FORWARD LIGHT SCATTER AT ONE MONTH AFTER PHOTOREFRACTIVE KERATECTOMY

BACKGROUND: Although it is known that backward light scatter increases transiently following most excimer laser photorefractive keratectomie s (PRKs), it is not clear that there is a significant increase in forw ard light scatter, which is of primary concern for the patient. The ob ject of this study was to determine if there is a significant change o f forward light scatter at 1 month after (PRK) with an ablation zone d iameter of 6 mm. METHODS: Overlapping subsets of 24 normal myopic eyes were tested before (on the day of surgery) and 1 month after PRK, usi ng three instruments: a Stray Light Meter (16 eyes); a Computerized St ray Light Meter (14 eyes); and a mesopic Increment Threshold-Glare Par adigm (six eyes). Differences between the two eyes before PRK were com pared with the differences between the same eye before and after PRK, using repeated measured analysis of variance. In addition, increment t hreshold data obtained from 22 eyes after PRK were compared with those of 60 controls of the same age range and distribution by a t test. RE SULTS: None of the statistical comparisons approached significance at the alpha = 0.05 level. Changes in light scatter as small as a factor of 1.95 (Stray Light Meter) and 1.55 (Increment Threshold-Glare Paradi gm) could be detected as significant with a high power (0.8). Changes larger than a factor of 21 could be detected with a power of 0.8 for t he Computerized Stray Light Meter. CONCLUSIONS: In these data, there i s no support for the hypothesis that forward light scatter increases s ignificantly 1 month after PRK with an ablation zone of 6 mm. Any incr eases in forward light scatter are unlikely to be greater than a facto r of 1.5 to 2 under daytime or nighttime illumination conditions.