar flap can occur.


Modified Osteo-Odonto-Keratoprosthesis


The osteo-odonto-keratoprosthesis (OOKP) was first described in Italy and documented in 1963 by Benedetto Strampelli and later modified by Giancarlo Falcinelli et al. for the treatment of bilateral corneal blindness in patients with end-stage ocular surface disorders. Falcinelli’s group has completed more than 220 cases, with an anatomical success rate of 94% and a mean follow-up of 9.4 years. The first modified OOKP (MOOKP) was performed in the United States in 2009.


The newer MOOKP consists of a cylindrical PMMA lens embedded within the patient’s own tissue (heterotopic autograft of the patient’s tooth root and alveolar bone). The complete implantation is a three-stage procedure. Initially, the lens, iris, and vitreous are removed from the eye. A portion of the tooth (preferably canine), bone, and periodontal complex is concurrently resected, typically with the assistance of an oral maxillofacial surgeon, and shaped into a thin rectangular lamina. Some surgeons advocate the procurement of the bone lamina from the tibia. The PMMA lens is mounted into the center of the lamina, and the complex is placed into a subcutaneous pocket. After 1–2 months, a patch of buccal mucosa is obtained and sutured over the scarred and vascularized ocular surface. Alternatively, the first two stages may be performed simultaneously. After a minimum period of 3 months, the lamina is retrieved from the subcutaneous pocket. After trephinating appropriately into both the cornea and oral mucosa for the cylindrical lens, the prosthesis is then secured to the surface of the eye between the layers of the scarred cornea and buccal mucosa using absorbable suture ( Fig. 4.27.19 ).




Fig. 4.27.19


Modified Osteo-Odonto Keratoprosthesis (MOOKP).

Schematic drawing of the placement of the osteo-odonto-keratoprosthesis between the grafted buccal mucosa and the scarred and vascularized ocular surface.

(Courtesy Sawatari S, Perez VL, Parel JM, et al. Oral and maxillofacial surgeons’ role in the first successful modified osteo-odonto-keratoprosthesis performed in the United States. J Oral Maxillofac Surg 2011:69:1750–56, by kind permission.)


Like any other type of keratoprosthesis, patients after MOOKP require lifelong follow-up. Early in the postoperative period, a need exists for topical broad spectrum antibiotics. Once the mucosa is healed, there is no need for chronic topical antibiotic treatment. Multiple complications can occur after MOOKP, including glaucoma, which is the most common cause for loss of vision after MOOKP. For this reason, patients need IOP estimation (by finger palpation of the globe) and optic nerve head evaluation at every visit.


Outcome


Corneal grafting techniques, such as PKP, ALK, and triple procedures, have become reliable and popular surgical techniques. Careful attention to preoperative evaluation, surgical techniques, and postoperative management will improve surgical outcome and patients’ satisfaction.




Introduction


The successful outcomes enjoyed by patients who undergo modern penetrating keratoplasty (PKP) and lamellar keratoplasty are the result of advances in technology and surgical techniques.




Historical Review


Corneal grafting techniques were pioneered by ophthalmologists, such as Reisinger, von Hippel, and Elschnig. Today keratoplasty is the most common and successful human transplantation procedure, with over 45 000 corneal transplantations performed in the United States each year. The number of PKP decreased to less than 20 000 in the year 2014, and the number of endothelial keratoplasty (EKP) increased to over 25 000 in that same year. Optical results have improved significantly as a consequence of advances in tissue selection and preservation, techniques, trephines, and management of postoperative astigmatism.


Lamellar grafts date back to 1886 when von Hippel successfully performed the first lamellar grafting in a human. Lamellar techniques have revolutionized the treatment of corneal diseases by offering such advantages as faster visual recovery, less postoperative astigmatism, and decreased risk of suture-related complications compared with PKP. Because “selective keratoplasty” replaces only the diseased tissue, the risk of graft rejection is theoretically lower. EKP now has become the standard of care for endothelial diseases.




Anesthesia


Corneal transplantation may be performed under cover of regional or general anesthesia, depending on patient preference and cooperation. Typically, local anesthesia entails peribulbar or retrobulbar injection of lidocaine 2%, bupivacaine 0.75%, and hyaluronidase. A lid block may be employed to prevent squeezing.




Specific Techniques


Penetrating Keratoplasty


PKP involves full-thickness replacement of corneal tissue with a healthy donor graft.


Preoperative Evaluation and Diagnostic Approach


PKP may be used to provide tectonic support (as in corneal thinning or perforation) and to improve visual outcomes (as in the replacement of an opaque or irregular cornea). Indications for PKP include keratoconus; previous graft failure or rejection; full-thickness or deep corneal scars; Fuchs’ endothelial dystrophy; pseudo-phakic or aphakic bullous keratopathy; chemical burn; corneal ulcer; corneal dystrophy and degeneration; herpetic keratitis; trauma; or any other causes of corneal decompensation. Conditions with primarily posterior pathologies, such as Fuchs’ endothelial dystrophy and pseudo-phakic or aphakic bullous keratopathy, now are commonly treated with EKP. The rate of success of PKP is excellent, but the long-term risk of graft rejection increases significantly with active or recurrent infection, inflammation, corneal neovascularization, previous graft rejection, and each subsequent penetrating graft.


It is important to perform a careful preoperative evaluation and have a thorough discussion with patients about the surgery, visual expectation, possible complications, and the long postoperative course. The recipient must be prepared for the lifelong care required. In general, important considerations for the preoperative evaluation for PKP are as follows:




  • Visual potential must be evaluated.



  • Ocular surface must be optimized before a planned PKP. Conditions that may affect the ocular surface include rosacea, dry eyes, blepharitis, trichiasis, exposure keratopathy, ectropion, and entropion.



  • Intraocular pressure (IOP) must be controlled adequately prior to surgery.



  • Ocular inflammation must be recognized and treated.



  • Previous corneal diseases and vascularization must be considered. A history of herpetic keratitis significantly reduces the chance of graft success because of several factors, including recurrent disease in the graft, neovascularization, trabeculitis with increased IOP, and persistent inflammation that may induce rejection.



Donor Selection


The Eye Bank Association of America has developed a set of criteria for donor corneas. Contraindications for the use of donor tissue for PKP include the following:




  • Death as a result of an unknown cause.



  • Central nervous system diseases, such as Creutzfeldt–Jakob disease, subacute sclerosing panencephalitis, rubella, Reye’s syndrome, rabies, meningitis, and infectious encephalitis.



  • Systemic infections, such as human immunodeficiency virus (HIV) infection, hepatitis viruses B and C infection, septicemia, syphilis, Ebola, and infective endocarditis, as well as other relevant communicable diseases, such as West Nile virus, vaccinia virus, or Zika virus infections.



  • Leukemia or actively disseminated lymphomas.



  • History of melanoma with known metastatic disease.



  • Eye diseases, such as retinoblastoma, malignant tumors of the anterior segment, and active ocular inflammation (e.g., uveitis, scleritis, retinitis, and choroiditis).



  • Prior ocular surgery, including refractive procedures. (Eyes with previous laser photoablation surgery may be used for tectonic grafts and posterior lamellar procedures, and pseudo-phakic eyes and eyes that have undergone glaucoma filtration surgery may be used if they meet endothelial criteria by specular microscopy.)



  • Congenital or acquired anterior segment abnormalities, such as corneal scars, keratoconus or Fuchs’ endothelial dystrophy, or associated conditions, such as Down syndrome (for penetrating or anterior lamellar keratoplasty).



Prior to PKP, the donor’s history and blood must be evaluated for communicable diseases, and donor tissues are inspected by the surgeon with the slit lamp.


Surgical Techniques


Adequate decompression of the globe is ensured prior to PKP because excessive preoperative IOP may increase the risk of expulsive choroidal hemorrhage. Intravenous mannitol or mechanical ocular decompression can be considered to reduce IOP. Miotics are placed preoperatively to protect the lens during surgery unless lenticular surgery also is planned. Scleral supporting (Flieringa) rings may be used principally in aphakic eyes or young patients.


The size of the graft is determined on the basis of the location of the pathology and on clinical judgment. The donor tissue usually is 0.25 mm larger in diameter compared with the recipient tissue. In certain circumstances, a larger (0.5 mm) donor may be considered in an aphakic eye to induce myopia, or a same-size donor button, such as in a recipient with keratoconus, may be chosen to reduce myopia. The visual axis of the recipient cornea is marked with a marking pen. An inked radial keratotomy marker may be used to mark the peripheral cornea. A donor corneal button is punched. In the United States, the most commonly used trephine is the Barron Donor Cornea Punch ( Fig. 4.27.1 ). The donor is cut from endothelium to the epithelium. The donor also may be cut from the epithelium to the endothelium by using an artificial anterior chamber and then by using the same technique described for the recipient cornea. This has the theoretical advantage of both the donor and the recipient being cut in the same fashion with the same type of blade, which reduces donor–recipient disparity and potentially reduces astigmatism.




Fig. 4.27.1


The Corneal Donor Button Is Cut.

A Barron donor cornea punch may be used to cut the donor tissue from the endothelial side.


The recipient cornea may be cut using a variety of trephines, such as the Hessburg–Barron suction trephine ( Fig. 4.27.2 ), Hanna trephine, or Castroviejo trephine. More recently, the use of the femtosecond laser to cut the recipient cornea has been described. Excision of the host corneal button may be performed via partial-thickness trephination followed by a controlled entry into the anterior chamber using a No. 75 blade, or via a continued trephination that is stopped as soon as aqueous egress shows the anterior chamber has been entered. If viscoelastic was not placed into the anterior chamber prior to host trephination, it may be placed to protect intraocular structures. The recipient button is then excised using forceps and corneal scissors ( Fig. 4.27.3 ). The edge of the recipient bed is made perpendicular for optimal graft–host apposition.




Fig. 4.27.2


Hessburg–Barron Vacuum Trephine.

A vacuum corneal trephine may be used to trephinate into the host cornea.



Fig. 4.27.3


Excision of the Corneal Button.

The corneal button is removed completely using corneal scissors.


If the patient requires concurrent cataract extraction, intraocular lens (IOL) explantation, iridectomy, anterior vitrectomy, or a secondary IOL, this may be done prior to trephination if visualization allows. Because the diseased cornea precludes adequate visualization in many cases, an “open sky” technique is utilized after trephination ( Fig. 4.27.4 ). In cases of emergent grafting, such as in the setting of an active infectious process, uncontrolled inflammatory disease, or a recent perforation, an iridectomy is performed to avoid pupillary block.




Fig. 4.27.4


Replacement of Anterior Chamber Intraocular Lens.

(A) Care is taken when the anterior chamber haptics are removed, as they may become encysted in the peripheral iris and bleeding may occur on removal. (B) An anterior vitrectomy is performed—an iris hook may be used to improve visualization. (C) A 10-0 Prolene suture is passed beneath the iris, through the scleral sulcus and out through the previously prepared scleral flap. After the suture-supported lens is placed in the sulcus, the suture is tied to itself beneath the scleral flap. Alternatively, the knot may be rotated beneath the sclera. This is performed on both sides.

(Courtesy Dr. W. W. Culbertson.)






Viscoelastic may be placed in the anterior chamber, and the donor button then is placed over the recipient bed and sutured in place with four cardinal sutures ( Fig. 4.27.5 ). Care is taken in the placement of the cardinal sutures, as proper tissue distribution is paramount. The depth of suture is 90% of the corneal thickness. The remaining sutures may be a combination of interrupted and running sutures or solely interrupted sutures ( Fig. 4.27.6 ). Interrupted sutures are suited for vascularized or thinned cornea, as subsequent selective removal may be necessary to prevent the advancement of vessels or to control astigmatism. Running sutures have the advantage of speedy placement intraoperatively and better tension distribution but are more difficult to adjust. Prior to the placement of the final sutures, the viscoelastic material in the anterior chamber is removed. The running sutures may be adjusted intraoperatively by using a keratoscope. When the suturing is complete, all sutures are rotated such that the knots are buried within the stroma, and the security of the wound is tested for water tightness by using a combination of a surgical sponge and fluorescein.




Fig. 4.27.5


The Corneal Button Is Placed.

Care is taken in the placement of cardinal sutures to ensure appropriate distribution.



Fig. 4.27.6


Placement of 10-0 nylon interrupted sutures in a corneal transplant.


Complications and Postoperative Management


Intraoperative complications include poor graft centration, bleeding, damage to ocular structures (e.g., donor endothelium, iris, lens, or lens capsule), or expulsive suprachoroidal hemorrhage. During excision of the recipient button, it is imperative to continuously monitor the depth of the anterior chamber and the red reflex. A sudden shallowing of the anterior chamber or disappearance of the red reflex may signify an impending expulsive choroidal hemorrhage. Sealing of the globe can be accomplished quickly by a gloved finger over a partially excised host cornea or with placement of a donor cornea or temporary keratoprosthesis. The key management strategy is to close and repressurize the globe.


The success of PKP depends significantly on adequate postoperative care and management. The surgeon must be able to recognize and manage a variety of possible complications, such as wound leak, infection, glaucoma, and graft rejection or failure. The common postoperative complications and their management are discussed in the following subsections.


Wound Leak.


A shallow anterior chamber in a soft globe the day after PKP may indicate a wound leak, which may need patching, aqueous suppressant, lubrication, or bandage contact lenses. Resuturing of the wound may be required if the leak is significant.


Flat Anterior Chamber With Increased Intraocular Pressure.


Flat anterior chamber with increased IOP may result from pupillary block, anterior rotation of the lens–iris diaphragm (as found in choroidal hemorrhage), choroidal effusion, or aqueous misdirection. The cause must be identified and treated.


Endophthalmitis.


Postoperative endophthalmitis, a devastating complication, may result from a variety of factors, including contamination of donor tissue, prior infection in the host, or postoperative infection acquired through a wound leak.


Persistent Epithelial Defect.


Epithelial defects that persist beyond 1–2 weeks occur more commonly in eyes that have ocular surface disorders, such as limbal stem cell deficiency, neurotrophic keratopathy, dry eye disease (DED), blepharitis, exposure keratopathy, and rosacea. Treatment includes frequent lubrication with preservative-free drops and lubricating ointment. Possible causes of ocular surface toxicity, such as topical eyedrops, must be eliminated or minimized. If the defect does not heal, ophthalmic blood derivatives, a tarsorrhaphy, or punctal occlusion may be necessary.


Primary Graft Failure.


Primary graft failure (which is different from graft rejection) is recognized when significant edema of the donor tissue in a noninflamed eye is present on the first postoperative day and does not clear by 2–4 weeks. Primary graft failure may be attributed to either poor donor endothelial function or iatrogenic damage to the donor tissue during PKP. The graft is observed for several weeks. Graft failure should be differentiated from Descemet’s membrane detachment. A regraft (either repeat PKP or EKP) is considered if the corneal edema fails to resolve.


Suture-Related Problems.


Loose or broken sutures must be removed to prevent associated infection or neovascularization, which can increase the likelihood of rejection.


Graft Rejection.


Graft rejection remains the most common cause of graft failure. The overall incidence of endothelial graft rejection has been reported as 20%. Symptoms include decreased vision, redness, photophobia, and pain; however, patients may experience as few as one or even none of these symptoms. Patients must be educated carefully about these symptoms and must be instructed to seek medical attention immediately should they occur.


Graft rejection may be divided anatomically into three categories:




  • Epithelial rejection —may be recognized by observation of an epithelial line. This is seen early before the host epithelium replaces the donor epithelium.



  • Subepithelial rejection —multiple subepithelial infiltrates limited to the corneal graft may be observed ( Fig. 4.27.7 ).




    Fig. 4.27.7


    Subepithelial infiltrates secondary to subepithelial graft rejection.

    (Courtesy Dr. W. W. Culbertson.)



  • Endothelial rejection (the most severe type of rejection)—characterized by keratic precipitates, iritis, and corneal edema. A Khodadoust line may be seen, which represents the advancing front of the host’s inflammatory cells against a receding front of donor endothelium ( Fig. 4.27.8 ).




    Fig. 4.27.8


    Graft Rejection.

    Note the inflammatory precipitates and Khodadoust line secondary to endothelial rejection.

    (Courtesy Dr. A. Galor.)



The treatment of graft rejection consists primarily of corticosteroids, usually in topical form. The frequency of the corticosteroid drops is increased to hourly or even more often in the case of endothelial graft rejection until the process is reversed. Subconjunctival or Subtenon’s injection of corticosteroids may be used. Systemic corticosteroids (oral or intravenous) also may be utilized in severe cases. For patients with a history of multiple rejection episodes either in the current cornea or previous grafts, systemic immunomodulatory therapy may be considered.


Treatment for Astigmatism.


Adequate control of postoperative astigmatism is vital to achieving the best-corrected visual acuity possible. Typically starting at 8–12 weeks after PKP, the patient is followed using serial corneal topography. Subsequently, interrupted sutures are removed selectively, and running sutures are adjusted, as necessary to reduce astigmatism. Early suture removal may have a more significant effect on astigmatism, although care is required with regard to wound stability.


Corneal Ulcers.


Patients who have undergone PKP are more susceptible to infectious keratitis. Such factors as loose sutures and persistent epithelial defects may contribute to the development of corneal ulcers.


Recurrence of Diseases.


Various corneal dystrophies and infections may recur in grafts. Among the three most common stromal corneal dystrophies [macular, granular ( Fig. 4.27.9 ), and lattice], lattice corneal dystrophy has the highest recurrence. In the setting of keratic precipitates on a graft in a patient who has a history of herpes simplex virus infection, it is sometimes difficult to distinguish recurrence of a disease from graft rejection. It is important, however, to make such a distinction as the treatment for a recurrence of herpes simplex virus (antiviral agent ± corticosteroid) is different from treatment for rejection (corticosteroid alone). The observation of keratic precipitates and corneal edema confined only to the donor button may suggest graft rejection. Anterior chamber paracentesis and polymerase chain reaction analysis can aid in the diagnosis.




Fig. 4.27.9


Recurrence of Granular Dystrophy in a Graft.

(A) Slit-lamp photograph of a granular dystrophy recurrence in a penetrating keratoplasty graft. (B) Anterior segment optical coherence tomography (AS-OCT) image of recurrence showing location on Bowman’s layer.

(Courtesy Dr. C. Karp.)




Anterior Lamellar Keratoplasty


A concept that has gained popularity in the treatment of corneal disease is the selective removal of only the diseased tissue. Lamellar keratoplasty is a procedure in which a partial-thickness graft of donor tissue is used to provide tectonic stability or optical improvement. A partial-thickness section of donor stroma or sclera may be used. Two types of lamellar keratoplasty exist: anterior lamellar keratoplasty (ALK) and posterior lamellar keratoplasty (also referred to as endothelial keratoplasty ) (see Chapter 4.29 ).


In ALK, the transplanted tissue does not include corneal endothelium, thus avoiding endothelial rejection and allowing donor tissue to be obtained from older eyes. Indications for ALK mainly include anterior corneal pathology in which the posterior cornea is unaffected, such as keratoconus, anterior corneal scars, and corneal dystrophies limited to the stroma. Femtosecond lasers can aid in this procedure. A subtype of ALK is deep anterior lamellar keratoplasty (DALK), in which the objective is to eliminate all of the host stromal tissue; this can be achieved through the use of manual dissection, viscoelastic, or an air bubble, to dissect the host’s stromal–Descemet’s membrane interface.


Preoperative Evaluation and Diagnostic Approach


A tectonic graft is performed to reinforce areas of perforated or thinned cornea. Optical lamellar grafts are used to replace diseased anterior cornea to improve visual function and require that the posterior stroma of the recipient is healthy.


The rationale for a lamellar keratoplasty and the various surgical options must be thoroughly discussed with patients. Different modalities can be used to assess the depth of a scar, the adequacy of the planned remnant stromal bed, and the severity of endothelial disease, including topography, anterior segment optical coherence tomography (AS-OCT), and specular microscopy.


Donor Selection


Donor Preparation.


Criteria for donor tissue selection and screening are the same as those listed for PKP except that tissue with local eye disease affecting the corneal endothelium or previous ocular surgery that does not compromise the corneal stroma (e.g., a history of endothelial dystrophy or iritis) are acceptable.


In ALK, a fresh or frozen whole donor eye or a corneoscleral donor and artificial anterior chamber may be used to fashion the anterior lamellar donor tissue. When done manually, an incision is made just inside the limbus of the donor cornea to reach the depth of the desired dissection. A Martinez dissector or a cyclodialysis spatula is used to extend the dissection plane within the corneal stroma and harvest the donor tissue ( Fig. 4.27.10 ). The tissue harvested may be circular, annular, or any other shape, depending on the needs of the patient ( Fig. 4.27.11 ). Both the cornea and the sclera may be used. Usually, the donor tissue is slightly oversized (0.25–0.5 mm) in width and thickness compared with the recipient bed. Donor tissue suitable for PKP should be available in case of a large perforation that may occur in the lamellar dissection of the host tissue. Newer microkeratomes allow for more efficient host and donor dissection. In particular, the femtosecond laser has been helpful in performing lamellar keratoplasty.




Fig. 4.27.10


Separation of the Cadaveric Cornea.

A dissector, such as the Martinez dissector or a cyclodialysis spatula, is used to gently separate the cornea along the lamellar cleavage plane through the entire cornea.



Fig. 4.27.11


Donor Tissue Is Harvested.

A trephine is placed on the cadaveric globe in the size and shape desired. A horseshoe or annular lamellar graft is being harvested here. A combination of corneal and scleral tissue may be harvested to give a different tissue shape.


Surgical Techniques


Anterior Lamellar Dissection of the Host Tissue.


A measurement of the affected area is done, and this can be facilitated by OCT preoperatively. A trephine is used gently to mark the extent of graft needed. The surgeon may opt for a manual dissection of the host stroma or air-assisted dissection using the “big bubble” technique, as described by Anwar. Irrespective of the technique chosen, the goal is to create a smooth, uniplanar recipient bed. Elimination of most or all of the host stroma will lead to better final visual outcomes by eliminating stroma-to-stroma interface. If Descemet’s membrane is violated, the procedure is then converted to a PKP, although conversion may be avoided in the setting of small perforations.


If a manual dissection is chosen, a partial-thickness trephination is performed until the desired depth of dissection is reached ( Fig. 4.27.12 ). Alternatively, a microkeratome or femtosecond laser may be used for the host. A blade is then used to extend the dissection plane along the entire host corneal tissue until the dissection of the host tissue is completed ( Fig. 4.27.13 ). In manual ALK, the edge of the host bed should be undermined to create a horizontal groove using a Paufique knife. The donor lamella is placed on the recipient bed and secured with interrupted 10-0 nylon sutures ( Fig. 4.27.14 ). The depth of the suture is about 90% of the corneal stromal depth. The donor tissue margins should not ride anteriorly to the rim of the recipient bed. At times, an anterior chamber paracentesis may become necessary before lamellar sutures are placed. ALK may be performed centrally or in the periphery for corneoscleral melts ( Figs. 4.27.15 and 4.27.16 ).




Fig. 4.27.12


Partial-Thickness Trephination.

This is performed on the host in the desired location and to the desired depth. Care must be taken not to perforate the cornea.



Fig. 4.27.13


Dissection of the Diseased Area.

The diseased area in the host cornea is dissected gently to create a uniplanar, disease-free bed.



Fig. 4.27.14


The Lamellar Tissue Is Sutured to the Host Bed.

Suture placement is facilitated if the edge of the host bed is undermined. Traditionally, the graft is sutured with 10-0 nylon.



Fig. 4.27.15


Lamellar Keratoplasty for Granular Dystrophy.

(A) Preoperative appearance of a patient who had granular dystrophy limited to the anterior cornea. (B) Postoperative appearance following manual lamellar keratoplasty.

(Courtesy Dr W. W. Culbertson.)





Fig. 4.27.16


Lamellar Keratoplasty for Peripheral Corneal Melt and Perforation.

(A) Preoperative appearance of a patient who had a peripheral corneal melt and perforation (see arrows). (B) Postoperative appearance after the placement of a horseshoe corneoscleral lamellar graft.

(Courtesy Dr. W. W. Culbertson.)




In DALK, a deep anterior lamellar disc is trephined to about 80% total depth, or the femtosecond laser can be used for this part of the procedure. A paracentesis can be done at this point to inject a small air bubble in the eye to improve visualization of the big bubble because it will push it to the periphery of the anterior chamber; a mild decrease in anterior chamber pressure will also decrease resistance to the big bubble. Some surgeons advocate debulking of the anterior half of the stroma before proceeding with air dissection, whereas others proceed directly with a 27-gauge needle or cannula (previously having created a track with a dissector) to the center of the cornea ( Fig. 4.27.17 ). Using a 5-cc syringe, air is applied firmly to create a bubble. Two types of bubbles have been described. A type 1 bubble occurs when the stroma is dissected at the level of pre-Descemet’s layer; this yields a smaller bubble with greater structural integrity (higher bursting pressure). A type 2 bubble occurs when the cleavage happens between Descemet’s and pre-Descemet’s layers, producing a larger bubble with a thinner wall and a lower bursting pressure.




Fig. 4.27.17


Deep Anterior Lamellar Keratoplasty (DALK).

(A) After 80% trephination the 30-gauge needle is advanced until it reaches the center of the cornea. (B) Air is released firmly and steadily forming a big bubble, in this case a type 1 bubble was formed. (C) A “brave slash” is performed to access the bubble. (D) Dissection of the anterior lamella is performed until Descemet’s membrane is exposed. (E) The endothelium is removed from the donor cornea, then the donor cap is sutured to the host. (F) Final result.

(Courtesy Dr. F. A. Valenzuela.)












Viscoelastic material may then be injected into the space created by the air bubble to facilitate further separation of the layers. The deep stromal layers are excised, usually in quadrants (see Fig. 4.27.17 ). The intraoperative OCT can aid in determining dissection depth. All viscoelastic material is removed to avoid a dual anterior chamber. A donor button, the same size as the trephination, is then placed after the removal of Descemet’s membrane and the endothelium and secured using 10-0 nylon sutures.


In femtosecond-assisted lamellar keratoplasty (FALK), the donor and recipient are cut with the femtosecond laser, and the donor lenticule can be placed without sutures on the recipient bed ( Fig. 4.27.18 ). Only a bandage contact lens is used in cases when the residual stromal bed is thicker than 250 microns.




Fig. 4.27.18


Femtosecond-Assisted Lamellar Keratoplasty (FALK).

(A) Residual granular dystrophy and central corneal scar seen in a patient after corneal transplantation. When the dystrophy recurred, phototherapeutic keratectomy (PTK) had been performed on the PTK, which eliminated some of the granular deposits but caused some corneal haze. (B) After FALK—FALK was performed to remove the corneal haze and residual anterior granular deposits. FALK (arrowheads) was centered over the visual axis, not over the corneal graft (arrows).

(Courtesy Dr. C. L. Karp.)




Complications and Postoperative Management


In general, anterior lamellar grafts can be very successful (see Figs. 4.27.15 and 4.27.16 ). Complications of ALK are less frequent or less severe in nature compared with those of PKP. Complications of lamellar graft include perforation of the recipient cornea, interface scarring and vascularization, persistent epithelial defect, inflammatory necrosis of the graft and graft melting, infection, astigmatism, and allograft rejection. Careful irrigation and cleaning of the host bed may reduce the incidence of complications. ALK has a significantly reduced incidence of allograft rejection because no transplantation of foreign endothelium is involved.


Perforation of Descemet’s Membrane.


This is a relatively common event early in the surgical learning curve. In small perforations, the case can proceed as planned, but the surgeon should leave a gas bubble (air or SF6 20%) in the eye to ensure that Descemet’s membrane remains attached to the stroma. In larger perforations, a combination of gas and a pass-through suture may be necessary to anchor Descemet’s membrane and avoid its retraction. In larger breaks, conversion to PKP may be required.


Pseudo-Anterior Chamber.


A double anterior chamber may occur when an unrecognized Descemet’s tear occurs, such as during suturing of the donor graft. Moreover, viscoelastic material has been implicated in certain cases. The dual chamber may resolve spontaneously, but most surgeons inject air or SF6 20% in the early postoperative period to enhance recovery times and potential endothelial cell loss.


Triple Procedure (Combined Procedure)


A triple procedure or combined procedure refers to keratoplasty, combined with cataract extraction and IOL implantation.


Preoperative Evaluation and Diagnostic Approach


The triple procedure is indicated for patients with a visually significant cataract who also require corneal transplantation for visual rehabilitation. Triple procedures are increasingly being performed with the use of the DSAEK or DMEK technique for patients with endothelial disease. If visualization permits, cataract extraction may be performed in a closed system by using standard phacoemulsification techniques. The leading indication for a triple procedure is Fuchs’ endothelial dystrophy and cataract, which accounts for up to 77% of eyes that require a triple procedure.


Compared with PKP, a combined procedure requires the additional calculation of the power of the IOL. Different formulas, such as the Holladay or the Sanders–Retzlaff–Kraff formula ( Eq. 4.27.1 ), in which A is the constant for an IOL, AL is the axial length, and K is the keratometric measurement. The determination of K varies from surgeon to surgeon. The authors typically advocate one of two alternative approaches, using either the average of the surgeon’s past postoperative keratometric readings associated with the surgical technique or the K readings from the contralateral eye. In the instances in which an over- or undersized graft is required, +1.00–+2.00 diopters (D) is subtracted from the IOL power for a 0.5-mm oversized graft or +1.00–+2.00 D is added to the IOL power for 0.5-mm undersizing. Postoperative refractive targets must be adjusted in DSAEK or DMEK triple procedures, as there may be a hyperopic shift associated with these procedures.


<SPAN role=presentation tabIndex=0 id=MathJax-Element-2-Frame class=MathJax style="POSITION: relative" data-mathml='IOL power=A−2.5AL−0.9K’>IOL power=𝐴2.5𝐴𝐿0.9𝐾IOL power=A−2.5AL−0.9K
IOL power=A−2.5AL−0.9K


Surgical Techniques


Open Sky Cataract Extraction.


The detailed surgical technique for PKP is described above. Prior to the trephination of the recipient cornea, trypan blue may be considered for visual augmentation of the capsulotomy. After the recipient button has been excised, a capsulorrhexis, sufficiently large to allow subsequent expression of the lens nucleus, is performed. Caution is maintained during the capsulorrhexis because there is a tendency for the capsulectomy to extend peripherally, especially with increased posterior pressure.


After hydrodissection and mobilization of the lens nucleus, the lens is gently expressed. The remaining cortical material is removed carefully using an automated irrigation–aspiration instrument or a manual I/A, as the anterior and posterior capsules tend to collapse toward each other. The capsular bag is then inflated with viscoelastic material, and the appropriate posterior chamber IOL is inserted. The authors of this chapter prefer a rigid or a three-piece IOL in this scenario for increased stability because of anterior chamber fluctuations. If a posterior capsular tear and anterior prolapse of vitreous occur, a limited anterior vitrectomy is performed, and the IOL is inserted either into the ciliary sulcus and sutured to the iris or sclera or an open-loop anterior chamber IOL may be used. The remainder of the procedure for PKP is the same as described previously.


Artificial Cornea (Keratoprosthesis)


Keratoprosthesis implantation is performed in patients in whom corneal transplantation is considered high risk, with a very high likelihood of graft failure, such as those with a history of multiple graft failures or deep neovascularization of the cornea.


Boston K-Pro


The Boston Keratoprosthesis (K-Pro) (formerly known as the Dohlman–Doane Kpro ) has been under development since the 1960s. It received Food and Drug Administration (FDA) approval for commercialization in 1992. It is the most commonly used keratoprosthesis in the world. The keratoprosthesis is made of clear polymethyl methacrylate (PMMA) plastic and has two pieces that take the shape of a collar button. The device is inserted into a corneal graft, which is then transplanted into the recipient’s cloudy cornea. There are two types of the Boston K-Pro: (1) type I, available in phakic and pseudo-phakic versions, is used in patients with an adequate ocular surface, and (2) type II, which is placed through the lids in patients with severe ocular surface disease.


AlphaCor


The AlphaCor implant, approved by the FDA in 2003, is made of a flexible hydrogel material similar to a soft contact lens. It contains a central clear zone that provides refractive power and a peripheral skirt or rim made of a special material that encourages the eye to heal over the device. The device is available in two powers: one for aphakic and one for phakic patients. The two-stage surgery involves the initial implantation of the AlphaCor device into the cornea of the recipient and the creation of a protective conjunctival flap over the prosthesis. The subsequent removal of the flap allows light to pass through the central clear zone to restore vision.


A retroprosthetic membrane can occur following implantation of any artificial cornea and can be removed by using a YAG (neodymium-doped yttrium aluminum garnet) laser, unless highly vascular. Migration of the AlphaCor under the lamellar flap can occur.


Modified Osteo-Odonto-Keratoprosthesis


The osteo-odonto-keratoprosthesis (OOKP) was first described in Italy and documented in 1963 by Benedetto Strampelli and later modified by Giancarlo Falcinelli et al. for the treatment of bilateral corneal blindness in patients with end-stage ocular surface disorders. Falcinelli’s group has completed more than 220 cases, with an anatomical success rate of 94% and a mean follow-up of 9.4 years. The first modified OOKP (MOOKP) was performed in the United States in 2009.


The newer MOOKP consists of a cylindrical PMMA lens embedded within the patient’s own tissue (heterotopic autograft of the patient’s tooth root and alveolar bone). The complete implantation is a three-stage procedure. Initially, the lens, iris, and vitreous are removed from the eye. A portion of the tooth (preferably canine), bone, and periodontal complex is concurrently resected, typically with the assistance of an oral maxillofacial surgeon, and shaped into a thin rectangular lamina. Some surgeons advocate the procurement of the bone lamina from the tibia. The PMMA lens is mounted into the center of the lamina, and the complex is placed into a subcutaneous pocket. After 1–2 months, a patch of buccal mucosa is obtained and sutured over the scarred and vascularized ocular surface. Alternatively, the first two stages may be performed simultaneously. After a minimum period of 3 months, the lamina is retrieved from the subcutaneous pocket. After trephinating appropriately into both the cornea and oral mucosa for the cylindrical lens, the prosthesis is then secured to the surface of the eye between the layers of the scarred cornea and buccal mucosa using absorbable suture ( Fig. 4.27.19 ).


Oct 3, 2019 | Posted by in OPHTHALMOLOGY | Comments Off on Corneal Surgery
Premium Wordpress Themes by UFO Themes