Today’s episode is about optical coherence tomography, or OCT. It is a quick, non-invasive eye scan that allows doctors to look closely at the retina and the optic nerve. Researchers are investigating whether OCT may become an important biomarker for monitoring disease activity, treatment effects, and long-term progression in multiple sclerosis. The examination itself only takes a few minutes, but its potential may be much bigger.
To explore that, I’m speaking with Dr. Joachim Havla, neurologist and senior physician at the Institute of Clinical Neuroimmunology at Ludwig Maximilian University in Munich.
Note: This article is the English adaptation of a German interview from the MS-Perspektive podcast from May 2023.
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Introduction to Dr. Joachim Havla
Could you briefly introduce yourself?
Dr. Joachim Havla:
Of course. First of all, it’s great to be here.
My name is Joachim Havla. I’m a neurologist and senior physician at the Institute of Clinical Neuroimmunology at LMU Munich.
In my daily work I treat people with neurological diseases, especially multiple sclerosis, and I’m also involved in research.
Outside the hospital, I enjoy spending time with my family. We have three children, and we love being outdoors. Living in Munich makes that easy – we often go to the mountains or to one of the nearby lakes.
I like snow very much. What I don’t like quite as much is sand on the beach. It tends to end up everywhere in our camper van..
Nele Handwerker:
That sounds like the perfect place to live then – mountains and lakes nearby.
Dr. Joachim Havla:
Exactly. No sand involved.
Why the optic nerve is so important in MS
Let’s begin with the basics behind OCT. What is so special about the optic nerve, and why is it often described as an extension of the brain?
Dr. Joachim Havla:
The optic nerve is fascinating. If you reduce it to the simplest image, it is like a cable. It carries information from the retina, so from the back of the eye, to the brain, where that information is processed.
But it is more than just a cable. From a developmental point of view, the retina is actually part of the brain. During embryonic development, it grows out from the brain toward the front. That is why the retina has a layered structure that resembles brain tissue. And that is exactly what makes it so interesting for neurologists: we cannot simply look into the brain, because the skull is in the way. But we can look at the retina. And if we can examine the retina with a tool like OCT, then in a way we are getting a glimpse into the brain.
What the optic nerve does
What exactly is the job of the optic nerve, and what happens when inflammation affects it?
Dr. Joachim Havla:
Light enters the eye and reaches the retina. There, it is first detected by specialized cells, the rods and cones. The signal is then converted into an electrical signal and passed on through several layers of retinal nerve cells. One particularly important group are the ganglion cells. Their fibers form what we call the optic nerve. So the optic nerve is not really one single structure in the usual sense. It is the bundle of many individual nerve fibers carrying visual information to the visual cortex in the brain.
If inflammation occurs along this pathway, the signal can no longer be transmitted properly. That can lead to visual symptoms such as blurred vision, a grey veil, parts of the visual field missing, or pain when moving the eye.
How well can the optic nerve recover?
What kind of regenerative capacity do the retina and the optic nerve have?
Dr. Joachim Havla:
Because they are part of the central nervous system, regeneration is limited. It is not like the skin, where a scratch often heals quite well.
We have to distinguish between different kinds of damage. If the myelin sheath, the insulating layer around the nerve fiber, is damaged, there is at least some potential for remyelination, meaning that the myelin can be rebuilt to a certain extent. Oligodendrocytes, the cells responsible for producing myelin, can contribute to that if the inflammation has been brought under control. Axons can also sprout again to a degree, although very slowly.
What is much more difficult is the replacement of actual nerve cells. If ganglion cells in the retina are lost, the body has a hard time restoring them. That is where regeneration is very limited.
Optic neuritis in MS, NMOSD, and MOGAD
Nele Handwerker:
That also shows why it is so important to contact a doctor quickly if there are visual problems. I’d also like to widen the perspective a little.
What role does optic neuritis play in multiple sclerosis, but also in NMOSD and MOGAD? These two conditions are less familiar to many listeners.
Dr. Joachim Havla:
Yes, this can definitely be confusing, because the field has become more differentiated over time. Inflammatory optic neuritis is a common symptom in several inflammatory diseases of the central nervous system. For a long time, optic neuritis was often considered mainly in the context of multiple sclerosis. But over time it became clear that not every optic neuritis ends up being MS.
Today we know that MS, NMOSD, and MOGAD are different diseases. They do not just represent variants of the same condition. Their underlying mechanisms are different.
With MOGAD, there is a detectable antibody against myelin oligodendrocyte glycoprotein, usually called MOG-IgG. In NMOSD, many patients have antibodies against aquaporin-4, a water channel associated with astrocytes, which are support cells in the central nervous system. These biological mechanisms are different from what we see in MS.
Clinically, however, all three conditions can involve optic neuritis. That is why the diagnostic distinction is so important. In MS, optic neuritis is typically one-sided, often comes with blurred vision, reduced color vision, a grey haze, and pain with eye movement, and it usually responds well to corticosteroids. In NMOSD and MOGAD, optic neuritis is more often bilateral and can be more severe, especially in NMOSD, where the risk of major vision loss is higher and more aggressive treatment may be needed early on. MRI patterns can also differ between these conditions.
So when someone presents with optic neuritis, our job is not only to confirm the inflammation, but also to identify the cause as precisely as possible.
The bridge to OCT
Nele Handwerker:
That was a very helpful overview. And now we can come to the part that is at the center of today’s conversation: optical coherence tomography.
How did researchers discover that structures connected to the optic nerve can become thinner in people with MS even without a classic relapse, and that this could become an interesting marker for hidden disease activity?
Dr. Joachim Havla:
The starting point was that OCT gives us a way to look at retinal layers very precisely. If someone has had optic neuritis, we can clearly measure damage there. We can detect the loss of axons, and by analyzing the retinal layers we can also infer neuronal injury.
Once researchers began doing that systematically, it also became clear that the retina is not completely stable over time, even beyond acute attacks. In healthy people, brain volume gradually decreases with age, and the same is true for other tissues. In multiple sclerosis, because the nervous system is under chronic stress, loss of tissue can be greater than in healthy aging. That is why OCT became so interesting: perhaps it could help us capture some of these ongoing processes in a practical and sensitive way.
How OCT Works
Nele Handwerker:
Many listeners may have already had an OCT examination at the ophthalmologist. But not everyone knows what actually happens during the scan.
Could you explain how OCT works?
Dr. Joachim Havla:
Of course.
Optical Coherence Tomography is essentially an imaging technique that uses light waves. The device sends harmless light into the eye and measures how that light is reflected back from the different layers of the retina.
Because each retinal layer reflects light slightly differently, the device can reconstruct a very detailed cross-section image of the retina.
The result is something that looks almost like a microscopic slice through the tissue. And from that image we can measure the thickness of the different retinal layers very precisely.
In fact, the resolution is extremely high – we are talking about measurements in the micrometer range.
That level of precision makes OCT very useful for research.
Why the Retina Is Ideal for Long-Term Observation
Nele Handwerker:
So it’s almost like a tiny window into the nervous system.
Dr. Joachim Havla:
Exactly.
And there is another advantage.
The retina has a very unique pattern of blood vessels. This pattern acts almost like a fingerprint. It allows the device to identify the exact same location again during follow-up examinations.
That means we can measure the same retinal spot months or even years later and compare it directly with earlier scans.
This makes OCT particularly suitable for longitudinal studies, meaning studies that observe changes over time.
What OCT Can Show in MS
What exactly do researchers measure in people with multiple sclerosis?
Dr. Joachim Havla:
One of the most important measurements is the thickness of the retinal nerve fiber layer.
This layer contains the axons of the ganglion cells. As we discussed earlier, these axons form the optic nerve.
If these nerve fibers are damaged or lost, the layer becomes thinner. And OCT allows us to measure that thinning very precisely.
Researchers have found that after an episode of optic neuritis, the retinal nerve fiber layer often becomes thinner because some of those nerve fibers have been damaged.
But interestingly, we also see gradual thinning in some patients even without a recent optic neuritis.
That observation raised an important question:
Could this thinning reflect more general neurodegeneration in MS?
Neurodegeneration and Silent Disease Activity
Nele Handwerker:
In the podcast I often talk about neurodegeneration as a process that begins quite early in multiple sclerosis.
Relapses are the most visible events, but there can also be changes in the nervous system that happen more slowly in the background.
Dr. Joachim Havla:
That’s exactly the idea.
In multiple sclerosis we know that inflammation and degeneration can occur simultaneously. Even if a patient does not experience a clinical relapse, there can still be ongoing processes in the central nervous system.
MRI can capture some of these changes, but OCT might offer an additional way to observe them.
That is why many researchers are interested in whether retinal thinning could serve as a biomarker for these long-term processes.
What Current Studies Show
What have studies found so far? Are there clear links between OCT findings and other indicators of disease progression?
Dr. Joachim Havla:
There are several interesting observations.
Some studies have shown correlations between retinal thinning and:
• higher disability scores
• greater brain atrophy on MRI
• or more pronounced disease progression
Disability in MS is often measured using the EDSS, the Expanded Disability Status Scale.
When researchers compare OCT measurements with EDSS scores, they sometimes see that patients with thinner retinal layers also have higher disability scores.
But it’s important to emphasize that these are statistical associations.
A correlation does not necessarily mean that one factor directly causes the other.
Why Larger Studies Are Needed
Nele Handwerker:
So we need more data before we can draw firm conclusions.
Dr. Joachim Havla:
Exactly.
Many of the existing studies are relatively small. To really understand the relationship between retinal changes and disease progression, we need large cohorts of patients and long observation periods.
Another challenge is that retinal thickness is influenced by several factors, including age and other health conditions.
So when we analyze OCT data, we always have to consider these additional variables.
Looking Beyond MS
Is OCT also being studied in other neurological diseases?
Dr. Joachim Havla:
Yes, very much so.
For example, we also use OCT in research on genetic metabolic disorders in children.
These are conditions where specific metabolic pathways do not function properly. Because the diseases are genetically defined, they offer a good opportunity to observe how certain neurological processes develop over time.
OCT can help us monitor whether the nervous system remains stable or whether structural changes appear.
This shows that OCT could become relevant not only for multiple sclerosis but also for many other neurological diseases.
OCT Compared with MRI
Nele Handwerker:
One thing I personally find very appealing about OCT is how simple the examination is.
I actually had one recently. You sit down, look into the device for a few seconds, maybe follow a small fixation point — and that’s it.
Compared with that, an MRI scan can be quite demanding for some patients.
Dr. Joachim Havla:
Yes, that’s definitely true.
MRI is an extremely powerful diagnostic tool, and it remains essential in the diagnosis and monitoring of multiple sclerosis.
But it is also more complex. It takes longer, it is more expensive, and some patients find the procedure uncomfortable.
OCT, on the other hand, is very quick. The scan usually takes only a few minutes. It is painless, non-invasive, and does not involve radiation.
That makes it potentially very suitable for frequent follow-up examinations.
However, OCT and MRI do not replace each other. Rather, they provide different kinds of information.
MRI allows us to see inflammatory lesions and structural changes in the brain and spinal cord. OCT focuses on the retina and therefore gives us a very specific view of neuronal structures connected to the optic nerve.
So ideally, the two methods complement each other.
Can OCT Also Show Inflammation?
Nele Handwerker:
When we talk about OCT in MS, the focus is often on neurodegeneration — meaning the loss of nerve tissue.
But researchers are also looking at whether OCT might reveal signs of inflammation.
What exactly are scientists studying in that context?
Dr. Joachim Havla:
Researchers are analyzing different retinal layers to see whether they respond differently depending on disease activity.
One layer that has received particular attention is the inner nuclear layer, often abbreviated as INL.
This layer contains several types of nerve cells that play a role in processing visual information within the retina.
Some studies have observed that the thickness of the INL may change depending on inflammatory activity in the disease.
The Inner Nuclear Layer (INL)
What kind of changes have been observed?
Dr. Joachim Havla:
In some studies, researchers noticed that patients with stable disease tended to show a reduction in INL thickness over time.
In contrast, in patients with ongoing inflammatory activity, the INL sometimes remained thicker than expected.
This led to the hypothesis that changes in this layer might reflect inflammatory processes.
But again, we have to interpret these results carefully.
Most of these observations come from group analyses. That means researchers compare averages across many patients.
Applying these findings to individual predictions for a single patient is much more complicated.
From Group Data to Individual Prognosis
Nele Handwerker:
So the challenge is translating group-level findings into something that helps individual patients.
Dr. Joachim Havla:
Exactly.
In research we often identify patterns that are visible when we analyze large numbers of patients.
But medicine ultimately happens at the level of the individual person sitting in front of us.
One of the big goals of current research is therefore to determine whether OCT measurements could help us better predict the disease course for individual patients.
That would be extremely valuable — but we are not quite there yet.
What Needs to Happen Before OCT Becomes Routine
Do you think OCT will become part of routine MS care in the future?
Dr. Joachim Havla:
I believe it has strong potential.
However, several conditions must be met before it can be widely implemented in clinical practice.
First, clinics need to have the equipment available.
Second, trained personnel must perform the scans correctly.
And third, specialists must be able to interpret the results reliably.
At the moment, many centers perform OCT mainly in the context of research studies.
But if future research confirms its clinical value, it could certainly become a regular component of MS monitoring.
Looking Ahead
Nele Handwerker:
That would certainly be exciting, especially because the examination itself is so quick and patient-friendly.
Dr. Joachim Havla:
Yes, and the eye offers a unique opportunity.
Because the retina is part of the central nervous system, examining it may give us insights into processes that are otherwise difficult to observe directly.
That is why OCT has attracted so much attention in neurological research.
Closing
Nele Handwerker:
Dr. Havla, thank you very much for explaining OCT and its potential so clearly.
It’s fascinating how much information the eye can reveal about what is happening in the brain.
Dr. Joachim Havla:
Thank you for the invitation. It was a pleasure.
And if you’re interested in learning more about the research behind OCT and the visual system in neurological diseases, you can also explore the work of Dr. Havla’s research group here:
The lab is part of the Institute of Clinical Neuroimmunology at LMU Munich and focuses on understanding how the visual system can help us study diseases like multiple sclerosis.
See you soon and try to make the best out of your life,
Nele
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