Visual acuity evaluated by pattern-reversal visual-evoked potential is affected by check size/visual angle.

objectiveTo systemically explore the range of visual angles that affect visual acuity, and to establish the relationship between the P1 component (peak latency ~100 ms) of the pattern-reversal visual-evoked potential (PRVEP) and the visual acuity at particular visual angles.

methodsTwo hundred and ten volunteers were divided into seven groups, according to visual acuity as assessed by the standard logarithmic visual acuity chart (SLD-ii). For each group, the PRVEP components were elicited in response to visual angle presentations at 8°, 4°, 2°, 1°/60', 30', 15', and 7.5', in the whiteblack chess-board reversal mode with a contrast level of 100% at a frequency of 2 Hz. Visual stimuli were presented monocularly, and 200 presentations were averaged for each block of trials. The early and stable component P1 was recorded at the mid-line of the occipital region (oz) and analyzed with SPSS 13.00.

results(1) oz had the maximum P1 amplitude; there was no significant difference between genders or for interocular comparison in normal controls and subjects with optic myopia. (2) The P1 latency decreased slowly below 30', then increased rapidly. The P1 amplitude initially increased with check size, and was maximal at ~1° and ~30'. (3) The P1 latency in the group with visual acuity ≤0.2 was significantly different at 8°, 15' and 7.5', while the amplitude differed at all visual angles, compared with the group with normal vision. Differences in P1 for the groups with 0.5 and 0.6 acuity were only present at visual angles <1°. (4) Regression analysis showed that the P1 latency and amplitude were associated with visual acuity over the full range of visual angles. There was a moderate correlation at visual angles <30'. Regression equations were calculated for the P1 components and visual acuity, based on visual angle.

conclusion(1) Visual angle should be taken into consideration when exploring the function of the visual pathway, especially visual acuity. A visual angle ~60' might be appropriate when using PRVEP components to evaluate poor vision and to identify malingerers. (2) increased P1 amplitude and decreased P1 latency were associated with increasing visual acuity, and the P1 components displayed a linear correlation with visual acuity, especially in the range of optimal visual angles. Visual acuity can be deduced from P1 based on visual angle.