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Postkeratoplasty Contact Lens Fitting
Patients who require contact lens fitting following keratoplasty (corneal graft) can be the greatest challenge to a contact lens practitioner. These patients have undergone a major surgical procedure and may be reluctant to revert to or start contact lens wear. The practitioner needs to consider both the practical challenges of fitting the postkeratoplasty cornea and the patient's thoughts and attitude concerning contact lens wear.
History of Keratoplasty
Keratoplasty has advanced significantly since its conception in 1886 by Von Hippel (1887). , Magitot (1912), Elschnig (1930), Filatov (1935) and Castroviejo (1949,1950) were pioneers who contributed to the development of techniques for penetrating keratoplasty (PK) that became widely used from the 1940s. Deep anterior lamellar keratoplasty (DALK) was introduced in the 1980s (Archila 1983, Malbran, 1972), but technical difficulty prevented its use until 2002, when ) described a technique to bare Descemet's membrane by injecting air into the cornea to detach the membrane before carrying out an anterior lamellar keratectomy. This technique was faster, safer and easier to perform than previous methods. Since then, subsequent improvements in surgical techniques have been developed which prevent perforation and ensure better separation of the stromal tissue (Fournié 2007, ).
In 2004, Melles described a technique for sutureless Descemet's stripping automated endothelial keratoplasty (DSAEK) allowing for transplantation of posterior stroma, Descemet's membrane and endothelium (Melles 2004). In 2006, Melles described the Descemet membrane endothelial keratoplasty (DMEK) technique, enhancing the DSAEK procedure (Melles 2006). The differences between transplant procedures is shown diagrammatically in Fig. 22.1 and with an OCT scan in Fig. 22.2 .
These advances have resulted in a shift in the type of transplant procedure undertaken. The Australian Corneal Graft Registry (ACGR; ) shows a 50% reduction in penetrating keratoplasty over the past 10 years, while DSAEK and DALK have increased ( Fig. 22.3 ). also reported this trend in the UK. It is important to understand the different surgical techniques as these will influence postkeratoplasty corneal thickness, morphology, sensitivity and topography.
While surgical techniques have been evolving, there has also been a steady increase in the variety of contact lenses available. This, in conjunction with preservative-free steroids, has allowed for earlier postgraft contact lens fitting.
Indications for Keratoplasty
Advances in surgical techniques have resulted in changes in graft indications ( Table 22.1 ). Fig. 22.4 breaks down the indications per graft type, PK, DALK and EK (ACGR Report 2015).
Table 22.1
Keratoplasty Techniques – Indications and Selection (From Tan, D.T., Dart, J.K., Holland, E.J. and Kinoshita, S., 2012. Corneal transplantation. The Lancet 379, 1749–1761.)
| PK | Selective LK | Ocular surface reconstruction | Boston type 1 keratoprosthesis | |||
|---|---|---|---|---|---|---|
| ALK | EK | Limbal epithelial transplantation | Cultivated mucosal epithelial transplantation | |||
| Effect of transplant on the host cornea and requirements for donor preparation | Replaces all five corneal layers (figure 1) | Replaces only the epithelium and stroma with donor Bowman's membrane and stroma; DALK decribes the removal of almost all the host stroma | Replaces only Descemet's membrane and the endothelium (removed by stripping) with donor endothelium and Decemet's membrane, with or without stromal carrier | Replaces only the epithelial layer with donor tissue which includes donor limbus (stroma and epithelium) | Replaces the epithelial layer with ex-vivo cultivated epithelium (usually on a carrier of amniotic membrane) | Replaces all five layers by a Perspex optical device fixated within a conventional allogeneic donor PK |
| Variations in technique | The donor may be cut manually or with a mechanical trephine or with a femtosecond laser known as FLAK * | Two variations in DALK technique are used: pre-Descemetic DALK † and Descemetic DALK ‡ | Two principal variations in technique are used: Descemet's stripping EKS and Descemet's membrane EK ¶ | The donor limbus can be a conjunctival limbal autograft; allografts can be from living related donors (lr-CLAL) or from a cadaveric donor (KLAL) | The donor epithelium can be of limbal origin (CLET) or mucosal origin (COMET) | Replaces only the epithelial layer; with donor tissue often with amniotic membrane transplantation as adjunctive treatment |
| Indications for corneal transplantation and for technique selection | ||||||
| Ocular surface disorders ‖ | NA | NA | NA | Yes | Yes | NA |
| Corneal ectasias ** | Yes | Yes | NA | NA | NA | Not as a primary procedure |
| Primary and acquired stromal disorders †† | Yes | Yes (unless the scarring is full thickness) | NA | Combined with PK or DALK when there is limbal stem cell, deficiency (eg, after chemical burns or in aniridia) | Combined with PK or DALK when there is limbal stem cell deficiency (eg, after chemical burns or in aniridia) | In some cases of aniridia and chemical injuries |
| Endothelial disorders ‡‡ | Yes | NA | Yes | NA | NA | Not as a primary procedure |
| Late endothelial failure ʃʃ | Yes | NA | Yes | NA | NA | Yes if associated with recurrent transplant rejection episodes |
| Immunological disorders ¶¶ | Yes (when central and associated with corneal perforation) | Yes | NA | NA | NA | NA |
| Therapeutic (usually carried out to treat infection) | Yes | Yes in some cases | NA | NA | NA | NA |
None of these procedures are effective in severely dry eyes. PK = penetrating keratoplasty. LK = lamellar keratoplasty. ALK = anterior lamellar keratoplasty. EK = endothelial keratoplasty. DALK = deep anterior lamellar keratoplasty. FLAK = femtosecond laser- assisted keratoplasty. lrCLAL = living related conjunctival limbal allograft. KLAL = cadaver-donor keratolimbal allograft. CLET = cultivated limbal epithelial transplantation. COMET = cultivated oral mucosal epithelial transplantation. NA = not appropriate. Femtosecond laser-assisted keratoplasty. In pre-Descemetic DALK, more than 75% of the stroma is removed; in descemetic DALK, all the stroma is removed. In Descemet's stripping EK, a manually prepared (Descemet's stripping endothelial keratoplasty) or machine cut (Descemet's stripping automated endothelial keratoplasty) posterior corneal layer is transplanted. In Descemet's membrane EK, the donor Descemet's membrane and endothelium is used without the stroma using Descemet's membrane endothelial keratoplasty, when the donor is prepared manually, or Descemet's membrane automated endothelial keratoplasty, when the donor is prepared with the aid of a microkeratome. Ocular surface disorders: such as chemical burns, severe inflammatory disease (eg, in some cases of ocular pemphigoid and Stevens Johnson Syndrome), and congenital disorders (eg, aniridia). Corneal ectasias: commonly keratoconus, post-lasik corneal ectasia, keratoglobus, and pellucid marginal degeneration. Primary and acquired stromal disorders: corneal stromal dystrophies (eg, lattice, granular and macular), post-infectious scars (after herpes simplex virus, bacterial fungal, and Acanthamoeba keratitis), post-traumatic scars. Endothelial disorders: commonly Fuch's corneal dystrophy, pseudophakic and aphakic bullous keratopathy. Late endothelial failure: follows acute or recurrent transplant rejection episodes or endothelial cell loss unrelated to rejection. Immunological disorders: commonly associated with rheumatoid arthritis and Mooren's ulcer.
Instead of PK, anterior stromal disease, including keratoconus, is now mostly treated with DALK, whereas endothelial disease is treated with DSAEK or DMEK. Fig. 22.5 shows the survival rates for graft surgical procedures over 30 years. The reader will note that survival rates are lower for newer techniques compared with traditional PK. Studies suggest that earlier DALK techniques caused early graft failures and complications ( , ), but more recent developments have greatly improved graft survival and visual outcomes, and there is less endothelial cell loss compared with PK. analysed graft survival and showed that patients who had undergone DALK showed a graft survival of 97.2 ± 2.0% compared with 73.0 ± 2.0%, 5 years after surgery. They also showed a marked difference in the predicted graft survival indices. DALK survival was predicted to be 63.2 ± 6.0% at 20 years and 10.5 ± 4.0% at 40 years, whereas PK predicted graft survival was calculated as 23.9 ± 2.0% at 20 years and 1.2 ± 0.4% at 40 years.
Despite the change in indications for keratoplasty, the intended benefit remains the same. The ACGR (2015) reports improving visual function is the primary intended benefit of corneal graft surgery for all graft types ( Fig. 22.6 ).
The Postkeratoplasty Cornea
Corneal thickness
Multiple studies have noted a large interpatient and intrapatient variability in corneal thickness following PK and DALK. showed that in a group of 231 PK eyes, average central corneal thickness (CCT) was 540 ± 60 µm with a range of 420–740 µm measured 2 months postoperatively. showed corneal thickness following PK after a follow-up of 22 years was 608 ± 75 µm. showed in a retrospective evaluation of 236 DALK procedures between 2000 and 2006 that the average central corneal thickness after surgery was 584 ± 49 µm. The observed changes relate to corneal swelling at the time of surgery, followed by reduction in thickness due to topical steroid use. Essentially, the corneal thickness is likely to be thicker than a typical cornea following PKs and DALK; therefore pachymetry should be measured and noted in view of possible endothelial changes.
Corneal epithelium
showed the corneal epithelium in 1003 eyes had a re-epithelialisation time of 4.6 ± 13.2 days after surgery. Complete corneal epithelial healing was obtained in 1 day in 28.5% of patients, in 3 days in 65.8%, in 7 days in 93.6%, and in 14 days in 97.0%, with postoperative chronic epithelial defects occurring in 3.0% of eyes.
Endothelial morphology
Endothelial cell loss occurs at the time of surgery with traditional PK. Typically this occurs at the donor host junction, causing endothelial cells to migrate from the central cornea to the periphery. showed endothelial cell density, 10–17 years postoperatively, was 695 ± 113.6 cells/mm 2 in corneas transplanted for keratoconus. showed that the majority of endothelial cell loss occurred within the first 2 years after transplantation, approximately 48% cell loss within 2 years, and the same eyes only showing a 63% cell loss after 20 years. showed that endothelial rejection and late endothelial decompensation accounted for 50.51% of failures after 3 years.
Fig. 22.7 shows the rapid drop of endothelial cell numbers by almost two-thirds in a patient after PK over a 3-year period. Although this may not directly result in corneal oedema, the post-PK cornea may be more prone to hypoxic stress, and prolonged contact lens wear may exacerbate the decline in corneal function.
There is significantly less endothelial cell loss with DALK as the patient's own endothelium is left intact. Endothelial keratoplasties were originally shown to have a slightly reduced endothelial cell density. showed the percentage of endothelial cell loss was lower in DSAEK compared with PK at 1 year (30% ± 22% vs 37% ± 25%; p = 0.045), 2 years (36% ± 23% vs 45% ± 33%; p = 0.018) and 3 years (39% ± 24% vs 47% ± 28%; p = 0.022) postoperatively. Newer surgical techniques that preserve the donor corneal endothelium have helped to reduce this cell loss to 15% in the first year ( ).
When undertaking contact lens fitting, it is important, therefore, to ascertain which type of surgery has been undertaken and consider the potential for corneal oedema and hypoxic stress induced by a contact lens. It is worth measuring a baseline CCT and endothelial cell density prior to contact lens fitting. A high-DK material should be used in post-PK fitting, especially during the first few years.
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