P300-based acuity estimation in imitated amblyopia

A frequent approach to estimating visual acuity objectively is the recording of visual evoked potentials (VEPs) to patterns of different coarseness. This, however, overestimates acuity in patients with fragmented and distorted vision such as in amblyopia. This is likely due to VEP-based techniques using checkerboard or grating stimuli. We hypothesized that no overestimation would occur when the event-related potential P300 in response to optotype stimuli is used for acuity estimation.

In 29 visually normal participants, we recorded P300 responses to Landolt C optotypes of different sizes. Vision was artificially degraded by placing a patterned polymethyl methacrylate pane in front of the monitor, which resulted in fragmentation and distortion of the stimulus. As control, a frosted pane was used. Both panes were adjusted to yield the same reduction of acuity in a standard subjective acuity test. A difference of less than 0.1 log MAR was defined as criterion to judge the outcomes of the objective tests as equivalent for both types of artificial visual impairment.

The average difference of P300-based objective acuity estimates between types of visual degradation was significantly smaller than 0.1 log MAR, indicating that the performance of the objective acuity test was equivalent for both types of visual degradation.

Our data suggest that P300-based objective acuity testing with optotype stimuli is more akin to standard psychophysical acuity testing and thus a suitable approach in cases of visual impairment where VEP-based methods fail to yield reliable results.