Effect of pupillary dilation on retinal nerve fiber layer thickness as measured by scanning laser polarimetry in eyes with and without cataract

Purpose: This study was conducted to evaluate the effect of pupillary dilat ion on retinal nerve fiber layer (RNFL) thickness as measured by scanning l aser polarimetry (SLP) in cataractous and noncataractous eyes. Methods: The study included 31 eyes of 31 consecutive patients (mean age, 6 2.5 +/- 14.0 years; range, 30-76 years). Eyes with refractive error exceedi ng 5.0 D sphere or 2.0 D cylinder, nonlenticular media opacity, cup-to-disc ratio >0.9, corneal disease, ocular inflammation, or previous intraocular surgery were excluded. A standard reticule was used to measure pupillary di ameter. Cataract grade was evaluated by a single observer using the Lens Op acities Classification System (LOCS III). RNFL thickness measurements were obtained by means of SLP before and after pupillary dilation. Results: Of the patients, 10 had clear lenses and 21 had variable degrees o f lenticular opacification. In four eyes, imaging could not be performed be cause of dense cataracts. Mean pupillary diameters before and after dilatio n were 2.5 +/- 0.7 mm and 7.3 +/- 1.1 mm, respectively. There were no signi ficant differences in global RNFL thickness before and after dilation in no ncataractous and cataractous eyes. Among cataractous eyes in which imaging was possible, there was no correlation between difference in RNFL thickness before and after dilation and nuclear opalescence, nuclear color, and cort ical and posterior subcapsular grading of the LOGS III score. Six of 27 eye s (22.2%) had a change of more than 10% in RNFL thickness after pupillary d ilation. Conclusion: Although pharmacologic mydriasis does not statistically alter R NFL thickness as measured by SLP, approximately one fifth of such eyes will have a change of more than 10% in retardation. Uniformity in pupil size is recommended when longitudinally evaluating RNFL measurements.