Shuai Chang¹ (), Yan Yang², Shuying Liu¹, Xinping Yu¹, Ming Meng³; ¹Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China, ²Sichuan Provincial People's Hospital, School of Medicine, University of Electronic Science and Technology of China, ³University of Alabama at Birmingham

Strabismus can lead either to persistent diplopia or to chronic suppression of input from the strabismic eye, implying distinct cortical strategies for handling mismatched binocular signals. Yet it is unknown how primary visual cortex (V1) represents strabismic-eye input in these divergent outcomes. We combined task-based fMRI with multivariate pattern analysis (MVPA) to compare V1 representations in strabismic patients with diplopia, strabismic patients without diplopia, and visually normal controls. Participants viewed colored orthogonal gratings under three conditions: dominant eye alone, strabismic eye alone, and binocular stimulation. Retinotopic mapping defined an individual V1 region of interest. We analyzed univariate BOLD amplitudes and multivoxel patterns using representational similarity and decoding of eye-of-origin and viewing condition. In diplopic strabismus, V1 showed little reduction of binocular BOLD responses relative to monocular viewing, and MVPA revealed robust decoding of dominant versus strabismic eye as well as monocular versus binocular trials. Monocular and binocular patterns were less similar when the strabismic eye was stimulated, consistent with parallel, separable V1 representations of inputs from the two eyes. In non-diplopic strabismus, dominant-eye responses were relatively preserved, whereas binocular BOLD responses were suppressed and patterns elicited by strabismic-eye and binocular stimulation were poorly decodable and more similar to dominant-eye patterns, indicating loss or remapping of strabismic-eye–specific information in V1. Controls showed well-separated patterns for all conditions with high decoding accuracy. These results suggest that the presence versus absence of diplopia in strabismus is linked to distinct V1 coding regimes for strabismic-eye input: maintained, decodable eye-of-origin representations versus early suppression and restructuring before signals reach conscious awareness.