Purpose: To quantify visual performance of patients with achromatopsia at various contrast and luminance combinations typical for daily living conditions, in comparison to controls, and to measure beneficial effects of short-wavelength cutoff filter glasses used by patients with achromatopsia to reduce glare sensation.
Methods: Best-corrected visual acuity (BCVA) was tested with Landolt rings using an automated device (VA-CAL test). The visual acuity space was assessed for each participant with and without filter glasses (transmission >550 nm) at 46 contrast-luminance combinations (18%-95%; 0-10,000 cd/m2). The BCVA differences between both conditions were calculated for each combination as absolute values and relative to individual standard BCVA.
Results: Fourteen achromats (mean ± SD: 37.9 ± 17.6 years) and 14 normally sighted controls (mean ± SD: 25.2 ± 2.8 years) were included in the study. Without filter glasses, achromats' BCVA was best at 30 cd/m2 (mean ± SEM: 0.76 ± 0.046 logarithm of the minimum angle of resolution [logMAR], contrast = 89%) and worst at 10,000 cd/m2 (mean ± SEM: 1.41 ± 0.08 logMAR, contrast = 18%), a deterioration up to 0.6 logMAR due to increased luminance and decreased contrast. Filter glasses improved achromats' BCVA for almost all luminances by about 0.2 logMAR but lowered controls' BCVA by about 0.1 logMAR.
Conclusions: The VA-CAL test provides numerical proof that short-wavelength cutoff filter glasses can help patients with achromatopsia in everyday life, avoiding the common situation of severe visual impairment at certain daily object contrasts and ambient luminances.
Translational relevance: The VA-CAL test discovers losses of spatial resolution in the visual acuity space not seen in standardized BCVA assessment. Filter glasses improve the patients' daily visual performance, rendering them a strongly recommended visual aid in achromatopsia.