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Geunyoung Yoon, Cherlyn Joan Ng, Duje Tadin, Randolph Blake, Martin S Banks; Phase perception altered by long-term neural adaptation to habitual optics reduces neural binocular summation. Invest. Ophthalmol. Vis. Sci. 2019;60(9):606.
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© ARVO (1962-2015); The Authors (2016-present)
Prolonged exposure to ocular aberrations can alter perceived contrast and phase. We investigated adaptation to dissimilar optical aberrations between the two eyes to learn how adaptation affects binocular contrast summation.
Two keratoconus and three normal subjects participated in our study. A binocular adaptive optics vision simulator was used to fully correct subjects’ optical aberrations and to conduct psychophysical tests. Subjects’ monocular phase perception was quantified by presenting suprathreshold horizontal compound gratings consisting of a fundamental frequency (2 cpd) and second harmonic (4 cpd) in which relative phase shifts were manipulated. Contrast thresholds were measured monocularly and binocularly. Neural (i.e., aberration-free) binocular summation was then expressed as the ratio of the average monocular-to-binocular thresholds. The difference in monocular phase perception between the two eyes was then correlated with the binocular summation.
The keratoconus subjects had significantly different (p=0.02) perceived monocular phase angle deviations (+4.15 ± 7.20 deg) compared to the normal optics subjects (-8.25 ± 3.40 deg). Both monocular and binocular contrast thresholds were higher in keratoconus subjects compared to normal subjects with a monocular mean of 0.0238 and 0.0187, respectively (p=0.07), and a binocular mean of 0.0148 and 0.0098, respectively (p=0.08). For both subject groups, binocular summation index values ranged from 1.4 to 2, while the perceived monocular difference in phase angles ranged from 1.7 to 11.8 deg. A negative correlation was found between the perceived difference in phases between the eyes and binocular benefit at both spatial frequencies (R2 = 0.55 (2 cpd) and R2=0.52 (4 cpd)).
Long-term neural adaptation to habitual ocular aberrations alters phase perception. Differences in monocularly perceived phases in the two eyes reduced binocular contrast summation when the optical aberrations were fully corrected. These findings indicate that neural adaptation to dissimilar optics between the eyes compensates for optically induced phase deviations. However, this compensation does not contribute to summation when those aberrations are corrected.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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