Visualizing the Limits of Low Vision in Detecting Natural Image Features

Purpose. The purpose of our study was to develop a tool to visualize the limitations posed by visual impairments in detecting small and low-contrast elements in natural images. This visualization tool incorporates existing models of several aspects of visual perception, such as the band-limited contrast model of Peli (J Opt Soc Am A 1996;13:1131-8). Methods. The models underlying the visualization tool were elaborated and tested in experiments with human subjects with various visual impairments such as macular degeneration, diabetic retinopathy, glaucoma and subjects with normal vision but under various degraded viewing conditions (including reduced contrast, eccentric viewing). The experiments were designed to determine in three successive steps the contrast sensitivity function that produces a degraded image that can just be discriminated from its original. In the first step, the just detectable blur was determined, while in the next two steps contrast threshold levels were determined for removing high and medium spatial frequencies from the image. Threshold parameters were determined for three image-types (face, stairs, forest) and the relationship with acuity and contrast thresholds (of Landolt-C symbols) was examined. Results. The blur threshold is inversely related to acuity, and this relationship is largely independent of the cause of reduced acuity (visual impairment, contrast reduction or eccentric viewing). Conclusions. We developed a validated visualization tool based on these results that provides a reliable impression of detectability of image features by visual impaired peopl