Impact of Amblyopia on the Function of Stereo- and Motion-Selective Clusters in Human Extrastriate Cortex

Abstract

Purpose : Amblyopia is a developmental disorder caused by disruption of symmetric binocular visual input early in life. Most amblyopic individuals suffer from impairments in stereopsis and motion perception, especially in the central visual field. We studied the impact of amblyopia on the functional organization of fine-scale stereo- and motion-selective clusters across human extrastriate visual cortex.

Methods : We localized stereo- and motion-selective clusters across areas V2, V3, V3A and MT in 5 amblyopic (3 strabismic and 2 anisometropic) subjects and 14 controls using high-resolution (1 mm isotropic) fMRI in a 7T scanner. In separate scan sessions, we also measured speed, direction, and coherence sensitivity of the response in the motion-selective clusters. We also localized color-selective clusters in the same subjects as an internal control.

Results : Controls (≈50 arc sec randot stereoacuity) showed stereo-selective clusters across extrastriate visual areas (Fig. 1A), while amblyopic individuals (>250 arc sec) showed no significant stereo-selective response (Fig. 1B). Nevertheless, interdigitated clusters of motion- and color-selective responses were still found in areas V2/V3 of amblyopic individuals, as detected in controls. In both groups we also detected motion-selective responses within areas V3A and MT.
Despite the overall similarity in the distribution of motion-selective clusters between the two groups, the level of motion-selective response, especially to higher speeds and lower coherency levels, was weaker in amblyopic compared to control subjects. In V2 and V3, this between-groups difference: (i) was confined to those regions that represented the central (0°-3°) visual field and (ii) accompanied a weaker direction-selectivity in amblyopic compared to control subjects.

Conclusions : Amblyopia affects the functional organization and the response selectivity of stereo- and motion-selective clusters across human extrastriate visual cortex. The spatial distribution of this effect is consistent with behavioral reports of a stronger amblyopia impact on central compared to peripheral vision.

This is a 2021 ARVO Annual Meeting abstract.

 

Figure 1) Organization of motion- (red), stereo- (green) and color- (blue) selective clusters across the visual cortex of two individuals with normal (A) and amblyopic (B) vision. Borders of visual areas are indicated with black dashed lines.