Hyperacuities are visual alignment discrimination judgments which yield lower thresholds than expected, given the photoreceptor density of the retina. Vernier bias is the perceptual alignment error (or subjective alignment position relative to true physical alignment) that is manifest during vernier hyperacuity testing. Few studies have been performed on vernier bias, leaving its purpose and etiology unknown. Since monocular vernier biases and the monocular components of fixation disparity are similar in magnitude and distribution, it is hypothesized in this study that non-stressed fixation disparity equals the sum of the monocular vernier biases. Twenty-six subjects were tested both with the Mentor BVAT II and with a software program developed at the Pacific University College of Optometry in order to measure fixation disparity and monocular vernier biases respectively. A two-tailed T -test and linear regression performed on the data show that under these testing conditions a significant correlation between monocular vernier biases and fixation disparity does not exist (mean difference = 23.7 arc sec, P-value < 0.1176; R-value = 0.0122, R-squared value = 0.015).
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