Towards a more realistic visual performance assessment: The Tuebingen Visual Acuity Test at different Levels of Contrast and Ambient Luminance (VA-CAL)

Abstract

Purpose : Currently, visual acuity (VA) assessment is performed with maximum optotype contrast at moderately low luminance (80-320 cd/m²), barely reflecting visual environments in daily life. Specifically, VA may not adequately assess vision in inherited retinal disorders with increased glare-sensitivity like achromatopsia (ACHM). For a more realistic assessment of patients’ visual performance at different contrasts (C) and ambient luminance (AL), approximating daily life conditions, we developed a novel VA test, VA-CAL. Here we present preliminary results in ACHM patients and healthy controls.

Methods : ACHM patients (N=8; age: 16-37, mean 24.9 y) and eye-healthy controls (N=10; age: 22-29, mean 25.5 y) underwent VA-CAL. Landolt C-rings (LCR) were presented at 1m distance on a 10x10 cm field in the center of a frosted glass screen (130x130 cm), back-lit by 3,060 computer-controlled LEDs (0-10,000 cd/m², 7 steps). LCR contrast was programmable between 10-90 %. VA threshold for each condition was determined by adjusting LCR sizes using the QUEST adaptive staircase method. Participants received auditory feedback after reporting the gap position of LCR (8AFC), presented max. 10 s (ISI 1 s).

Results : As expected, VA of ACHM was well below to controls. In both, VA decreased with lower C. While VA of controls increased with AL up to a maximum between 3,000-5,000 cd/m² (max. VA mean ± SEM: -0.5 ± 0.03 logMAR @ C=90 %, AL=3,000 cd/m²), ACHM reached their max. VA at 30 cd/m² (max. VA mean ± SEM: 0.76 ± 0.046 logMAR @ C=80 %). With increasing AL, VA in ACHM decreased by about 0.08 logMAR per 1,000 cd/m² up to AL 3,000 cd/m², followed by quite steady low VA up to AL 8,000 cd/m² and a subsequent drop of VA to a minimum at AL 10,000 cd/m² (min. VA mean ± SEM: 1.41 ± 0.08 logMAR @ C=10 %) (Fig. 1).

Conclusions : In this study, a novel computer-controlled method for testing of VA under different conditions of contrast and ambient luminance was developed for a more realistic visual performance assessment of visually impaired patients. Whereas in healthy subjects VA improves initially with increasing levels of AL, in patients with achromatopsia, VA decreases with increasing C and AL. Our results indicate that VA has to be measured within a broader range of C and AL to adequately assess everyday visual performance, especially in patients reporting glare sensitivity.

This is a 2021 ARVO Annual Meeting abstract.