Mapping Visual Contrast Sensitivity and Vision Loss Across the Visual Field with Model-Based fMRI

Abstract 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 combined with precise fixation, often very 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 is limited by its reliance on single contrast levels and the necessity of accurate fixation. We developed an fMRI-based approach to measure contrast sensitivity across the visual field without the need for precise fixation. By combining large-field stimulation with varying spatial frequencies and contrast levels with either pRF mapping or a retinotopic atlas based on anatomical landmarks, we modeled contrast sensitivity in the primary visual cortex (V1) over a large (40 deg) expanse of the visual field. In seven normal-sighted participants, we characterized differences in V1 cortical sensitivity across eccentricities and visual quadrants, finding reliable and reproducible patterns of sensitivity differences at individual and session levels. To assess the method’s tolerance to fixation variability, we further investigated how different levels of eye movement affect cortical sensitivity patterns in two participants. We found that cortical sensitivity patterns were largely preserved across eye movement, particularly at low spatial frequencies. This suggests that 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 cases of simulated and disease-linked sensitivity loss at the cortical level. Crucially, we demonstrated that these results could be largely recovered using a structure-based retinotopic atlas, eliminating the need for pRF mapping and precise fixation - although such an approach reduced sensitivity. This approach, integrating large-field stimulation with a retinotopic atlas, offers a promising tool for monitoring vision loss and recovery in patients with various visual impairments, addressing a significant challenge in current clinical assessments. Competing Interest Statement The authors have declared no competing interest. Footnotes Funding: This work was funded by Moorfields Eye Charity PhD Studentship GR001315 (London, UK), the Birkbeck-UCL Centre for NeuroImaging (BUCNI; London, UK); and Wellcome Career Development Award (306332/Z/23/Z). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Commercial Relationships: None 1) New Data and Analyses: Added results from two participants examining the impact of eye movements on cortical contrast sensitivity, demonstrating robustness to fixation variability (Figures 7 and 8); Expanded simulated vision loss analysis to include an additional condition (upper right quadrant loss), further validating the method's sensitivity to localised cortical changes (Figure 10). 2) Methodological Improvements: Improved description of correction method for eccentricity values in the Benson atlas using the Horton & Hoyt cortical magnification model, improving alignment with empirical pRF data (Figure 3 and Appendix Figure A4); Clarified statistical reporting, and standardised the presentation of p-values and degrees of freedom; Updated descriptions of stimulus parameters, task procedures, and GLM analysis to improve reproducibility. 3) Revised Figures and Text: Added Figures 7-8 to illustrate eye movement effects and Figure 10 to illustrate new simulated scotoma condition; Updated Figure 6 to include Spearman correlation coefficients for test-retest reliability; Reorganised the Introduction to clarify the motivation and clinical potential of the fMRI-based approach, with improved references and logical flow. 4) Expanded Discussion: Addressed inter-subject variability in cortical sensitivity maps, discussing potential anatomical and functional factors; Emphasised the clinical applicability of the method, particularly for patients with unstable fixation or dense scotomas; Highlighted future directions, including validation in larger cohorts, integration with structural measures (e.g., OCT), and exploration of alternative retinotopic templates (e.g., DeepRetinotopy).