The Eyes Have It

I approach my MS as a student, gathering information where I can, and I almost always learn something new at each of my appointments with the neurologist. Although I know there is a lot that I don’t know about multiple sclerosis, it always surprises me to hear something new out of what I think is routine procedures.

Evidence of optic neuritis after a relapse

This week, I was back seeing my neuro as a follow-up for my relapse. My annual MRI in early June showed no new lesions, but the radiologist saw evidence of optic neuritis (ON), for which I immediately did a five-day course of steroids. My neuro wanted to see me after the steroids had the opportunity to work and after I had my appointment to see an ophthalmologist for my annual eye exam. There are a number of things going on with my body right now and not all are related to my MS, including my changing vision, so I already had an eye exam scheduled before all of this came up.

My ophthalmology appointment

The ophthalmology appointment was lengthy and thorough, and not surprisingly it showed a decline in my vision. But this doctor also disputed that I had optic neuritis now or ever, saying he found no evidence during his exam to support the radiologist’s report and that he had no need to look at my MRI to check the facts.

I relayed to my neurologist that the eye doctor said he saw no evidence of ON during my exam, nor does he think I have ever had any damage to my vision due to MS. I made him laugh when I told him the ophthalmologist questioned why would I believe anyone but an eye doctor. I pointed out to my neuro that almost all these expert specialist doctors have egos, including him, and they hate for others to tread in their territory. To reaffirm his position that I have had ON, the neuro did my eye exam that includes flashing that darn light in my eyes, and then said I have something with a name I didn’t quite catch that shows my ON damage. ‘What was that term again? I ask.

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Afferent pupil defect

"Afferent pupil defect" was his reply, and then he went on to explain what this means in terms I understand. Our brain reacts to the input it gets from our eyes. Even though the doctors may shine that irritating light in one eye, its effect shows in both of our eyes. When one eye receives the stimulus of the light, that message is sent to our brain through the optic nerve, processed in our midbrain, and immediately sent back to both of our eyes, via the third cranial nerve.

Why doctors shine that light in our eyes

All these years I thought when they were looking at one eye, they were looking at one eye. It turns out they are really seeing the reaction in both eyes. There is a fairly simple explanation of how this works, along with a chart showing the process of light in and out of available through this academic paper How to test for a relative afferent pupillary defect (RAPD).1

The importance of eye exams with MS

Perhaps I missed class the day they explained this process of how the eye receives signals, but at least I remember the part about our pupils constricting when exposed to light and how they dilate in the darkness. My neurologist casually mentions that he has noted RAPD before on my exams and there is no doubt in his thinking that I have damage to my optic nerve, so there is a difference of opinion between these two doctors. One thing both of these doctors do agree on, though, is the eyes are the window to seeing medical problems, especially for those of us with MS. Regular and thorough exams are essential – have you had your eyes checked lately?

Wishing you well,


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