Binocular Imbalance in Amblyopia Depends on Spatial Frequency in Binocular Combination

Abstract

PURPOSE. To assess the role of spatial frequency on binocular imbalance in binocular combination in adults with amblyopia. METHODS. Ten amblyopes (23 ± 4.9 [SD] years old; one deprivation, two mixed, seven anisometropia patients) and 10 age-matched normal adults (23 ± 2.3 years old) participated. The interocular contrast ratio (fellow eye/amblyopic eye, i.e., the balance point [BP]) that resulted in an equal contribution of both eyes in binocular combination was measured using a binocular orientation combination task at 0.5, 1, 2, and 4 cycles per degree (c/d). The extent of binocular imbalance was quantified as the absolute value of the BP on log scale (i.e., |logBP|). RESULTS. When the base contrast of the amblyopic eye was set at 100% (Experiment 1), the |logBP| was found to be significantly affected by stimulus spatial frequency (F(1.44, 26.01) = 51.6, P < 0.001, η 2 g = 0.40) and group (F(1, 18) = 66.97, P < 0.001, η 2 g = 0.74), the interaction between spatial frequency and group was also significant (F(1.44, 26.01) = 38.12, P < 0.001, η 2 g = 0.33). Such spatial frequency-dependent binocular imbalance remained present, even when the base contrast of the amblyopic eye was set at equal suprathreshold contrast levels across spatial frequencies (Experiment 2). CONCLUSIONS. Binocular balance was more disrupted at higher spatial frequencies in binocular combination in amblyopia. This imbalance might not originate solely from the amblyopic eye's deficit in contrast sensitivity but is likely to be related to the difference in contrast sensitivity between the eyes.

A clinically convenient test to measure binocular balance across spatial frequency in amblyopia

“…Recently, Mao et al. used the orientation task to test adult amblyopes ( Mao et al., 2020 ) and confirmed the findings of previous studies ( Ding et al., 2013a , 2013b ; Kwon et al., 2015 ) that binocular imbalance peaks at a higher spatial frequency (4 c/deg).…”

Interocular Suppression as Revealed by Dichoptic Masking Is Orientation-Dependent and Imbalanced in Amblyopia

“…The degree of suppression strength in amblyopes found in this masking study at high spatial frequencies ( Supplementary Figure S3 ) is at odds with a number of previous reports. A reduced masking imbalance between the fellow eye and amblyopic eyes was previously shown at high spatial frequencies in the masking study of Zhou et al 23 However, using a different approach, one involving suprathreshold stimuli, Kwon et al, 57 Reynaud and Hess, 58 and Mao et al 59 found an increased binocular imbalance at high spatial frequency. They measured balance points using fusion/matching tasks under suprathreshold conditions (i.e., the contrasts in both eyes were well above the detection thresholds), whereas Zhou et al 23 and the present study measured suppression at detection threshold (i.e., target in tested eye was at threshold, and mask in untested eye was suprathreshold).…”

Binocular Integration of Perceptually Suppressed Visual Information in Amblyopia

“… 21 , 22 , 31 – 34 Suppression of amblyopic eye information from conscious awareness was thought to preclude its contribution during binocular viewing. Our results show that despite strong suppression using high-contrast stimuli, 23 , 24 , 33 , 91 , 92 visual information seen only by the suppressed amblyopic eye can be binocularly integrated and influence the overall visual percept. We further corroborate previous findings for the normal visual system that suppressed stimuli can be binocularly integrated.…”