MAR 17, 2008
Selective endothelial transplantation is changing the face of corneal surgery. The rapid rehabilitation and minimal postoperative astigmatism following use of this technique have quickly brought it into the mainstream. But with the accrual of experience in this area, it has become apparent that patients undergo an initial hyperopic shift after the procedure that does not seem to be entirely explained by changes in anterior corneal curvature. Several authors have proposed that the meniscus-shaped donor lenticule has a "minus lens" effect that leads to a hyperopic refractive shift.
The current study presented a series of nine patients who experienced a mean +1.26 D change after a mean of 134 days following Descemet stripping endothelial keratoplasty (DSEK) for the treatment of corneal endothelial dystrophy or failure. Seven of the patients had Fuchs dystrophy, one pseudophakic bullous keratopathy, and one congenital hereditary endothelial dystrophy.
High-resolution anterior segment optical coherence tomography (AS-OCT) images that were taken presented the less common observation that as the patients progressed after surgery, the thickened peripheral graft edges became thinner and there was a regression towards emmetropia. The authors attributed this to the tissue reshaping and deturgescence that results in a flatter graft with less of a "minus" shape. They said that their results, in combination with other published research, suggested that surgeons should target intraocular lenses -1.00 to -1.25 D more myopic than the intended refractive outcome for combined DSEK and cataract procedures.
Another interesting point the authors made is that through the simple application of thick lens optics, moving the posterior surface of the cornea posteriorly decreases the effect of the converging power of the cornea and may account for some of the induced hyperopia. As patient expectations for minimally invasive corneal transplantation outcomes rise, surgeons will be expected to accommodate for such subtleties and maximize refractive results.