Rapid, objective detection of cataract-induced blur using a bull's eye photodetector

Purpose: To determine whether optical aberrations caused by cataract can be detected and quantified objectively using a newly described focus detection system (FDS). Setting: The Wilmer Opthalmological Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA. Methods: The FDS uses a bull's eye photodetector to measure the double-pass blur produced from a point source of light. To determine the range and level of focus, signals are measured with a series of trial lenses in the light path selected to span the point of best focus to generate focus curves. The best corrected visual acuity (BCVA), refractive error, lens photograph grades, and FDS signals were obtained in 18 patients scheduled to have cataract surgery. The tests were repeated 6 weeks after surgery. Results: The mean FDS outcome measures improved after cataract surgery, with increased peak height (P = .001) and decreased peak width (P = .001). Improvement in signal strength (integral of signal within ±1.5 diopters of the point of best focus) strongly correlated with improvement in peak height (R² =. 88, P<.0001) and photographic cataract grade (R² = .72, P<.0001). The mean BCVA improved from 20/50 to 20/26 (P<.0001). The improvement in BCVA correlated more closely with FDS signal strength (R² = .44, P = .001) than with cataract grade (R² = .25, P = .06). Conclusions: Improvement in FDS outcome measures correlated with cataract severity and improvement in visual acuity. This objective approach may be useful in long-term studies of cataract progression.