R. Limbonsiong et al., SCREENING OF MYOPIC PHOTOREFRACTIVE KERATECTOMY IN EYE BANK EYES BY COMPUTERIZED VIDEOKERATOGRAPHY, Archives of ophthalmology, 116(5), 1998, pp. 617-623
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.