Gung-mei Chao

10-Hz flash visual evoked potentials predict post-cataract extraction visual acuity.

Cataract patients suspected of having disease which might interfere with good postoperative visual function were referred for evaluation. Monocular steady-state luminance visual evoked potentials (VEPs) were elicited with closed eyes at a stimulus rate of 10 flashes/sec. VEPs were rated as either normal or abnormal. Patients with normal VEPs were predicted to have an acuity of 6/15 (20/50) or better. Patients with abnormal VEPs were predicted to have acuities of 6/18 (20/60) or worse. Postoperative acuities were determined for all patients who underwent surgery and who had no intraoperative or early postoperative complications. The association of preoperative VEPs and observed postoperative acuities were quantitatively compared by a 2 × 2 contingency table for the 59 eyes which met these criteria. The chi-square was significant (p < 0.001). The overall accuracy of prediction was 76%. Accuracy was 80% for patients with a preoperative acuity of 6/60 (20/200) or better and 75% for those whose postoperative acuity was 6/120 (20/400) or worse. This difference was not statistically significant.

Acuity estimated by visually evoked potentials is affected by scaling

Seven subjects whose corrected Snellen acuities were normal had their monocular acuities (14 eyes) tested by visually evoked potentials (VEPs) elicited by eight checkerboard patterns which reversed 15 times per second. Check size ranged from 20 to 3.4 min arc. Monocular VEP acuities were determined by least squares regression with linear or logarithmic scales of amplitude and pattern size. Pattern size was measured as arc minutes (horizontal size) or fundamental spatial frequency of the checkerboard. The extrapolated VEP acuities were obtained by analyses of variance and post hoc tests. The presence of statistically significant differences in VEP acuity which result from varying combinations of stimulus and response scales indicates a need for caution in selecting scales for VEP estimates of visual acuity.

Preoperative prediction of postoperative visual acuity in patients with cataracts: A quantitative review

Many tests of visual function have been proposed as means of preoperatively evaluating cataract patients surgical outcomes. It is impractical to compare all of these tests simultaneously on the same group of patients. Quantitative reviews apply quantitative methods to comparisons across studies. We compared the results of 52 reports in which cataract patients postoperative acuity was predicted by means of visually evoked potential, laser interferometry, or projection tests (potential acuity meters-pinhole). The results of each study were summarized in a 2 × 2 contingency table. Summary statistics were compared by means of analysis of variance and post hoc tests. Despite difficulties in metaanalysis, we found the visually evoked potential a better predictor with dense opacities. We recommend standardization in a quest for more precise predictions of postoperative visual acuity.

Comparison of preoperative 10-Hz visual evoked potentials to contrast sensitivity and visual acuity after cataract extraction

Cataract patients whose surgical outcomes were in question were referred for testing by visual evoked potentials, elicited through closed eyelids by a luminance stimulus (flash) that appeared 10 times per second. Visual evoked potentials were rated as normal (predicted acuity of 20/50 or better) or abnormal (predicted acuity of 20/60 or worse). Postoperative Arden and Optronix contrast sensitivities and visual acuities were determined in 37 patients who had no intraoperative or early postoperative complications. Arden grating scores of less than 100 were rated as normal. The optimal and cutoff spatial frequency values were determined for the Optronix scores. Optimal and cutoff values of greater or equal to 1 c/deg and 12 c/deg, respectively, were rated as normal. Visual acuities were considered normal at 20/50 or better. Preoperative visual evoked potentials were quantitatively compared to the postoperative contrast sensitivities and visual acuities by 2 × 2 contingency tables. The accuracy of prediction was 79% for the visual acuities, 62% for the Optronix optimal values, 70% for the Optronix cutoff values and 62% for the Arden gratings.

Symmetrical refractive error elevates stereo thresholds

We measured the effects of symmetrical spectacle blur on stereo thresholds using anaglyphlc dynamic random element stereograms (ADRES) across a two octave range of hypercyclopean spatial frequencies in three subjects. Symmetrical blur elevated subjects stereo thresholds. The absolute and relative amount of threshold elevation increased with hypercyclopean spatial frequency.

A stereo illusion induced by binocularly presented gratings: Effects of number of eyes stimulated, spatial frequency, orientation, field size, and viewing distance

We report that the binocular presentation of gratings under appropriate conditions results in an illusion of depth. Multiple levels of depth are seen simultaneously, distinguishing the illusion from the wallpaper illusion. The levels are not overlapping but are 180° out of phase relative to one another. The conditions under which the illusion is visible and under which it disappears are presented. Probable causal mechanisms, the correspondence problem, the horopter, and differential image projections of large tangential stimuli are discussed.

Binocular luminance Interaction of stereo abnormals: Visually evoked potentials

Previously, binocular Interaction was studied by using dlchoptlcally presented uniform fields whose luminance was modulated sinusoidally with a frequency of 2 Hz to elicit VEPs from stereo normal subjects. The first harmonic amplitude of VEPs decreased as Interocular phase difference (IPD) Increased from 0° to 180°, and the second harmonic amplitude has shown an asymmetrical V shaped function of IPD. The trough of the V shape was at IPD 90°, and the amplitudes at IPD = 180° were constantly smaller than at IPD = 0° at lower luminance but greater than at higher luminance. The present study attempts to determine the changes of VEPs In stereo deficient subjects with normal monocular visual acuities. We found that whether their VEPs were similar to normals or different from normals varied with (1) the diagnosis, (2) the mean luminance, and (3) the VEP component, i.e., VEP first or second harmonic.

The relationship between binocular and monocular visually evoked potentials elicited by uniform field stimulation

We elicited binocular and monocular VEPs using sinusoidally modulated uniform fields. The amplitudes and phases of the first and second harmonics were used to compare the binocular VEP to the monocular VEPs and their vector sum. We found that 1) binocular VEP first and second harmonic phases are more stable as contrast increases than monocular VEP phases, 2) the binocular VEP first and second harmonic amplitudes are greater than those of monocular VEPs, 3) the binocular VEP first harmonic amplitude is greater than the vector sum of the left and right monocular VEPs, but 4) the binocular VEP second harmonic amplitude equals the vector sum of the monocular VEPs.

Direction of perceived motion-in-depth in ambiguous dynamic random element stereograms

We measured five subjects thresholds for both stereo detection and change in axis of perceived motion-in-depth as a function of the bar width of square-wave reversing square-wave gratings-In-depth. Stereo detection varied curvilinearly with bar width, while change in the perceived direction of motion-in-depth varied linearly with bar width on logarithmic coordinates. The changes in perceived axis of motion-in-depth could not be explained by variations with bar width in disparity thresholds suggesting that subjects perceived bars move along an axis towards the nearer of two alternative positions in 3D space.

Visually evoked potentials elicited by lateral displacement and stereo motion

VEPs were recorded as subjects viewed synchronous and asynchronous dynamic random element displays monocularly or hlnocularly through green filters or dlchoptlcally through a red filter In front of the right and a green filter In front of the left eye. Viewed through green filters the synchronous displays resulted in a percept of coherent 2D motion whlle the asynchronous displays did not. Viewed dichoptkally both displays resulted In a percept of 3D motion. VEPs differed across the different conditions In both amplitude and phase.