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EK with thinner grafts linked to improved BCVA

Cornea. 2011;30(4):388-391.

Issue: June 10, 2011

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Endothelial keratoplasty with thinner donor tissue yielded significantly better visual outcomes than did EK with thicker grafts, a study found.

"Our results demonstrate that thin EK results in better visual acuity," the study authors said. "This idea is further supported by current research to perfect the 'ultrathin' lamellar keratoplasty, Descemet membrane EK. ... With our data in mind, we propose that surgeons consider using thinner tissue to optimize visual results in EK."

The retrospective study included 33 eyes of 28 patients who underwent routine EK with precut eye bank tissue. Anterior segment optical coherence tomography was used to measure central graft thickness.

Median postoperative graft thickness was 131 µm. Eyes were assigned to two groups: 17 eyes with graft thickness of 131 µm or less and 16 eyes with graft thickness of more than 131 µm. The average follow-up interval was 12.8 months.

Study results showed that 94% of patients had improved visual acuity and no patients lost best corrected visual acuity. Eyes with thin grafts had significantly better BCVA than eyes with thick grafts (P < .01).

All eyes with thin grafts had BCVA of 20/25 or better; 71% of eyes had BCVA of 20/20. Fifty percent of eyes with thick grafts had BCVA of 20/25 or better, and 19% had BCVA of 20/20.

"Our excellent visual acuity results with thin EK allow one to ask how thin the posterior donor disks need to be to maximally optimize visual acuity outcomes," the authors said. "Further studies need to be done to look at the differences in both visual acuity and endothelial cell loss with thin EK versus Descemet membrane EK."

The authors performed a retrospective review of DSAEK cases and found that transplanted donor tissues thinner than 131 µm produced higher percentages of 20/20 and 20/25 results than eyes with thicker donor tissues. Importantly, they did not report a Pearson correlation analysis of tissue thickness and visual acuity, which is the appropriate statistical analysis to link a specific factor to a specific outcome. Such an analysis would have shown no relationship between tissue thickness and visual acuity.

The other major flaws of this study were the propensity for subjective selection bias, retrospective review, and a low “n.” The authors began with 92 eyes reviewed, but ended up with only 33 eyes for analysis, effectively eliminating 64% of their cohort. Selection bias is also likely the reason why their “thin” tissue group achieved 100% of eyes 20/25 or better: a result that far exceeds that of not only all other DSAEK reports, but also all reports on DMEK (the epitome of “thin” tissue surgery). Whether “thin” tissue yields superior vision can be better supported or refuted by a much larger study with appropriate correlation analysis. This study by Neff et al, while provocative, is not definitive.

– Mark A. Terry, MD
Director of Corneal Services, Devers Eye Institute, Portland, Ore.
Disclosure: Dr. Terry has no relevant financial disclosures.