| Glenn - USAEyes.org 2004-12-25, 7:09 pm |
| Predicting Corneal Haze After LASEK Using an Ablation Depth/Corneal
Thickness Ratio
Investigators at the university of Texas-Houston Medical School
conducted a retrospective, comparative, interventional case series
study aimed at investigating the usefulness of ablation depth/corneal
thickness (AD/CT) ratio to predict corneal haze after laser epithelial
keratomileusis (LASEK).
Fifty patients (90 eyes; mean age of patients, 40.9 years) with
myopia, hyperopia and/or astigmatism underwent bilateral or unilateral
LASEK for correction of refractive error. After epithelial flaps were
created using an 18 percent alcohol solution, bilateral or unilateral
LASEK was performed using the Alcon Autonomous LADARVision 4000
excimer laser. Visual acuity (best spectacle-corrected and
uncorrected) and refractive error were measured before and after
LASEK. Corneas were assessed by two independent evaluators under a
slit-lamp biomicroscope with broad tangential illumination. The
relative haze scale was quantitated: 0 (clear), 0.5+ (trace), 1+
(mild), 2+ (moderate), 3+ (marked) and 4+ (severe). Mean preoperative
spherical equivalent refraction was -5.46 +/- 3.74D (range, -12.375 to
+5.00D), mean ablation depth was 93.04 +/- 45.03 microns (range, 21.2
to 207.2 microns) and mean AD/CT ratio was 0.18 +/- 0.09 (range, 0.04
to 0.41).
Of 90 eyes, 40 had a higher ablation depth (AD/CT ratio greater than
0.18) and 50 eyes had a lower ablation depth (AD/CT ratio less than
0.18); 92.5 percent of eyes in the higher ratio group developed
clinically significant haze (1+ or greater). In the lower ratio group,
94 percent of eyes developed no more than 1+ corneal haze, if any. The
authors concluded that the AD/CT ratio is useful for predicting
corneal haze after LASEK. An AD/CT ratio of 0.18 or more suggests that
patients have a high risk of developing clinically significant haze
(1+ or more) after LASEK.
SOURCE: Lin N, Yee SB, Mitra S, et al. Prediction of corneal haze
using an ablation depth/corneal thickness ratio after laser epithelial
keratomileusis. J Refract Surg 2004;20(6):797-802.
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Next up (hopefully) will be a similar formula for the ablation
depth/corneal curvature/pupil size/optical ablation size ration.
Glenn Hagele
Executive Director
Council for Refractive Surgery Quality Assurance
Email to glenn dot hagele at usaeyes dot org
http://www.USAEyes.org
http://www.ComplicatedEyes.org
I am not a doctor.
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