Retinotopic cortical mapping as an objective functional monitoring tool of macular therapy

Abstract

Purpose : Psychophysical measures such as best-corrected visual acuity (BCVA), reading acuity (RA), contrast sensitivity (CS) or microperimetry (MP) heavily rely on patient compliance. Here we develop an objective, user-independent method based on brain mapping using functional magnetic resonance imaging (fMRI) for monitoring macular function under therapeutic intervention.

Methods : 20 patients with neovascular age-related macular degeneration (nAMD) were studied with high-field, high-resolution fMRI, BCVA testing, RA, CS and MP before and after 3 monthly intravitreal injections of ranibizumab. Functional MRI utilised population-receptive field (pRF) mapping to provide retinotopic data that were then compared with psychophysical measures and structural imaging (optical coherence tomography, OCT). For comparison, 20 age-matched healthy controls were measured.

Results : BCVA responders (≥5 letters) showed an increase of 29% in activated brain area, while non-responders showed a decrease of 0.8%. Radial histograms allowed for visualisation of relative differences in significant voxels numbers over eccentricity. Responders showed increases in pRF centre density in foveal regions, while non-responders no such changes. Absence of intraretinal fluid and preservation of outer retinal layers was associated with higher numbers of active V1 voxels and consistently better BCVA. The association of subretinal fluid (SRF) with active V1 voxel number and BCVA was in the opposite direction indicating a superior functional outcome if SRF is present. An improved RA is associated with higher voxel numbers and shows a stronger correlation with fMRI parameters than BCVA, CS or MP.

Conclusions : Our results clearly show that fMRI is applicable in patients suffering from nAMD and offers objective assessment of treatment response and functional recovery across the visual field at the level of V1. This demonstrates the potential of retinotopic mapping for quantitative, topographic measurement of visual function independent of patient compliance. This makes fMRI-based brain mapping ideally suited for monitoring retinal gene therapy effects.

This is a 2020 ARVO Annual Meeting abstract.