Retinotopic Imaging of Retinal and Cortical Structure and Function: A New Paradigm for Assessing the Visual Connectome in Health and Disease

Abstract

Purpose : Vision loss can lead to structural and functional changes in the brain. Such changes can impose preconditions on the outcomes of sight-restoration treatments. Characterizing the fine-scale relationships between retinal pathology and neuroimaging data enables a detailed analysis of the interplay between vision loss, brain plasticity and vision restoration. Presenting brain imaging in a format familiar to ophthalmologists will help generate novel insights.

Methods : There is a one-to-one and topology-preserving mapping between points in the brain and points on the retina in each of the brain regions that are part of the central visual pathway. This retinotopic organization allows brain measurements to be displayed in the same coordinates as a fundus image. Retinotopic coordinates for cortical areas V1-V3 were determined by fitting a deformable template [1] to digital reconstruction of a patient’s cortex derived from T1w MRI data. The template-derived retinotopic coordinates in V1 were extended to the optic radiation, reconstructed from diffusion MRI data [2].

Results : We present two patients with unilateral hemifield loss, one due to a recent onset of Non-Arteritic Ischemic Optic Neuropathy (NAION) (1 month prior to imaging) and another due to maculopathy caused by trauma (9 yr prior). Subjects underwent multimodal retinal and brain imaging. Functional assessments with microperimetry and fMRI (on-off full-field flashing light) were obtained. fMRI data were displayed in fundus coordinates. There was a striking qualitative correspondence between regions of fMRI signal modulation, retinal pathology and microperimetric field size. The spatial extent of attenuated V1 response often extended beyond the visible extent of the structural retinal lesion. The patient with a longer history of visual field loss showed a robust suppressive response in the V1 lesion projection zone. Cortical thickness in V1 did not reliably correlate with visual-field loss.

Conclusions : Projecting brain-imaging data to the coordinates of a fundus image enables direct comparisons between retinal structure and function and their impact on the central visual pathways. This novel visualization of brain imaging data is intuitive to ophthalmologists, leading to insights that are otherwise not readily available.
1. Benson NC, et al, PLoS Comput. Biol. 2014
2. Kammen A, et al, NeuroImage 2016
In honor and memory of Bosco S. Tjan, without whom this work would not have been possible

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.