Ultra-high field functional MRI based population receptive field mapping of retinal dystrophies

Abstract

Purpose : Population receptive field (pRF) mapping methods allows mapping visual field losses due to retinal pathology, as recently shown in a study on retinal scotoma sizes at 3T. MRI scanners operating at ultra-high magnetic field (7 Tesla and above) offer increased sensitivity and specificity of brain activation maps, but also pose additional challenges in image acquisition and subject handling, particularly in clinical populations.

Methods : Ten eyes from 10 patients clinically and genetically diagnosed with Stargardt disease (STGD) (age: 29 ± 9.7; 4 female) were included in the study. Data was acquired on a 7 Tesla MAGNETOM scanner using a 32-channel head coil with 1mm isotropic resolution using the CMRR multi-band EPI sequence. Visual stimulus consisted of a moving, flickering bar covering the central 14° visual angle. In addition, patients were examined using optical coherence tomography (OCT, Heidelberg Spectralis) and microperimetry (MP-3, Nidek). Data was analyzed using mrVista to obtain retinotopic maps. Visual field coverage based on above-threshold voxels from the pRF-analysis allows for a direct comparison with retinal sensitivity maps as measured by MP.

Results : Four patients were excluded due to attention deficits or excessive movement during the MRI measurements. All remaining patients had framewise displacement (FD) values of 0.025±0.004 mm and 5068±2162 V1 voxel activated (mean±stddev). Figures show MP and pRF results of two exemplary patients with macular scotoma confined to the central 2° visual angle. It can clearly be seen that uncovered areas on the coverage maps obtained by ultra-high-field fMRI resemble areas with functional loss in MP.

Conclusions : This is the first demonstration of ultra-high field pRF mapping in patients with STGD. Coverage maps obtained from pRF data provide information complementary to conventional ophthalmic examination and allow for objective assessment of retinal dysfunction.

This is a 2021 ARVO Annual Meeting abstract.