Simulating the straylight effects of cataracts

PURPOSE: To study the additional straylight falling on the retina (retinal straylight) caused by cataract and find commercially available filters to simulate the cataract straylight effects. SETTING: Research laboratory. METHODS: The retinal straylight addition of cataract was derived from straylight parameter data in the literature. The scattering characteristics of cataract-simulating filters were measured using a scatterometer. RESULTS: The straylight addition due to cataract follows a power law as a function of angle with power of -2.12 and straylight parameter log values of up to 1.6 for relatively mild cataract cases. Of the commercial filters that were tested, the Tiffen Black Pro Mist (BPM) filters resembled the straylight characteristics of cataracts fairly well. The filters had a limited effect on visual acuity and contrast sensitivity, which was also found for early cataracts. The BPM 2 followed a power law as a function of angle with power of approximately -2.21 and straylight log values of 1.12. CONCLUSIONS: The BPM 2 filter is a good early-cataract-simulating filter. Stacking such filters is a good way to increase the cataract density. A drawback is that the BPM 2 filter has a transmission of 66% so stacking filters reduces the overall transmission significantly.