Exploring the retina as a window to the brain

There are some major neurological disorders that are difficult to diagnose and assess by MRI in their earliest stages but have certain indications that can be seen in the eye. One such condition is Multiple Sclerosis (MS). Optical Coherence Tomography, more frequently known as OCT, can be used to assess the retinal damage caused by MS, which acts as a marker for the wider neurodegenerative process that occurs inside the whole brain. Neurologist and MS expert Professor Bart Van Wijmeersch, who leads the University MS Centre in Pelt, Belgium, explains how OCT imaging can help in determining MS prognosis, treatment and follow-up. 

Multiple Sclerosis is a lifelong autoimmune condition that affects the central nervous system. At the start of the disease, some lesions are produced inside the brain, which can cause an initial symptom. This is categorised as a ‘clinically isolated syndrome’. When it repeats itself, it becomes known as ‘relapsing-remitting MS’, and later on, it can progress into other forms, such as progressive-MS. On a cellular level, MS develops through a combination of inflammatory lesions, simultaneous axonal loss (an axon is known as a ‘nerve fibre’ and carries electrical impulses from neuron to neuron) and demyelination (damage to the myelin sheath around nerves), which cause neurodegeneration and brain atrophy. However, MS can prove difficult to diagnose because it can progress below a clinical threshold for many years without the patient noticing. And while MRI can be used to detect lesions over time, it is not always 100% reliable in detecting all lesions inside the brain. “Cortical grey matter lesions, in particular, do not show up well on MRI,” explains Prof. Van Wijmeersch. “Around 80% of these lesions are not seen.”

First indications 

The optic nerve is one of the three key areas most often initially affected by 

MS, alongside the brain and spinal cord, and optical neuritis (inflammation of the optical nerve) can be one of the first indicators of the disease. OCT is used to image and measure the different layers of the human retina and can provide detail on any retinal damage caused by MS. “Around 80% of MS patients have atrophy in the retinal nerve fibre layer and ganglion cell layer of the retina, and 40% of patients have problems with the inner nuclear layers of the retina,” says Prof. Van Wijmeersch. “With OCT there is the possibility to examine these layers in detail, in real life.” 

Important assessment tool 

OCT is a fast and non-invasive way of mapping the layers of the retina and, as such, is used in many medical specialties beyond ophthalmology, such as cardiology and research. It can be used in MS assessment in three ways: diagnosis, prognosis and follow-up of treatment. “Using OCT in a diagnostic way for MS is not so surprising, because one of the first symptoms of the condition is optic neuritis, but it can also be 

used on a prognostic level, and in follow-up of treatments or follow up of these patients over time,” says Prof. Van Wijmeersch. “I think this is the most promising contribution that OCT makes in MS assessment, and I believe that it can have a very big impact in clinical practice. What happens on the retina mirrors what happens inside the brain in MS,” he continues, “studies have shown that atrophy in the brain over time due to MS correlates very much with loss of retinal nerve fibre layer thickness over time. So, the smaller that is, the more atrophy there is.” Detecting the progression of MS and neurodegeneration before the patient is affected by it can offer the possibility of treatment that can slow the loss of neurons and even restore some of the damage caused by the disease.

Tool for the future 

Predicting the progression of MS, independent of relapses, is something that remains very hard to achieve, because there has been a lack of good biomarkers for neurodegeneration, but Prof. Van Wijmeersch is hopeful. “Using OCT to map changes in the retinal nerve fibre and ganglion cell layer can help as a baseline for prognosis, in guiding your treatment choices, and also follow up on patient treatment responses in MS. I think it's a real tool for the future.” 

Alongside its reputation as a leader in MRI, CT and Ultrasound technology, Canon Medical is becoming increasingly recognised in ophthalmology for its range of high-quality eye care imaging systems. This article is kindly abstracted from Canon Medical Systems Europe VISIONS magazine #38. 

About Prof. Van Wijmeersch 

A neurologist and specialist in Multiple Sclerosis (MS), Professor Bart Van Wijmeersch is the Medical Director of the University MS centre in Pelt, Belgium, where he leads a multidisciplinary team. He is also an Associate Professor of Neurology at the University of Hasselt in Belgium, where he’s involved in pre-clinical, as well as clinical research on MS. He co-founded, and was the first president of the ParadigMS Foundation – an organisation dedicated to MS education and improving the everyday clinical care of people with MS. He is also a member of the Belgian Study Group of Multiple Sclerosis and a number of advisory boards. As an acknowledgment of his scientific work, Prof. Van Wijmeersch received an honorary award from the Flemish Government in 2019.