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DSAEK linked to posterior corneal changes that markedly reduce net corneal power
J Cat Refract Surg. 2010;36(8):1358-1364.
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Descemet's stripping automated endothelial keratoplasty significantly reduced corneal power because of an increase in posterior curvature, a study showed.
The reduction in corneal power was attributed to alteration of the posterior corneal profile, the study authors said.
"The contribution of the graft-host interface to the optical quality after DSAEK is not fully understood," they said. "However, it can be speculated that the inherent difference in refractive indices between the host and the graft, as well as changes secondary to wound healing at the interface, have some influence on the final corneal power."
The study included 32 eyes of 28 patients who underwent DSAEK. A control group comprised 32 age- and gender-matched normal eyes. The DSAEK group had a mean age of 69.7 years; the control group had a mean age of 66.2 years. All corneal measurements were made with the Pentacam rotating Scheimpflug imaging system (Oculus).
Study results showed that mean true net corneal power was 40.55 D in the DSAEK group and 42.49 D in the control group. The difference was statistically significant (P < .01). Mean posterior corneal astigmatism was 0.59 D in the DSAEK group and 0.32 D in the control group; the difference was statistically significant (P = .029).
The DSAEK group had statistically significantly lower mean equivalent K readings in all zones than the control group (P < .01).
The between-group difference in mean central corneal thickness (628 µm in the DSAEK group and 553 µm in the control group) was statistically significant (P < .01).
Further study with a larger patient population may provide more insight into changes in corneal power wrought by altered anterior and posterior corneal curvature, the authors said.
Prasher et al have presented detailed quantitative analysis of the posterior curvature that confirms the clinical tenet that DSAEK induces a total hyperopic shift of about 1 D to 1.5 D. They have confirmed that this shift is mainly a result of an increase in posterior corneal curvature due to the hour-glass shaped donor lenticule. The authors also showed a flattening of the anterior surface, which they attributed to their clear corneal incision approach, correctly recognizing that a scleral incision of even 5 mm is refractively neutral in DSAEK. However, elimination of corneal edema by itself (without an hour-glass lenticule) can also induce a hyperopic shift, as has been shown by DMEK studies published recently by Price et al. The next step in DSAEK is the control of the key factors (such as lenticule shape) that induce hyperopic shifts so that predictability of individual shifts can be even more accurate.
– Mark A. Terry, MD
Director, Corneal
Services, Devers Eye Institute, Portland, Ore.
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