Purpose: Traditional visual acuity (VA) measurements depend on subjective responses, which can be unreliable, especially with uncooperative participants. Objective measurements with visual evoked potentials (VEP) address this issue but can overestimate VA in amblyopia. This study aims to establish the P300 component of the event-related potential as an objective VA test for amblyopia and compare its performance to subjective (psychophysical) and VEP-based VA estimates.
Methods: Psychophysical, VEP-based, and P300-based VA estimates were obtained for amblyopic and fellow eyes of 18 participants (aged 19-65) in a bicentric study. VEP-based VA was determined from the spatial frequency threshold derived from occipital cortex pattern-pulse responses to check-sizes ranging from 0.048° to 8.95°. P300 responses were collected using visual oddball sequences with circular optotypes. The threshold was estimated from the sigmoid function of parietal P300 amplitude versus optotype gap size. Mean VA values for amblyopic eyes were compared across methods.
Results: VEP-based VA of the amblyopic eyes overestimated psychophysical VA by 0.18 ± 0.06 logMAR (P = 0.0016). In contrast, P300-based VA showed no significant difference from psychophysical VA (0.00 ± 0.04 logMAR, P > 0.05).
Conclusions: In amblyopia, P300-based optotype VA aligns more closely with psychophysical VA than VEP-based VA, suggesting that P300-based VA is a valid objective alternative for estimating VA in amblyopic eyes.
Translational relevance: This study highlights the potential of P300-based VA testing as a reliable and objective method for assessing VA in amblyopic eyes, offering a promising tool for clinical and research applications where traditional methods fall short.