[Pattern visual evoked potentials visual acuity--the evaluation of visual acuity of less than 0.1]

We previously developed a new method for estimating objective visual acuity by means of pattern visual evoked potentials (PVEP). In this study, this method was applied to the evaluation of visual acuity of 0.05 and 0.01.

Ten subjects with visual acuity of 0.05 and ten normal subjects with visual acuity of 0.01 were examined. The visual acuity of the subjects was decreased step by step by means of plus spherical lenses of increasing power. In the PVEP study, the stimulus consisted of black and white checkerboards with a visual angle of 8 degrees (central stimulus) and a global field with a 5 degrees central circular scotoma (peripheral stimulus), contrast level of 15%, and a frequency of 0.7 Hz. One hundred PVEP responses were averaged per session. We reported that there was a linear relation between log subjective visual acuity of 0.1-1.0 and log check size of the patterns with PVEP. In reference to that, the check sizes of the patterns were estimated at 66' with visual acuity of 0.05, and 107' with visual acuity of 0.01. Each visual acuity was then used with other check sizes of three patterns.

With central stimulus the P100 components of O1, O2, and Oz were recorded with 66' and 82' patterns at visual acuity of 0.05(central stimulus). The P100 components of O1, O2, and Oz were 107', 137' and 161' at visual acuity of 0.01(central stimulus). There was no P100 component at visual acuity of 0.05 and 0.01(peripheral stimulus).

This method of PVEP is a useful tool as an objective estimation of visual acuity less than 0.1 and is presumed to stimulate preferentially the X retinal ganglion cell to parvocellular pathway.