Objective line spread function measurements, Snellen acuity, and LOCS II classification in patients with cataract

We tested an instrument to measure the line spread function (LSF) of the eye in order to assess objectively retinal image degradation due to cataract. Optical aberrations from 62 eyes with early to moderate cataract were assessed by measuring the extent of blurring of a best-focused fine line image (LSF) projected onto a subject's retina. The instrument consisted of a slitlamp equipped with a Hruby lens to project the line and a computer-coupled CCD camera to record and measure the blurred image. We hypothesized that the width of the blurred line image (called WSCAT) due to light scattering in the cataractous lens would be affected most by nuclear and subcapsular cataracts. The WSCAT results were compared to the data from two other tests: (1) Snellen acuity and (2) LOCS II cataract classification. Grouping eyes by Snellen acuity we found that WSCAT from the group with 6/4.5 (20/15) or 6/6 (20/20) acuity was distinguishable from the group with 6/9 (20/30) or worse acuity (95% confidence interval). Data also were analyzed using a regression model which corrects for the intraclass correlation between the two eyes of an individual. Results show a significant association between WSCAT and minimum angular resolution (MAR) derived from Snellen visual acuity (regression coefficient of 5.45, p = 0.008). WSCAT also is correlated with both LOCS II nuclear opalescence (NO) and posterior subcapsular (P) categories with regression coefficients of 3.03 (p = 0.004) and 2.07 (p = 0.054), respectively. Results from measurement of LSF indicate the potential for this instrument to assess retinal image degradation associated with nuclear and posterior subcapsular cataract objectively.