Abstract
Purpose :
The visual system's ability to identify patterns across various spatial scales is considered a result of the retinotopic scale-invariant organization of the early visual cortex. Individuals with amblyopia, however, experience deficits in spatial vision, potentially linked to larger receptive field (RF) sizes. The relation between RF size and spatial frequency preferences in individuals with amblyopia remains unclear. To address this gap, we employed model-based fMRI to comprehensively map how the retinotopic organization in the early visual cortex may contribute to spatial deficits observed in amblyopia.
Methods :
We compared population receptive field (pRF) and population spatial frequency tuning (pSFT) estimates in early visual cortex (V1–V3) in four individuals with amblyopia and eight normally-sighted control participants. Monocular voxel-wise pRF and pSFT estimates were acquired in separate scanning sessions while eye position was monitored. We then compared pRF and pSFT estimates between eyes (amblyopic/non-dominant vs fellow/dominant eye) and between subject groups (amblyopia vs control). To further evaluate retinotopic organization, we computed a Scale Invariance metric, taking a ratio of preferred spatial frequency over pRF size (cycles/RF).
Results :
Standard models of the visual system assume that scale Invariance (cycles/RF) is constant across the visual field. However, our findings in typically-sighted participants contradict this expectation, revealing an increase in cycles/RF at the innermost eccentricities. This departure from scale invariance is also observed in the fellow eye of individuals with amblyopia, but not in the amblyopic eye. Instead, our data suggests that the amblyopic eye not only exhibits larger RF sizes but also fewer cycles/RF in central vision. While a comparison of Scale Invariance metrics reveals no significant difference across groups (P > 0.01), a marked reduction in cycles/RF is observed in the amblyopic eye compared to the fellow eye (P < 0.01).
Conclusions :
The amblyopic eye showed fewer cycles/RF in central vision compared to the fellow eye and normally-sighted controls, consistent with deficits in the sampling of spatial frequency information in amblyopia. Together, our data suggest that differences in both RF size and spatial frequency tuning contribute to visual deficits observed in individuals with amblyopia.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.