SCREENING OF MYOPIC PHOTOREFRACTIVE KERATECTOMY IN EYE BANK EYES BY COMPUTERIZED VIDEOKERATOGRAPHY

Background: In contrast to incisional keratotomy, corneas that have un dergone photorefractive keratectomy may be difficult to detect by insp ection with slitlamp biomicroscopy alone. Eye bank corneas that have u ndergone high myopic refractive surgical correction could potentially result in substantial postoperative hyperopic correction if used as do nor tissue for corneal transplantation. Surface irregularities or disp lacement of the treated optical zone within the graft in relation to t he entrance pupil of the recipient could result in significant induced astigmatism and distortion. This study examines computerized videoker atographic screening of eye bank globes as a strategy for detecting my opic photorefractive keratectomy. Methods: Preoperative and postoperat ive corneal topographic maps of freshly enucleated human and rabbit ey es that have undergone myopic photorefractive keratectomy with an exci mer laser were placed in a globe-fixating device and analyzed using a vertically oriented videokeratoscope. The same system was applied in a n actual eye bank setting, and potentially transplantable globes from donors without a history of corneal surgery were analyzed. Results: Co mputerized videokeratography using a vertically mounted system reliabl y detected photorefractive keratectomy in 12 of 12 human eye bank corn eas treated by excimer photorefractive keratectomy in a range between -1.5 to -6.0 diopters. This method also detected similar changes on la sed rabbit corneas enucleated 6 weeks after excimer surgery. Data proc essed with the tangential mode yielded a ''bull's-eye'' topography pat tern reflecting central corneal flattening that was more sensitive in detecting myopic corrections than the conventional axial formula-based color maps. False-positive results were not detected in 96 cadaver gl obes sequentially screened in the eye bank. Conclusions: Computerized videokeratography represents a feasible method to screen donor globes for myopic photorefractive keratectomy as shown by the in vitro and ra bbit models. However, only whole globes and not corneoscleral sections are amenable to processing with this technique. Tangential maps provi ded greater sensitivity in detecting low myopic corrections than the a xial formula-based color maps.