Differential impacts of strabismic and anisometropic amblyopia on the mesoscale functional organization of the human visual cortex

We employed high-resolution fMRI to distinguish the impacts of anisometropia and strabismus amblyopia on the evoked ocular dominance (OD) response. Sixteen amblyopic participants (8 females) plus 8 individuals with normal vision (1 female), participated in this study for whom, we measured the difference between the response to stimulation of the two eyes, across areas V1-V4.In controls, the evoked OD response formed the expected striped pattern within V1. Compared to controls, the OD response in amblyopic participants formed larger fused patches that extended into downstream visual areas. Moreover, both anisometropic and strabismic participants showed elevated OD responses across V1-V4.Beyond these common effects, and despite similar densities of amblyopia between the two groups, strabismus and anisometropia had differential impacts on the OD bias, binocular response and correlation between V1 depth levels. Specifically, we found a greater increase in the size of V1 portion that responded preferentially to fellow eye stimulation in anisometropic compared to strabismic individuals. We also found a greater difference between the amplitudes of the response to binocular stimulation, in those regions that responded preferentially to the fellow vs. amblyopic eye, in anisometropic compared to strabismic participants. In contrast, strabismic participants demonstrated increased correlation between the OD responses evoked within V1 superficial and deep depths, whereas anisometropic individuals did not.These results provide the primary direct functional evidence for distinct impacts of strabismus and anisometropia on the mesoscale functional organization of the human visual system, thus extending what was inferred previously about amblyopia from animal models.Significance Statement Amblyopia is a developmental disorder caused by perturbations to normal binocular visual experience during the critical period impact. Despite its high prevalence, our current understanding of amblyopia impacts on the mesoscale functional organization of primary visual area (V1) is mostly based on invasive techniques in animals. In this study we showed the primary direct evidence for the distinct impacts of anisometropia versus strabismus (two major causes of amblyopia) on the fMRI activity evoked within the human visual cortex. Our findings also confirmed the hypothesized link between the evoked OD response and the interocular visual acuity difference in amblyopia.