Visual Performance of People With Albinism Assessed With Generalizable and Adaptive AIM and FInD Methods

Validation of Angular Indication Measurement (AIM) Stereoacuity

Background

Stereopsis is a critical visual function, however clinical stereotests are time-consuming, coarse in resolution, suffer low test-retest repeatability, and poor agreement with other tests. We developed AIM Stereoacuity to address these limitations and asked whether it could deliver reliable, efficient, and precise stereo-thresholds across stimulus types and disparity signs.

Methods

Observers reported the orientation of 5×1.25° bar defined by disparity of random dots embedded in a 6° diameter circular cell, presented in a 4*4 grid. Bar disparity was scaled from ± 2σ relative to a threshold and slope-estimate, initially set by the experimenter and adaptively updated. Orientation report errors (indicated vs. actual bar-orientation) were fit with a cumulative Gaussian function to derive stereo-thresholds. Twenty-one normally-sighted observers were tested with red-blue anaglyphs in crossed and uncrossed disparity signs across 4 element-types (8.5arcmin broadband dots, or band-pass difference of Gaussians with peak Spatial-Frequency (SF) of 2, 4, or 6 c/°). We analyzed stereoacuities, test durations, and the test-retest repeatability.

Results

Across SFs and observers, test duration for a chart were 36 and 40 secs for measuring crossed and uncrossed disparity, respectively. There was no effect of disparity sign or SF (Kruskal-Wallis; p>0.05). Median log stereo-thresholds averaged across all SFs were 1.90 and 1.84 log arcsec for crossed and uncrossed disparities, respectively. Crossed and uncrossed disparities were moderately correlated across SFs(r=0.44 to 0.79; median=0.54). Test-retest biases were 0.01 arcsec (p=0.45) and 0.10 arcsec (p= 0.001) for crossed and uncrossed disparities, respectively.

Conclusions

The results for the response-adaptive, self-administered AIM Stereoacuity method showed no significant stereo-thresholds differences between broad- and narrow-band stimuli. The test delivers repeatable results for crossed disparity in approximately 80 seconds.

Novel color vision assessment tool: AIM Color Detection and Discrimination

Color vision assessment is essential in clinical practice, yet different tests exhibit distinct strengths and limitations. Here we apply a psychophysical paradigm, Angular Indication Measurement (AIM) for color detection and discrimination. AIM is designed to address some of the shortcomings of existing tests, such as prolonged testing time, limited accuracy and sensitivity, and the necessity for clinician oversight. AIM presents adaptively generated charts, each a N×M (here 4×4) grid of stimuli, and participants are instructed to indicate either the orientation of the gap in a cone-isolating Landolt C optotype or the orientation of the edge between two colors in an equiluminant color space. The contrasts or color differences of the stimuli are adaptively selected for each chart based on performance of prior AIM charts. In a group of 23 color-normal and 15 people with color vision deficiency (CVD), we validate AIM color against Hardy-Rand-Rittler (HRR), Farnsworth-Munsell 100 hue test (FM100), and anomaloscope color matching diagnosis and use machine learning techniques to classify the type and severity of CVD. The results show that AIM has classification accuracies comparable to that of the anomaloscope, and while HRR and FM100 are less accurate than AIM and an anomaloscope, HRR is very rapid. We conclude that AIM is a computer-based, self-administered, response-adaptive and rapid tool with high test-retest repeatability that has the potential to be suitable for both clinical and research applications.