Cornea Transplantation:
The New Era of Endothelial Keratoplasty

Corneal transplantation has evolved rapidly over the past decade, as surgeons strive to refine selective tissue transplantation to treat diseases that affect specific layers of the cornea.

The first successful penetrating corneal transplantation was performed by Eduard Zirm in 1905. In 1931, Ramon Castroviejo, M.D., while a fellow at Mayo Clinic, refined the techniques for penetrating keratoplasty (PK) familiar to cornea surgeons today.

Although PK has been more popular than lamellar keratoplasty traditionally, the techniques for lamellar keratoplasty have advanced dramatically. At present, posterior lamellar (endothelial) keratoplasty is the treatment of choice for corneal endothelial disease, and deep anterior lamellar keratoplasty is strongly advocated for corneal stromal disease.

The majority of corneal transplantations at Mayo Clinic are performed for patients with Fuchs endothelial dystrophy. "Our experience with Descemet stripping endothelial keratoplasty, or DSEK, for these patients has developed favorably over the past six years," notes Sanjay V. Patel, M.D., of the Department of Ophthalmology at Mayo Clinic in Rochester, Minn. "We have been fortunate to examine many of the patients receiving DSEK in our prospective evaluation of DSEK outcomes study, with three years of follow-up for many of the participants."

Visual outcomes gain importance

Graft survival has been the traditional measure of success in corneal transplantation. The long-term survival of DSEK grafts, however, will be determined only with long-term follow-up. The risk of early endothelial failure (either primary or iatrogenic) is higher with DSEK than with PK. This outcome is explained by the high rate of endothelial cell loss caused by the surgical manipulation of the donor tissue (23 percent cell loss from preoperative at one month postoperative).

Penetrating keratoplasty (PK)

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Images of Descemet stripping endothelium keratoplasty (DSEK)

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Despite the high initial rate of endothelial cell loss, the rate of subsequent cell loss rapidly diminishes, with 26 percent loss from preoperative at six months and 39 percent loss at two years. This rate is in contrast to the higher rate of cell loss after PK, and it confirms the results of other published series. The reason for the low rate of central endothelial cell loss after one month is unknown, but it may relate to anatomical differences between DSEK and PK.

Because of promising intermediate-term endothelial cell loss rates and graft survival, visual characteristics are likely to become a more important measure of success in the future.

Traditionally, visual outcomes have been difficult to interpret because of confounding factors and the variable ability to provide the best refraction for eyes with high refractive errors and irregular astigmatism after PK. Endothelial keratoplasty results in good uncorrected visual acuity with predictable postoperative refractive errors and low astigmatism. As a result, measurement of visual outcomes will become easier and more standardized.

Postoperative visual acuity outcomes

The main visual advantage of DSEK over PK is the ability to provide a predictable postoperative spherical equivalent with little, if any, induced cylinder. For many patients, this outcome results in good uncorrected visual acuity (20/50, Snellen equivalent, in our study at two years).

Because visual acuity varies less after endothelial keratoplasty than after PK, it is likely to become a more important determinant of success in endothelial keratoplasty. "We assessed multiple aspects of vision after DSEK in our prospective study, in which patients with other causes of decreased vision have been excluded," says Dr. Patel. Outcomes include the following:

• At two years, one-third of the participants have 20/20 visual acuity or better. Mean best corrected visual acuity is 20/28. Better postoperative visual acuity is associated with better preoperative acuity and younger age.
• Many patients do not achieve 20/20 acuity after DSEK. However, they do note subjective improvement in their quality of vision. Graft thickness does not affect visual acuity. Other factors have yet to be determined.
• In pseudophakic eyes after DSEK, the center and the peripheral domains of the retinal image point-spread function are degraded compared with otherwise healthy pseudophakic eyes of similar age. This outcome implies that eyes after DSEK have considerably more high-order aberrations and intraocular forward scatter (disability glare) than do healthy, pseudophakic eyes.
• Results also indicate that scattered light originates and persists from the subepithelial region of the host cornea, whereas interface scatter diminishes over the first two years after surgery.

The exact contributions of all of these variables to postoperative vision have not been fully elucidated. Nevertheless, it is becoming apparent that chronic changes in the retained host cornea affect the optical properties of eyes after DSEK.

The field of endothelial keratoplasty continues to evolve. "Descemet membrane endothelial keratoplasty (DMEK) is on the horizon," says Dr. Patel. "The success and adoption of DMEK will depend on whether it can provide better graft survival or vision than DSEK. Although initial reports suggest improved visual outcomes with DMEK, this result will be confirmed only through standardized vision assessment in a randomized controlled trial. Our observational study after DSEK continues in a follow-up phase, and we expect it will provide longer term outcomes of the procedure."