Direct objective quantification of corneal haze after excimer laser photorefractive keratectomy for high myopia.
OBJECTIVE
The purpose of the study is to measure regional distribution differences in corneal haze after excimer laser photorefractive keratectomy for high myopia.


METHODS
The authors developed computerized gradient edge detectors with which were analyzed digitized anterior slit-lamp photographs of 40 eyes, an average of 21.0 plus or minus 14.5 weeks after photorefractive keratectomy for high myopia (-6 to -22 diopters). A treated area an adjacent untreated area on the anterior corneal surface, each containing six regions, were quantified, and the difference was correlated with various parameters.


RESULTS
Mean differences between scarred and clear areas for haze grade 0.5, 1.0, 2.0, 3.0, and 4.0 were 16.9, 26.6, 42.6, 60.4, and 76.4 gray levels, respectively (rs = 0.96; P = 0.0001). A low but statistically significant correlation between the intended correction and postoperative corneal haze was found (r = 0.33; P = 0.037). The mean coefficient of variation of the amount of opacification within each treated area was 9.4%. This coefficient of variation increased with a longer follow-up time (r = 0.88; P = 0.0001). The difference in the intensity of haze between the center and more peripheral regions over the entrance pupil did not correlate with the attempted correction. However, a strong association between a relatively less severe central corneal haze with respect to more peripheral haze and longer follow-up time was found (r = -0.96; P = 0.0001).


CONCLUSIONS
The amount of corneal haze showed a weak positive association with the attempted correction in excimer laser photorefractive keratectomy for high myopia. Corneal haze appeared fairly uniformly distributed within the ablation zone, but a more heterogeneous distribution was found with a longer follow-up time. Furthermore, later postoperative examinations disclosed a clear trend toward diminishing central opacification relative to peripheral regions over the entrance pupil.
Maldonado
M J
MJ
Department of Ophthalmology, La Fe University Hospital, Valencia, Spain.
Arnau
V
V
Navea
A
A
Martínez-Costa
R
R
Mico
F M
FM
Cisneros
A L
AL
Menezo
J L
JL
D000328:Adult; D003315:Cornea / Q000503:physiopathology / Q000601:surgery*; D003318:Corneal Opacity / Q000209:etiology / Q000473:pathology* / Q000503:physiopathology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D054018:Lasers, Excimer; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D018903:Photorefractive Keratectomy / Q000009:adverse effects*