After corneal surgery, contact lenses may be indicated to provide improved optical correction or therapeutic ocular surface protection. Optical indications include the correction of irregular or high regular astigmatism, secondary aniseikonia and the correction of refractive error to eliminate spectacle correction ( ). For those with induced anisometropia, restoration of binocular vision may be achieved with contact lenses. When there is induced irregular astigmatism, contact lenses, specifically rigid lenses, may provide the only option for visual rehabilitation ( ). Rigid lenses are able to correct the residual refractive error and reduce the total higher-order aberrations to more normal levels ( ). Contact lenses can be used as a therapeutic option in post-keratoplasty (KP) for cases of persistent epithelial defect or loose sutures (Jacobs et al., 2001; ) (see Chapter 28 ).

Fitting and prescribing contact lenses for patients following corneal surgery can be both extremely rewarding and challenging. Expectations may be high, since patients are typically seeking improvement in the postoperative visual outcome along with good contact lens comfort. Some patients may be frustrated and impatient if the initial surgery did not meet their expectations. Contact lenses may have been previously tried without success or with limited success. Restoring comfortable functional vision while maintaining improvements from the surgery is potentially life altering and can improve the quality of life. Corneal surgeries may be divided into three categories: refractive surgeries, corneal collagen crosslinking (CXL) and corneal transplantations.

Refractive Surgery

The number of different refractive surgical procedures continues to grow. Previous and current procedures are listed in Table 29.1 . Each of these procedures modifies the corneal surface in a unique way, necessitating a rethinking of traditional lens designs and fitting techniques for optimal contact lens performance. The popularity of radial keratotomy (RK) has declined since the approval of the excimer laser in 1995 due to the improved outcomes from photorefractive keratotomy (PRK) and laser-assisted in situ keratomileusis (LASIK) ( ). LASIK continues to be the most well-known and most widely performed technique ( ). In the United States, LASIK surgeries have declined from 1,034,000 in 2008 to 718,000 in 2020. This number is expected to rise again in the near future ( ). Successful refractive surgery, patients with myopia, hyperopia and astigmatism can reduce or eliminate their dependence on glasses and contact lenses ( ).

Table 29.1

Types of Refractive Surgery

Incisional Laser Other
Radial keratotomy (RK) Photorefractive keratectomy (PRK) Keratophakia
Astigmatic keratotomy (AK) Laser-assisted in situ keratomileusis (LASIK) Keratomileusis
Limbal-relaxing incisions (LRI) Laser-assisted sub-epithelial keratomileusis (LASEK) Epikeratoplasty
Corneal-relaxing incisions (CRI) Laser thermokeratoplasty (LTK) Thermokeratoplasty
Phototherapeutic keratectomy (PTK) Small-incision lenticule extraction (SMILE) Conductive keratoplasty (CK)
Ruiz procedure Femtosecond laser-assisted in situ keratomileusis (Femto-LASIK) Automated lamellar keratoplasty
Femtosecond laser lenticule extraction (FLEx) Intrastromal corneal ring segments (ICRS)
Combination PRK/corneal collagen crosslinking CXL Corneal allogenic intrastromal ring segments (CAIRS)

Contact Lens Fitting Following Refractive Surgery

Contact lens fitting differs between incisional and laser procedures.

There are three main indications for fitting contact lenses following photorefractive procedures:

  • bandage lenses in the immediate postoperative period following epithelial debridement or the creation of a corneal flap, PRK, LASIK and laser-assisted sub-epithelial keratomileusis (LASEK), where the epithelium is removed during the procedure to promote epithelial healing, preserve flap integrity and relieve pain ( )

  • for ametropia following undercorrection or overcorrection

  • to correct irregular corneal astigmatism, which may have been preexisting, induced during surgery, or due to postsurgical ectasia.

Additionally, after incisional procedures:

  • There are greater changes in the mid-peripheral cornea.

  • Fewer soft contact lens designs can be used owing to the presence of perilimbal incisions.

  • The cornea may have elevated mid-peripheral pivot points secondary to incisional wound healing. These areas are the major cause of corneal lens decentration.

  • There is more diurnal fluctuation in visual acuity because of the instability of the peripheral cornea. This is especially important if soft contact lenses are used.

  • When radial incisions are placed into the mid-peripheral cornea, the wounds gape open under the force of the intraocular pressure and stresses form within the corneal tissues ( Fig. 29.1 ). The gaping incisions are first filled with an epithelial plug, which is eventually replaced by a permanent wedge of fibroplastic scar tissue ( Fig. 29.2 ). This results in an overall increase in corneal surface area, although the corneal diameter remains unchanged.

    Fig. 29.1

    Wound gape created by symmetrically placed radial incisions.

    Fig. 29.2

    Wedge-shaped fibroplastic scar in a healed radial incision (cat eye).

The degree of wound gape and the resultant amount of corneal flattening are dictated by a number of surgical and biological factors, including the following:

  • the number, depth and length of the incisions

  • intraocular pressure forces

  • stresses and biochemical properties within the corneal tissue

  • patient age at the time of surgery

  • individual wound-healing responses.

The main indications for contact lens fitting after refractive surgery are as follows:

  • mechanical corneal warpage ( )

  • corneal neovascularization ( )

  • flap dislocation ( )

  • keratectasia ( )

  • dry-eye syndrome ( )

  • corneal neuralgia ( ).

Severe complications following refractive surgery are rare; however, cases and case series have been reported after PRK, LASIK and LASEK ( ). It is challenging to determine if these complications are caused by the surgical procedure, due to therapeutic lens wear or a combination of both ( ).

Radial Keratotomy

RK has largely been phased out in favour of more sophisticated and predictable laser surgical procedures. Although RK and astigmatic keratotomy are infrequently the primary surgical procedure for myopia and astigmatism, they are still used in conjunction with other refractive and surgical techniques ( ). However, there are many in the contact lens practice who had RK performed within the past 30–40 years ( ) and now they may have presbyopia and suffer from overcorrections ( ), hyperopic shifts ( ) and diurnal variations ( ). According to the prospective evaluation of RK study, a shift of the refractive error in the hyperopic direction continued 10 years after surgery ( ). An understanding of the difficulties in fitting the post-RK cornea is still required for the contact lens management of these patients as it poses far greater challenges than those encountered after other refractive procedures.

There is a common misconception that the mid-peripheral cornea steepens following RK. However, as the anterior cornea displaces to accommodate the gaping incisions, virtually the entire cornea from limbus to limbus flattens. The flattening effect is simply greater in the central cornea than in the periphery, resulting in the false impression of mid-peripheral steepening.

The cornea is malleable and prone to warpage during a period of up to 3 months following RK ( ). It is not advised to commence a contact lens fitting during the first three months unless it is medically necessary.

Phototherapeutic Keratectomy

Phototherapeutic keratectomy is a surgical therapeutic treatment to manage various corneal conditions that uses a medical device called an excimer laser, with the control of a computer to remove a small outer layer of diseased tissue from the cornea. The precision of the procedure leaves the surrounding area with very little trauma. After removing the damaged layer, new tissue is left, which will naturally restore over the newly smoothed surface area. Once the procedure is complete, a contact lens bandage is placed to allow adequate healing and to reduce any pain or discomfort felt. Antibiotics and prescription eye drops will be prescribed and are an important element of the recovery process.

Photorefractive Keratectomy, Laser-Assisted In Situ Keratomileusis and Laser Epithelial Keratomileusis

Irregular astigmatism is a relatively rare finding after either PRK or LASIK. However, it may be induced by the creation of a suboptimal lamellar flap – too thin, irregular, bisected, buttonholed or a free flap, or due to postoperative ectasia. Flap striae are another important and often underrecognized cause ( ). Irregular astigmatism can also arise from a decentred ablation. Patients are often left with varying degrees of uncorrected myopia due to the eccentric position of the treatment zone away from the visual axis. Viewing through the edge of the ablation frequently results in a loss of best corrected visual acuity (BCVA), monocular diplopia and ghosting of distance images, especially under scotopic conditions. The severity of symptoms often correlates with the size of the pupil. A decentred ablation with a large 6–7 mm pupil will produce more serious visual complaints than does a similarly displaced ablation over a small 3–4 mm pupil. Soft contact lenses rarely provide adequate optical correction in this small subset of patients. Optimal visual performance usually requires the use of a rigid lens design.

Refractive surgery techniques are moving forward with the introduction of femtosecond lasers. These create LASIK flaps with better accuracy, uniformity and predictability than do mechanical microkeratomes ( ). The higher-frequency femtosecond platforms elicit less inflammation and provide better visual outcomes. Small-incision lenticule extraction (SMILE) is another procedure made possible by femtosecond lasers and achieves similar safety, efficacy and predictability to LASIK with greater preservation of corneal nerves and biomechanical strength ( ). Hopefully, in the future, advancing diagnostic capabilities and surgical techniques will reduce the need for postrefractive surgery contact lens fitting.

Corneal Collagen Crosslinking

Soft bandage contact lenses are routinely used with epithelium removal (epi-off) CXL to promote epithelial healing and reduce postoperative pain ( ). The risk of infection with bandage contact lenses after CXL is very low ( ). Steroids used concomitantly with BSCL was the largest risk factor for infection after surgery ( ). The increased risk of infection post CXL is higher than in PRK. The authors suggest that the higher incidence of atopy among patients with keratoconus compared to those undergoing refractive surgery may be contributory ( ). evaluated the use of bandage contact lenses and reepithelialization after CXL with balafilcon A and hioxifilcon A lens materials. There was complete healing of the epithelium by day three; there were not any differences in pain control.

Corneal Transplantation

Corneal transplantation or KP is a surgical procedure by which diseased corneal tissue is removed and replaced by donor material (a corneal graft) ( Fig. 29.3 ). Table 29.2 presents the lexicon of various KP procedures.

Fig. 29.3

A penetrating keratoplasty with interrupted sutures and subconjunctival haemorrhage.

Courtesy Tom Arnold.

Table 29.2

Types of Corneal Transplantation

Incisional Laser
Penetrating keratoplasty (PKP) Femtosecond laser-assisted keratoplasty (FLAK)
Anterior lamellar keratoplasty (ALK) Femtosecond laser-assisted Descemet membrane automated endothelial keratoplasty (fDMAEK)
Deep anterior lamellar keratoplasty (DALK)
Endothelial keratoplasty (EK)
Deep lamellar endothelial keratoplasty (DLEK)
Descemet stripping endothelial keratoplasty (DSEK) Femtosecond laser-assisted corneal transplant (FACT)
Descemet stripping automated endothelial keratoplasty (DSAEK)
Pre-Descemet stripping endothelial keratoplasty (PDEK)
Descemet membrane endothelial keratoplasty (DMEK)
Descemet membrane automated endothelial keratoplasty (DMAEK)
Hemi-Descemet membrane endothelial keratoplasty (Hemi-DMEK)
Keratolimbal allograft transplantation (KLAL)

Corneal transplantation resulting in relatively clear grafts was first reported in the ophthalmic literature with Reisinger’s rabbit experiments ( ). Such homografts (or allografts) are transplants within the same species (i.e. from one rabbit to another or from one human to another) and are the most common form of KP. made several unsuccessful attempts to graft a glass prosthesis, but his work forms the basis of modern KP. , and others also used animal corneas as donors for humans: these are heterografts – transplants from one species to another – and are commonly rejected ( ). is credited with the first human corneal transplant (treating a leukoma due to a quicklime burn) to retain a moderate degree of transparency. The introduction of McCarey–Kaufman medium ( ) enabled donor human cornea to be stored for 3–4 days. Further advances based on tissue culture techniques extended the preservation of donor tissue for up to 30–40 days ( ). Autografts, wherein one eye provides the donor cornea for the other, although rare for obvious reasons ( Fig. 29.4 ), have limited, if any, risk of rejection. An artificial corneal graft, such as the Boston Keratoprosthesis (KPro), is the most widely used artificial cornea or KPro. This is a treatment option for corneal disease not amenable to standard KP ( Fig. 29.5 ) ( ).

Fig. 29.4

Corneal autograft. This patient had congenital syphilis and when the cornea of her good eye failed, it was grafted with a donor button taken from her contralateral, severely amblyopic eye (to enhance her chances of avoiding rejection) and that donor replaced with a traditional allograft.

Fig. 29.5

Dohlman keratoprosthesis; note the bandage soft lens in place (by the bubbles seen in the 3/9 zones).

Approximately 35,000–51,000 KP procedures were performed annually in the United States over the past two decades ( ). In 2019, 51,336 intermediate-term preserved corneas were transplanted in the United States and 28,402 were exported internationally ( ). Another 2000+ per year over the last decade in the United Kingdom ( ) and another 2000 in Australia ( ). With the introduction of enhanced lamellar KP (LK) techniques, this number appears to be increasing in all three areas.

Indications for Corneal Transplantation

Corneal grafts are performed for the following reasons:

  • optical – to restore visual function by removing scarred or irregular tissues (e.g. in keratoconus, post trauma and infection, corneal dystrophy)

  • therapeutic – to treat disease (e.g. to treat an infection by debulking)

  • tectonic – to restore, or preclude the loss of, globe integrity

  • cosmetic – to improve appearance (e.g. eliminate an un-sightly scar in a nonseeing eye). The outlined indications above are not necessarily mutually exclusive.

The diagnostic indications for corneal grafts include:

  • corneal oedema that is severe enough to affect visual function and painful bullous keratopathy, usually a consequence of Fuchs’ endothelial dystrophy or aphakic/pseudophakic endothelial failure

  • keratoconus and other forms of corneal ectasia such as pellucid marginal degeneration and Terrien’s degeneration. The criteria for performing KP may be when the condition is severe enough to limit vision with contact lens correction to 6/12 or worse, or when contact lens wear can no longer be tolerated for physical or physiological reasons. Approximately 12–20% of keratoconic patients may require and benefit from corneal transplantation ( ).

  • corneal scars and interstitial keratitis, secondary to trauma and/or infection (e.g. herpetic keratitis)

  • visually debilitating forms of corneal dystrophy, such as the transforming growth factor beta 1 dystrophies (e.g. granular I or II, lattice or Reis–Bücklers) and macular corneal dystrophy

  • congenital opacities, such as Peters’ anomaly or buphthalmos secondary to congenital glaucoma

  • previous graft rejection or failure.

Types of Corneal Transplantation

Penetrating Keratoplasty

Full-thickness penetrating KP (PKP), first using mechanically paired blades to produce square grafts but evolving to circular grafts produced with trephines, has been the standard of care in corneal transplantation for more than 50 years. Patch grafts have long been used to seal corneal leaks, but visual results are not important. Corneal transplantation techniques are rapidly evolving ( ). The traditional full-thickness PKP performed with a trephine is becoming less conventional, while LK is becoming a surgery of choice in patients with corneal disease or opacity that spares the endothelium ( ).

Irregular Corneal Topography After Penetrating Keratoplasty

The main optical challenge following traditional PKP [perhaps lessened but not eliminated with the advent of femtosecond laser-assisted corneal transplant (FACT) and other forms of anterior LK (ALK)] has been irregular surface astigmatism ( Fig. 29.6 ). Optical rehabilitation of these distorted corneas remains a principal function of specialty contact lens practice, and PKP remains, despite the growth in the LKs, a common patient presentation. Hence, care of this disease will be discussed in depth in this chapter. It should also be noted that according to : ‘after successful Descemet’s membrane endothelial keratoplasty (DMEK), 23 of 262 eyes (9%) showed subnormal spectacle [corrected vision] and/or monocular diplopia due to corneal scarring, surface irregularities or undetectable optical imperfections that could be managed by contact lens fitting. Prolonged preoperative corneal edema for more than 12 months may be a risk factor for diffuse irregular astigmatism after DMEK …’.

Fig. 29.6

Irregular surface astigmatism in a graft, as indicated by the distorted reflex of a perfectly circular flash gun.

Courtesy Desmond Fonn, Bausch & Lomb Slide Library.

documented the prevalence of the various forms of corneal topography following trephine PKP as: ‘prolate’ (30%), ‘oblate’ (30%), ‘mixed’ (20%), ‘asymmetric’ (10%) and ‘steep to flat’ (10%). discussed these corneal topographic outcomes in more clinically descriptive terminology as: ‘nipple’ or steep; ‘proud’, whereby the graft is totally or partially elevated above the host corneal surface ( Figs. 29.7 and 29.8 ); ‘sunken’, whereby the graft is depressed below the host surface; and ‘tilted’ or ‘eccentric’. These outcomes are illustrated in Fig. 29.9 .

Fig. 29.7

Proud graft totally elevated above the host corneal surface in a keratoconic eye.

Courtesy Robert Terry, Bausch & Lomb Slide Library.

Fig. 29.8

Protruding graft post-PK in a keratoconic eye.

Courtesy Melissa Barnett.

Fig. 29.9

Graft profiles.

Adapted from Phillips, A. J. (1997). Postkeratoplasty contact lens fitting. In M. J. Harris (Ed.), Contact lenses for pre- and post-surgery (pp. 97–132). St Louis, MO: Mosby.

suggested that causes of these topographic outcomes include:

  • suboptimal cutting of the donor, the host or both

  • eccentric placement of the graft

  • elevation of the graft edge during healing, with poor wound approximation

  • loosening of sutures

  • localized abnormal healing

  • initial corneal irregularity (e.g. keratoconus).

Lamellar Keratoplasty

Epikeratoplasty – a short-lived surgical procedure – was this early LK variant wherein a precut (to a specific optical power) donor cornea was applied to the anterior surface of the intact host stroma (the epithelium but not the stroma was removed) in an effort to address aphakia, keratoconus or high myopia. It was found to result in poor vision (secondary to interface problems) and has been abandoned.

Superficial corneal diseases have long been alternatively treated with ALK wherein, following initial partial-thickness trephination, a blunt blade was used mechanically to separate a deep plane in the tissue to allow replacement of only the diseased superficial cornea. ALK retains the host endothelium to thereby reduce both immunological rejection and physiological failure. ALK optical results were poor, however, were usually reserved for either the corneal periphery or as tectonic procedures later followed by PKP to allow optical rehabilitation.

Several endothelial LK procedures to replace only damaged posterior corneal tissues (as in Fuchs’ dystrophy) have evolved. Deep ALK (DALK) and endothelial KP (EK) are the two main subcategories of LK. The purpose of most types of LK is to maintain as much of healthy, functional tissue of the cornea and remove the diseased portion of the cornea.

DALK is a newer LK that utilizes air, water or a microkeratome to separate the deep stromal fibres from Descemet’s membrane to replace unhealthy stroma, while the recipient corneal endothelium and Descemet’s membrane are retained ( ). DALK is used for corneal conditions that do not involve the corneal endothelium, such as a stromal scar. It is thought that deepening the position of the interface between the replacement and host cornea improves the potential visual results; DALK has gained some popularity owing to its theoretical advantages, in treatment of keratoconus in particular, although its practical superiority to PKP remains in question ( ).

EK has replaced PKP as the preferred surgical treatment for endothelial disorders such as Fuch’s endothelial dystrophy and bullous keratopathy ( ). In EK, the diseased Descemet’s membrane, including the endothelium, is stripped from the recipient posterior stroma ( ). Next, the donor tissue is transferred into the anterior chamber, unfolded and attached to the recipient stroma using an air bubble without the use of sutures ( ). Corneal integrity is improved since the anterior corneal surface is not affected by surface incisions and sutures. Wound-healing issues and suture-related complications are reduced. Faster and more comprehensive visual rehabilitation may occur with spectacle correction only since significant refractive error changes are avoided ( ).

In advanced corneal disease, such as long-standing corneal oedema and significant anterior stromal scarring, visual outcomes may be affected by surface irregularities after EK such as subepithelial stromal scarring, collagen disorganization and subepithelial fibrosis ( ). Contact lenses may be used to correct reduced vision and reduce monocular diplopia and ghost images ( ).

The rate of EK surgery has continued to rise in the United States. In the past 10 years, EK procedures have increased from 1308 in 2010 to 30,650 in 2019 ( ). After the corneal graft is performed and the cornea is clear, corneal topography or corneal tomography and spectacle refraction will help guide the choice of contact lens design.

Subcategories of EK include deep lamellar EK (DLEK) ( ), Descemet’s stripping membrane EK (DSEK) ( ), or an automated version using a microkeratome called Descemet’s stripping automated membrane EK (DSAEK) ( ) and DMEK ( ), wherein only the endothelial layer is replaced ( Fig. 29.10 ). DSAEK is currently the most prevalent procedure where the donor tissue is comprised of Descemet’s membrane, endothelium and an added thin layer of posterior stroma ( ). In general, visual acuity with DSAEK is better than PKP; however, the layer of attached stroma in a DSAEK procedure may reduce visual acuity, so there are fewer cases that obtain vision better than 20/25 ( ). In DMEK, the goal is to leave the host anterior corneal surface smooth and intact so that patients may not require contact lens correction ( ). DMEK in particular mitigates the two principal liabilities of KP: immunological graft reactions ( ) and secondary glaucoma from prolonged topical corticosteroid use ( ).

Fig. 29.10

A cornea post-Descemet’s stripping endothelial keratoplasty (for treatment of the combination of iris naevus or Cogan–Reese syndrome; Chandler’s syndrome; and essential iris atrophy, called ICE syndrome). Note increased corneal thickness extending into the anterior chamber seen in the optical section superiorly.

DLEK, DSEK, DSAEK and DMEK, each more technically demanding than its predecessor, theoretically also offer rapid healing, more acceptable refractive outcomes and better retention of corneal strength, compared with PKP – but surgery is technically very demanding and donor adherence may be challenging. With increasing optical success of DSEK, DMEK and DALK, and selectively targeting diseased corneal tissue with lamellar surgery, PKP has lost its position as the sole dominant KP technique over the past decade ( ). The discussion about which procedure may prove optimal for many patients continues ( ).

No modern discussion of KP, however, would be complete without a discussion of artificial corneas. Though viable artificial cornea materials and surgical procedures have long been sought so as to address insufficient human transplant material, immunology and religious concerns, only recently has this become a practical reality ( ); several competitive designs may shortly be available ( ).

IntraLase-Enabled Penetrating Keratoplasty

Development of the IntraLase femtosecond laser allows corneal surgeons to create complex, shaped PKP incisions (e.g. ‘top hat’, ‘mushroom’, ‘zigzag’) that are identical in both host and graft tissue. Called IntraLase-enabled KP (IEK or ‘FACT’), this procedure creates PKPs with customized ‘interlocking’ – edge designs that it is hoped will minimize induced astigmatism and enhance wound strength. The risk for displacement of the graft may also be reduced. Fewer sutures are required, improved wound-healing time and decreased regular and irregular astigmatism will hopefully enhance vision and expedite contact lens fitting after femtosecond laser-based full-thickness KP than with previous techniques. A study of 116 keratoconus patients found that the 56 patients treated with IEK had significantly better vision improvement than did those receiving traditional trephine PKP: 3 months postoperatively, significantly more IEK patients were reported to have better best spectacle-corrected visual acuity ( P = .001) and visual recovery 20/40 or better ( P <.001) and lower topographic astigmatism ( P = .001) ( ). An earlier large study had reported a lower (30%) improvement in 2800 patients treated with traditional trephine PKP ( ).

Suture Techniques for Penetrating Keratoplasty

Contact lens practitioners should have a general appreciation of suture techniques used for PKP because patients commonly present for fitting or aftercare visits with some or all sutures still in place. Sutures may be of the following forms:

  • running (or continuous) – a continuous suture forms a zigzag pattern across the host–graft interface, which extends around the full circumference of the graft ( Fig. 29.11 )

    Fig. 29.11

    A penetrating keratoplasty with a single running suture.

    Courtesy Carina Koppen.

  • double running – two continuous sutures form a zigzag pattern across the host–graft interface, which extends twice around the full circumference of the graft

  • interrupted – a number of single sutures, commonly 12 or 16, which are equally spaced around the graft circumference (see Fig. 29.12 )

    Fig. 29.12

    A penetrating keratoplasty with interrupted sutures.

  • combination – both running and interrupted sutures are used.

These various forms of suturing are illustrated in Fig. 29.13 . Most surgeons use either double running or one running and several interrupted sutures as the technique of choice. Square grafts (common many years ago) are rarely, if ever, performed currently. When occasionally seen, they must be followed. In a prospective study, astigmatism was found to be the least following double running sutures compared with interrupted or single running sutures 18 months after PKP ( ). At some point – commonly some 3–6 months after surgery – either one running suture or the interrupted sutures are removed, often selectively in an effort to moderate astigmatism. One running suture or several interrupted sutures are commonly left in place indefinitely, only to be removed if problems or breaks develop. Interrupted sutures alone are favoured when PKP is attempted in the face of active anterior-segment inflammation or corneal neovascularization to permit later individual removal when appropriate. Adjunctive surgery, relaxing incisions, additional sutures or even wedge resection procedures have been used with variable success to address postoperative astigmatism ( ).

Fig. 29.13

Grafts and sutures.

Contact Lens Fitting Following Keratoplasty

The indications for contact lens use following corneal grafts are primarily postoperative irregular or high astigmatism and secondarily anisometropia (e.g. as will occur in aphakia). In addition to visual acuity improvement, contrast sensitivity is also enhanced with corneal lenses ( ). Between 20% and 60% of trephine-cut post-PKP patients benefit optically from contact lens wear ( ). In patients with keratoconus that undergo PKP, between 31% and 56% return to contact lens wear after surgery ( ).

Contact lens contraindications include:

  • a good (or even adequate) visual result with spectacle correction alone

  • anticipated poor compliance with contact lens care.

Relative contraindications (most of which increase both risks of infection and those of rejection) include:

  • decreased corneal sensitivity – expected during the first year postoperatively ( )

  • dry eyes – tear break-up time was found to be significantly shorter 3 and 12 months after KP ( )

  • blepharitis

  • dacryocystitis.

Contact Lens Modalities

Soft Lenses

Conventional Soft Lenses

Soft contact lenses emerged in the early 1970s with the creation of cross-linked hydrogel polymers and the introduction of hydrogel contact lenses ( ). Conventional hydrogel lenses fail to meet the Holden and Mertz criteria (87.0 Dk / t ) to provide the cornea with enough oxygen to avoid excess corneal swelling during overnight wear ( ). Some conventional hydrogel lenses do not provide the cornea with enough oxygen (24.1 Dk / t ) to avoid excess corneal swelling during daily wear ( ). Hypoxia complications include corneal oedema, corneal endothelial cell damage, corneal neovascularization and bulbar injection ( ). Silicone hydrogel contact lenses have reduced likelihood corneal hypoxia ( ).

Compared to hydrogel lenses, silicone hydrogel lenses are not associated with improved comfort ( ) nor reduced frequency of microbial keratitis ( ). Limited well-controlled studies related to silicone hydrogel materials being used specifically for medical purposes are present in the literature (Jacobs et al., 2001).

Bandage Lenses

Bandage lenses are used in the immediate postoperative period to relieve pain and to assist in re-epithelization following PRK and LASEK. These procedures involve removal of the corneal epithelium. The corneal surface needs between 2 and 4 days to regenerate, so lenses are typically worn continuously for 3–5 days following surgery to mitigate pain and promote reepithelialization ( ). Managing the wound-healing response is critical for a successful outcome to ensure re-epithelization occurs quickly, thereby reducing stromal haze ( ). This is best achieved with lenses of high Dk / t , for increased corneal oxygenation. Lens fit and corneal shape impacted comfort for managing postoperative pain in PRK. In a prospective study eyes were fit with a silicone hydrogel lens in two base curves: 8.4 and 8.8 mm ( ). Corneas with a postoperative keratometry (K) value of less than 38 dioptres had better pain outcomes with the 8.8 mm base curve. Steeper corneas with a postop K value greater than 42 dioptres did better with the 8.4-mm lens. Lens fit, in contrast to lens material or Dk, is important in bandage contact lens selection after PRK.

Many studies have been carried out to assess the relative benefits of different silicone hydrogel lens materials and designs when used as bandage lenses ( ). All found no major clinical difference between the lenses, although patients reported greater comfort with senofilcon A lenses. concluded that factors other than oxygen permeability affect pain and epithelial healing.

Bandage hydrogel contact lenses are also sometimes used as drug delivery devices or to treat nonhealing epithelial defects in the immediate postoperative period and for wound dehiscence at any time ( ) ( Fig. 29.14 ). Bandage soft lenses are also used both for protection (e.g. dehydration) and for optical ‘smoothing’ over the Dohlman KPro artificial cornea ( ).

Fig. 29.14

A bandage hydrogel lens used 1 day after surgery to cover a graft that has been secured with interrupted sutures.

Drug Delivery

Soft contact lenses for ophthalmic drug delivery may be used to allow extended wear and increased bioavailability. The use of contact lenses as ocular drug delivery systems has been considered intuitive for decades ( ). At the time of publication, a single approved product became available. Johnson & Johnson Vision Acuvue Theravision with Ketotifen contains ketotifen, an H1 histamine receptor antagonist for the prevention of itch associated with eye allergies as the first and only vision correction contact lens that relieves allergic eye itch ( ).

Following Refractive Surgery

With myopic ablations, the mid-peripheral cornea (beyond the central 6.0–7.0 mm) remains unchanged. Therefore the major concern in fitting soft or corneal contact lenses is the relative difference between the flatter central cornea and the steeper (normal) mid-peripheral cornea. This difference creates few problems for patients who had low to moderate myopia prior to surgery. In such cases, the small amount of tissue ablated does not noticeably affect the contact lens fit or the on-eye lens dynamics. Most of the currently available daily disposable or frequent-replacement soft lenses are viable options for the postlaser correction. However, after surgery a complex relationship exists between visual acuity, defocus (refractive error), diffraction and optical aberrations. The loss of postoperative central corneal asphericity can result in a form of spherical aberration ( ). Patients with large pupils may be symptomatic. Improved optical correction can be achieved with soft lens designs that incorporate aberration-correcting anterior aspheric optics.

Radial Keratotomy

In principle, the fitting of a soft contact lens to a cornea that has undergone RK is very similar to fitting a normal cornea. The back optic zone radius (BOZR) will usually need to be approximately 0.5 mm greater than the flattest keratometry reading. However, in most cases a BOZR of greater than 9 mm will be required to achieve satisfactory alignment with the post-RK cornea, therefore the soft lens will need to be custom made. Disposable lenses will be a possibility only when the amount of central flattening (and subsequent negative asphericity) is of a relatively low degree ( ). It must be remembered that even toric soft lenses will not neutralize the irregular corneal astigmatism that often occurs as a result of RK.

Incisional neovascularization is a common complication associated with the use of soft contact lenses following RK, especially when the incisions reach the limbus ( ) ( Fig. 29.15 ). Its incidence can be minimized through the use of high-oxygen-permeability silicone hydrogel lenses used on a daily-wear basis.

Fig. 29.15

Incisional neovascularization secondary to the wearing of a low-water-content soft contact lens.

Penetrating Keratoplasty

Hydrogel contact lenses, both standard and in custom parameters, may be occasionally helpful, especially for the following situations:

  • high refractive errors with lesser degrees of astigmatism•rigid lens intolerance•acceptance of a less than optimal visual result

  • protection of KPro [the KPro produced by ].

Hydrogel lenses include both nonsilicone and silicone hydrogels, the latter offering enhanced corneal oxygen supply, which theoretically should be advantageous to a cornea following a corneal graft from a physiological perspective.

Soft Lenses Over Keratoprosthesis

The function of a contact lenses over KPro is to protect the corneal tissue that surrounds to the anterior plate of the KPro, maintain hydration to prevent desiccation, avert epithelial breakdown, dellen formation and corneal melt ( ). In a multivariate analysis, eyes that had soft contact lenses removed or lost without replacement were more likely to develop complications ( ). Surface deposits on soft contact lenses may impair BCVA ( ). Hybrid or large diameter rigid lenses may help decrease the amount of surface deposits ( ).

Corneal Lenses Following Refractive Surgery

Radial Keratotomy

Following RK, the cornea may exhibit significant corneal flattening with only minimal mid-peripheral flattening (approximately 0.1–0.2 mm flatter than its preoperative curvature). Therefore in the fitting of a corneal lens, a BOZR should be selected to align with the ‘more normal’ mid- peripheral cornea, approximately 4.0 mm from the centre along the horizontal meridian.

The radius of the postoperative mid-peripheral cornea can be determined through corneal mapping. Alternatively, a diagnostic lens can be selected with a BOZR that is 0.1–0.2 mm flatter than the preoperative flat K-reading and the fit can be evaluated. The appropriate BOZR should result in a fluorescein pattern that displays apical clearance over the flatter central cornea and a zone of mid-peripheral bearing at the 3 and 9 o’clock locations ( Fig. 29.16 ). The lens should display unobstructed movement along the vertical meridian.

Fig. 29.16

Fluorescein pattern postradial keratotomy. The cornea has a central flat K of 8.76 mm and a mid-peripheral curvature (4 mm temporal) of 7.94 mm. The lens has a back optic zone radius of 7.94 mm.

Lens decentration is a common problem following RK. It is often the result of uneven wound healing, which creates geographic surface elevations on which the lens pivots ( Fig. 29.17 ). Lens decentration is best resolved by increasing the overall lens diameter to 10.5 mm or larger or by moving to a scleral lens design. Final lens power is best determined by performing a sphero-cylinder refraction over a well-centred diagnostic lens.

Fig. 29.17

Pivot point created by uneven wound apposition, seen here at the top right corner of the tissue section (cat eye).

Photorefractive Keratectomy, Laser-Assisted In Situ Keratomileusis and Laser Epithelial Keratomileusis

With both PRK and LASIK, corneal lens fitting is best delayed until approximately 8–12 weeks after surgery. At this point, the refraction and topography have stabilized. At 3 months postsurgery, the integrity of the flap interface is usually sufficient to withstand the minor trauma associated with lens insertion and removal, as well as normal on-eye movements that occurs with blinking.

Many patients who have undergone PRK or LASIK can be successfully fitted with traditional spherical or aspheric corneal lenses. However, suggest that patients fitted with corneal lenses can display mild to moderate lens instability and decentration after PRK. As with soft lens fitting, the extent of tissue removal will influence the ease of fitting. For example, a patient with a preoperative refractive error of −4.00 D might end up postoperatively −1.00 D undercorrected. The 3.00-D myopic reduction was produced by an ablation of approximately 36 μm of tissue (less than the thickness of the human epithelium). The minimal difference between the central and mid-peripheral cornea creates few fitting and/or optical problems for a traditional corneal lens design. These individuals are often best fitted with a BOZR designed to align the mid-peripheral corneal topography 4.0 mm from the centre of the cornea ( Fig. 29.18 ).

Fig. 29.18

Simulated fluorescein pattern of a postlaser-assisted in situ keratomileusis eye with a −3.00 D correction.

In contrast, the corneal shape following hyperopic laser correction is steeper, with a positive value for eccentricity often exceeding 0.5–0.7 ( ). It may be necessary to consider a lens design usually reserved for keratoconus.

Reverse-Geometry Corneal Lens Designs

PRK, LASIK and LASEK are all tissue subtraction procedures and the amount of corneal tissue removed will play an important role in the postsurgical management of the patient.

Tissue removal is determined by the Munnerlyn formula:

<SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='Depthofablation=(opticzonediameter)2×(refractiveerror)/3′>Depthofablation=((opticzonediameter)2×(refractiveerror))/3Depthofablation=(opticzonediameter)2×(refractiveerror)/3

Example of myopia correction for a refractive error of −6.00 D and performing an optical zone diameter of 6.00 mm:

<SPAN role=presentation tabIndex=0 id=MathJax-Element-2-Frame class=MathJax style="POSITION: relative" data-mathml='Depthofablation=6.002×6.00/3′>Depthofablation=(6.002×(6.00))/3Depthofablation=6.002×6.00/3

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Aug 6, 2023 | Posted by in OPHTHALMOLOGY | Comments Off on Post-surgery

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