Mapping human visual contrast sensitivity and vision loss across the visual field with model-based fMRI.

Peripheral vision is crucial for daily activities and quality of life, yet traditional measures of visual function like visual acuity primarily assess central vision. Visual field tests can evaluate peripheral vision but require extended focus and precise fixation, often challenging for patients with severe sight loss. Functional MRI (fMRI) with population receptive field (pRF) mapping offers a non-invasive way to map scotomas but relies on single contrast levels and accurate fixation. We developed an fMRI-based approach to measure contrast sensitivity across the visual field without requiring precise fixation. Combining large-field stimulation with varying spatial frequencies and contrast levels, and either pRF mapping or a structure-based retinotopic atlas, we modeled contrast sensitivity in the primary visual cortex (V1) over a large (40 deg) expanse of the visual field. In seven normally sighted participants, we characterized differences in V1 sensitivity across eccentricities and visual quadrants, finding reliable and reproducible patterns at individual and session levels. To test robustness to fixation variability, we investigated how varying levels of eye movement affected V1 sensitivity patterns in two participants: cortical sensitivity patterns were largely preserved despite eye movements, particularly at low spatial frequencies. This suggests our approach can accommodate several degrees of fixation instability, making it suitable for populations with unstable or biased fixation for whom visual field maps are harder to acquire behaviorally (e.g., patients with dense central scotoma or strabismus). Additionally, our method effectively visualized simulated and disease-linked sensitivity loss at the cortical level. Crucially, these results could be largely recovered using the structure-based retinotopic atlas, eliminating the need for pRF mapping and precise fixation, although with reduced sensitivity. This approach, integrating large-field stimulation with a retinotopic atlas, offers a promising tool for monitoring vision loss and recovery across a range of visual impairments, addressing a significant challenge in current clinical assessments.