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

Peripheral vision plays a vital role in everyday tasks and overall well-being, but conventional methods of assessing visual health, such as visual acuity, focus primarily on the central vision. Visual field tests are capable of gauging peripheral vision, yet they necessitate prolonged concentration and exact fixation, which can prove difficult for individuals experiencing significant vision impairment.

Functional MRI (fMRI) with population receptive field (pRF) mapping provides a non-invasive means of mapping scotomas; however, it necessitates single contrast levels and accurate fixation. Our research team devised an fMRI-based procedure to gauge contrast sensitivity throughout the visual field without depending on precise fixation.

By integrating wide-field stimulation with varying spatial frequencies and contrast levels, and either employing pRF mapping or a structure-based retinotopic atlas, we modeled contrast sensitivity in the primary visual cortex (V1) across an extensive 40-degree segment of the visual field. In a sample of seven individuals with normal vision, we delineated the variations in V1 sensitivity across eccentricities and visual quadrants, uncovering consistent and reproducible patterns both within individuals and across sessions.

To evaluate the robustness of our approach against variations in fixation, we examined how alterations in eye movement impacted V1 sensitivity patterns in two participants. Despite the presence of eye movements, cortical sensitivity patterns remained largely unchanged, particularly at low spatial frequencies. This indicates that our approach can accommodate a range of fixation instability, rendering it appropriate for populations with unstable or biased fixation, such as individuals with dense central scotomas or strabismus.

Furthermore, our method successfully visualized simulated and disease-associated sensitivity losses at the cortical level. Notably, these findings could largely be reinstated using the structure-based retinotopic atlas, thereby eliminating the requirement for pRF mapping and precise fixation, albeit with diminished sensitivity. This integration of large-field stimulation with a retinotopic atlas presents a promising tool for monitoring vision loss and recovery across a spectrum of visual impairments, addressing a critical challenge in contemporary clinical assessments.