Finding Multiple Sclerosis During Your Eye Exam

1) Unilateral Vision Loss

The most commonly associated ocular finding with MS is sudden onset vision loss due to optic neuritis (an inflammation of the optic nerve).  The amount of vision loss can vary, but typically ranges from 20/60 to 20/200 in the involved eye.  The typical patient population are females age 20-30, but males can be affected as well.  A hallmark is associated pain with eye movement in the eye with vision loss due to the swelling of the nerve behind the eye.  In the majority of presentations, there will be no visible swelling or edema at the optic nerve during the eye exam -- most cases are retrobulbar optic neuritis meaning the swelling is happening behind the eye.  The presenting symptoms will guide your optometrist to make the correct referral for MRI to find this swelling behind the eye, and perhaps other white matter lesions in the brain that can indicate a diagnosis of MS.

Optic Nerve Edema (swelling at the optic nerve) is a hallmark of optic neuritis.  Unfortunately, MS is more commonly associated with retrobulbar optic neuritis, meaning that the eye will look perfectly normal during your eye exam.

2) Decreased Light Sensitivity or Color Vision in 1 Eye

Optic neuritis can cause more than just vision loss.  The optic nerve delivers all visual information from the eye to the brain, so swelling along the nerve can disrupt all visual transmission.  Colors out of the affected eye may look washed out or less saturated.  Lights may look dimmer.  Your optometrist may perform some comparison tests to try to categorize this difference by looking for differences in color and brightness perception between the two eyes.  The "Red Cap" test where your doctor has you grade the degree of redness that you see between the two eyes is a common in-office measurement.

This is a great artistic rendition of an abnormal red cap test result.  The normal eye on the right has better color saturation of the red eye drop cap than the eye on the left in this case.  Via

3) Visual Field Defects

Running a visual field test on the eye with optic neuritis can show areas of significant change.  Most commonly the affected eye will show central visual field loss -- either a central scotoma (area of field loss) or a generalized depressed response of the central 30 degrees of vision.

4) Decreased Eye Muscle Movement Ability or Double Vision

Sudden onset double vision is another symptom that needs immediate investigation.  The most commonly associated defect with MS is called INO or internuclear ophthalmoplegia.  To put in layman's terms: the affected eye can't turn in towards the nose.  This means when one eye moves to turn out, the other eye is pointing straight ahead because it can't move to turn in.  As a result of this misalignment, you will see double vision (would cause horizontal diplopia, or two images side by side).  Other common eye muscle anomalies during MS include nystagmus, where the eye makes jerky back and forth movements.

Recovery:

The good news is that most patients will recover from vision loss when optic neuritis is the culprit over a period of 6-12 months.  85% of patients return to 20/40 vision or better.  Despite visual recovery over time, light and color sensitivity may remain abnormal out of the affected eye indefinitely.  There is a very strong association between an optic neuritis event and later onset of MS: 75% of women with optic neuritis will go on to develop MS over the next 15 years, and 40% of males.  

If you have sudden vision loss, it is always best to call your eye doctor immediately to schedule an examination.  Unfortunately, vision loss in one eye (especially if it is subtle) can often go unnoticed because we keep both eyes open most of the time, and hardly ever compare the two.  This is one reason why regular eye exams are so important; even if you feel your vision is great.  Finding your glasses prescription is one of the least important components of an eye exam -- the health of your eyes is really a window that your doctor uses to assess the health of the entire rest of your body!

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