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Superficial Anterior Lamellar Keratoplasty
Mukesh Patil, MBBS, MD, FICO, FAICO; Noopur Gupta, MBBS, MS, DNB, PhD; Murugesan Vanathi, MBBS, MD; and Radhika Tandon, MBBS, MD, DNB, MNAMS, FRCS(Ed), FRCOphth, MNASI
Keratoplasty is a procedure to restore vision in patients who have lost the ability to focus light because of a loss of corneal transparency. Full-thickness penetrating keratoplasty (PK) has been the surgical modality of choice for various corneal pathologies over the past few decades1,2; however, it can be complicated by suture related complications, endothelial rejection with a subsequent possibility of graft failure, and use of long-term topical steroids.
More recently, lamellar keratoplasty has become the procedure of choice in which only affected corneal layers are selectively replaced by healthy lamellar donor tissue. In cases of anterior stromal opacities, anterior lamellar keratoplasty (ALK) targets the replacement of only the anterior stromal tissue preserving the endothelium and thereby obviating the risk of endothelial rejection. Suture-related factors account for 14% to 60% of graft infections, compromising graft survival after the keratoplasty.3,4 These complications have been avoided with the use of human fibrin glue in what have been described as sutureless anterior lamellar keratoplasty.5
Superficial anterior lamellar keratoplasty (SALK), aided by the use of human fibrin glue, can be used in cases of anterior stromal opacities involving less than one-third of the anterior corneal stroma. The main advantages of ALK include decreased incidence of graft rejection, and reduced intraoperative complications associated with the full-thickness open-sky procedures.6 Lately, improvement in instrumentation, surgical techniques, and automation have enhanced the surgical efficiency and visual and anatomical outcomes following ALK surgery. Newer studies have confirmed that the visual outcomes of ALK are comparable to the results of PK.7
TABLE 4-1
INDICATIONS FOR AND CONTRAINDICATIONS TO SUPERFICIAL ANTERIOR LAMELLAR KERATOPLASTY
| INDICATIONS | CONTRAINDICATIONS |
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CLINICAL APPLICATIONS
The indications of SALK include the pathologies limited to anterior one-third of the corneal stroma (Table 4-1), such as in:
- Post keratitis scars (Figure 4-1): Keratitis could heal with either a nebular, macular, or leucomatous opacity. This technique could be very useful for such scars that are limited to the anterior one-third of the stromal depth.
- Post-traumatic scars: Trauma could also result in scars or opacities limited to the anterior layers of the cornea. The aforementioned techniques in such cases could minimize the risk of suture-related complications and provide a quick visual rehabilitation in such cases.
- Salzmann nodular degeneration: The degenerative changes are limited to the superficial layers of the cornea and a SALK comes handy in these cases to restore the vision.
- Epithelial-stromal TGFBI dystrophies (Figure 4-2): The pathology in these cases remains limited to the epithelium or the anterior stroma in depth. The opacities are quite superficial, rendering them easily amenable to SALK.
- Stromal dystrophies (Figure 4-3): Stromal corneal dystrophies present with a varied involvement of the stromal depth. Hence, in cases where the opacities are limited to the anterior one-third of the cornea, this procedure could indeed be useful.
- Trachomatous keratopathy: Trachoma results in opacification of the superficial layers of the cornea resulting in loss of transparency of the cornea and poor quality of vision. SALK in such cases provides an enhanced quality of vision and faster recovery.
- Post–chemical injury scars: Chemical injuries resulting in superficial opacities form another indication for SALK.
- Severe scarring after PRK: An untoward complication of a refractive procedure such as PRK might result in superficial scarring and poorer postoperative visual outcomes. SALK in these cases provides a means of rescue to restore vision.
- Recurrent epithelial ingrowth after laser in situ keratomileusis8,9: Epithelial ingrowth with flap necrosis following LASIK procedure could, in rare and severe cases, require SALK following flap amputation.
- Stromal dystrophies (Figure 4-3): Stromal corneal dystrophies present with a varied involvement of the stromal depth. Hence, in cases where the opacities are limited to the anterior one-third of the cornea, this procedure could indeed be useful.
Figure 4-1. Post-keratitis scar.
Figure 4-2. Epithelial-stromal TGFBI dystrophy.
Figure 4-3. Stromal dystrophy.
CONTRAINDICATIONS
The contraindications to SALK include the following:
- Deep scars involving more than one-third of anterior corneal stroma: Deeper scars are not amenable for dissection by superficial keratoplasty and may instead require either a deep lamellar or a full-thickness PK.
- Corneal endothelial disorders: As has been previously mentioned, a healthy endothelium is a prerequisite for any superficial keratoplasty procedure. In cases with a compromised endothelium, it is advisable to proceed with full-thickness PK.
- Uncontrolled glaucoma: Raised intraocular pressure (IOP) interferes with healing of the graft and can result in the primary failure of the graft.
- Active uveitis: Uveitis causes inflammation and can result in a failed graft.
- Ocular surface disorders: Dry eye disease and lid abnormalities, such as entropion, ectropion, and trichiasis, can result in failure of the graft by interfering with the healing process or causing recurrent breakdown of the tear film. Thus, the presence of any ocular surface abnormality is a relative contraindication for performing SALK until it is treated first.
- Eyes with small palpebral aperture, deep-set eyes: Eyes with small palpebral aperture and deep-set eyes pose difficulty in fitting of the microkeratome head over the host bed and thereby cause problems in preparation of the host bed.
- Systemic conditions like uncontrolled diabetes, collagen vascular disease, and immunocompromising conditions: These conditions can impair healing and uptake of the graft and hence systemic optimization is mandatory before any surgical procedure is planned in such cases.
ESSENTIALS OF SURGICAL TECHNIQUE
Preoperative Evaluation
It is indeed important to do a thorough preoperative evaluation before planning a patient for SALK. This includes a holistic elicitation of history as well as clinical examination. The history is important to know the exact nature and, if applicable, inheritance pattern of the pathology. The important aspects include any use of ocular or systemic medications, previous ocular surgery, occupation, and visual demands. It is also important to explain realistically the visual and anatomical outcomes and associated complications.
The systemic history and examination are important to rule out the presence of any collagen vascular diseases, diabetes mellitus, or any other immunocompromising conditions that might pose a difficulty for the survival of the graft.
The preoperative ocular examination includes the following:
- Visual acuity: Both the uncorrected and best-corrected visual acuity are to be noted. This could be done with the Snellen’s, ETDRS (Early Treatment Diabetic Retinopathy Study), or logMAR visual acuity charts. Refraction and contact lens trial should be done wherever possible.
- External eye examination: Ocular surface and ocular adnexa should be thoroughly examined to look for the presence of any dry eye disease, entropion, ectropion, lagophthalmos, and trichiatic eye lashes. It is pertinent to rule out these pathologies as these could lead to delayed epithelialization and in turn decreased survival of the graft.
- Slit lamp biomcroscopy: Slit lamp examination includes the assessment of the tear film, the extent and depth of opacity, any other previous surgical scars, iris and lens status, and also the status of endothelium, as unhealthy endothelium precludes the possibility of ALK and in such cases a full-thickness PK should instead be planned.
- Assessment for dry eye: Tear film assessment is very important as healthy ocular surface is the key to the healing and survival of the graft. Tear film examination includes the tear film breakup time and the Schirmer’s test.
- IOP: IOP should be measured preoperatively, and all measures should be taken to reduce the high IOP so as to allow timely epithelialization and healing of the graft.
- Visual potential: Preoperative assessment of the visual potential is recommended to aid in prognostication as the opacities may sometimes be long standing since early childhood, with the possibilities of preexisting amblyopia. The chances of postoperative visual gain in such cases are bleak. This includes a thorough fundus examination to rule out any comorbid retinal pathology. Other tests that could be done to assess visual potential are laser interferometry or potential acuity meter.
Special Investigations
Anterior Segment Optical Coherence Tomography
Anterior segment optical coherence tomography (ASOCT) helps to clearly find out the depth of opacity and is the most important tool in planning the surgery.
Pachymetry
The corneal thickness could be measured with either the optical or ultrasonic pachymetric methods. This measurement helps us to avoid inadvertent surgery and complications in cases of thinner corneas.
Specular Microscopy
Specular microscopy should be done to find out the status of host endothelium, as it is the prerequisite for performing ALK.
Confocal Scan
Confocal scan is an alternate tool that can help to assess the host endothelial status and to ascertain the depth of involvement.
Topography
The topographic analysis of the cornea is important to rule out any concurrent ectatic corneal disorder.
Surgical Technique
SALK can be done under local or general anesthesia depending on patient’s age and cooperation. Various techniques of SALK are as follows:
- Microkeratome-assisted SALK
- Hemiautomated SALK
- Femtosecond laser–assisted SALK
Preparation of Host Bed
The host lamellar bed can either be prepared with microkeratome and the suction ring, superficial manual dissection, or the femtosecond-assisted dissection as has been mentioned previously. The advancement of the microkeratome over the suction ring can either be fully automated (ALK System; Figure 4-4) or be manually assisted (Gebauer Medizintechnik GmbH; Figure 4-5). The microkeratomes are available with different heads in which various ranges of blades can be fitted depending upon the desired depth of the cut. The aim of this maneuver is to cut a superficial corneal lamella with the same diameter and thickness as the donor tissue.
Dissection of superficial diseased host tissue can be done manually with the help of diamond knife and crescent blade (Figure 4-6). The host bed is then washed with balanced salt solution (BSS) to remove any overlying debris. Never discard the dissected lamellar host tissue and keep it safely under aseptic conditions until surgery is over.
Figure 4-4. (A, B) Preparation of host bed with fully automated microkeratome (ALK System).
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