Internuclear ophthalmoplegia (INO) is an eye movement disorder that impacts the ability to look to the side with both eyes at the same time. INO develops when the cranial nerve fibers that work together to pivot both eyes horizontally become damaged. It can affect one or both eyes. Patients with INO can still move the eyes up and down, but not inward. If only one eye is affected, that eye will stare straight ahead when the other eye is turned to the side, causing that eye to flutter involuntarily. This causes blurry or double vision for most people, though the severity varies.
The two main causes of internuclear ophthalmoplegia are:
- Multiple sclerosis (mostly in young people, usually both eyes are affected)
- Stroke (mostly in older people, usually only one eye is affected)
However, in rarer cases, the condition can be caused by:
- Head trauma
- Lyme disease
- Other infections
- Bilateral, where both eyes are impacted
- Unilateral, which only affects one eye
- Wall-eyed bilateral INO (WEBINO), a rare disorder that causes both eyes to turn out
- Inability to move the impacted eye toward the nose
- Blurry vision
- Double vision, typically with one image on top of the other
- Involuntary eye fluttering or blinking
- Skew deviation (a vertical misalignment of eyes)
- Some INO is caused by medical conditions, such as multiple sclerosis, lupus, Guillain-Barré syndrome or brain tumors, so it can’t be prevented.
- About one-third of all INO cases are the result of an infarction, such as a stroke. To reduce the risk of a stroke, follow a healthy diet and exercise regularly.
- Behcet’s disease
- Brain tumors
- Guillain-Barré syndrome
- Lyme disease
- Trauma to the head
- Medical examination. A physical examination is often enough to diagnose internuclear ophthalmoplegia.
- Imaging studies. Some patients will need an MRI or a CT scan to locate damage and help diagnose the underlying cause.
- Blood work and cerebrospinal fluid (CSF) studies. These tests may help detect uncommon causes of INO.
Treatment of internuclear ophthalmoplegia will depend upon the underlying condition causing it. Sometimes the condition may be the first sign that a person has multiple sclerosis, which will involve further neurological treatment. Recovery from a stroke also varies greatly. Patients whose internuclear ophthalmoplegia is caused by infection, reaction to medication or trauma usually recover completely. Possible treatment plans may include:
- Botox injections for strabismus (unaligned eyes). When injected into the muscles around the eyes, Botox can help reduce misalignment.
- Corrective lenses, including Fresnel prism lenses
- Surgery to correct strabismus for patients with WEBINO
Patients will continue to follow up with their doctor to monitor symptom progress and to determine if additional treatments are necessary.