14 — Optical coherence tomography reflects brain atrophy in multiple sclerosis: A four-year study

This was a really fun paper to read because it was well-written and carried a really strong narrative:

Namely, MRIs are used to help determine the progression of multiple sclerosis, but they’re expensive and time-consuming. Optical Coherence Tomography, or OCT, is a noninvasive, relatively quick eye-scan that captures a 3D image of the retina. OCT scans can deliver information about retinal thickness, retina health, etc.

This paper demonstrates that in many cases, retinal layer thickness closely covaries with detectable brain lesioning. In other words, when using an MRI to determine the progression of MS, an OCT scan may be a good substitute.

The retina is, fundamentally, a part of the brain, even though it sits in the eyeball (and not in the glob we usually consider to be “brain”). Brain lesions — dead or dying brain tissue — are thought to exist both in the grey jello of the brain as well as in the retina and/or optic nerve (the jury is still out which it is, or if it’s both). Neurons undergo “Wallerian degeneration”, or cell-level shrinking back of neurites, when they fail to synapse on target neurons (due to, perhaps, damage to the axon itself, or to the downstream neuron). This means that some ganglion cells of the retina — which only send outputs to thalamus — shrink considerably from these optic nerve lesions.

OCT is able to detect the change in retinal thickness because of this cell damage, and this in turn correlates with damage to the (harder-to-scan) brain. The authors of this paper in particular were able to show this covariance in over 100 patients, over the course of four years.

This is exciting for the field because it means that MS patients can possibly undergo fewer full-brain scans and still have valuable prognosis information. In my opinion, this also has the potential to shed light on the nature of the disease, as retina is far more accessible for study than brain matter.