Eye movement disorder
Most issues with vision are due to the lenses of the eye not focusing properly, but some people develop problems because their eye muscles do not work correctly. Eye movement disorders are caused by involuntary muscle movements around the eyes, and they can result in many vision issues.
Definition & Facts
Eye movement disorders is a broad category of vision disorders that result from improper muscle movement around the eyes. Though there are many different types of eye movement disorders, they generally fall into a few categories.
Strabismus is a disorder that happens when the muscles of each eye do not work together, causing one eye to turn slightly inward or outward when a person is focusing on an object. Another common disorder is nystagmus which causes the eyes to make fast, uncontrollable movements instead of fixing on the object a person is trying to focus on.
Symptoms & Complaints
Strabismus can cause an eye to either drift inward, outward, upward, or downward instead of looking at the object of focus. Patients with strabismus tend to experience double vision (diplopia) when their eye crosses.
If the strabismus is left untreated, the brain may start to ignore input from the eye that does not focus on the desired object. This results in vision loss and a lack of depth perception, and the eye that is not used by the brain will drift even more, resulting in what is called a "lazy eye."
Nystagmus is another type of movement disorder that makes the eyes move in repetitive motions. This condition is very noticeable to both the patient and the observer. Eyes often look side to side in rapid, fluttering motions, but sometimes, patients may have repetitive movements that rotate, go sideways, or move up and down. When this happens, it is often very difficult for the patient to see, and many develop nausea or vertigo due to the shifting vision.
Eye movement disorders can be congenital disorders which means that they are present at birth, or they can develop during adulthood. There are many different potential causes of an eye movement disorder, but most are related to issues with the muscles, nerves, and brain. Certain genetic mutations with the FRMD7 gene can cause children to be born with eye movement disorders. Other congenital conditions, such as cerebral palsy and albinism, can also cause infants to have eye disorders.
However, there is not always an underlying cause for strabismus; sometimes it occurs because some infants do not automatically learn to focus both of their eyes together. In adults, a traumatic brain injury, stroke, or brain tumor can cause eye movement disorders.
Strabismus can develop after a person has an eye injury, botulism, or shellfish poisoning. It may also develop because a person has Prader-Willi syndrome, Graves' disease, diabetes mellitus, or Guillain-Barré syndrome.
Nystagmus can be acquired after a person starts using certain medications and drugs, including alcohol, amphetamines, selective serotonin reuptake inhibitors (SSRIs), benzodiazepines, or lithium. Nystagmus is also a secondary symptom of Whipple's disease, multiple sclerosis, Tullio phenomenon, Wernicke's-Korsakoff syndrome, and Ménière's disease.
Diagnosis & Tests
Though it seems like diagnosis of eye movement disorders would be relatively straightforward on the basis of observable symptoms, it is not always simple for mild cases. A nystagmus diagnosis can only be done if it is determined that the eye movements are both repetitive and involuntary. The most common test for nystagmus is a caloric reflex test that introduces cold or warm water or air into the ear canal. This imbalance in temperatures triggers nystagmus almost immediately.
Eye movements can be recorded either with electronystagmography that use external electrodes or a videonystagmography that uses external cameras. These recorded eye movements are then analyzed to see if they are indeed repetitive and moving in the nystagmus patterns.
Strabismus diagnosis usually happens during a basic eye examination, and it just requires a simple test of covering each eye while observing eye function. This is called the cover test, and it can be used to figure out just how severe the strabismus is. Further testing for eye movement disorders mostly focuses on determining the cause.
Treatment & Therapy
The treatment for an eye movement disorder will depend on the type of disorder and reason for the disorder. In mild cases, strabismus only requires a child to wear an eye patch over the dominant eye to strengthen the weaker eye. Injections of the botulinum toxin can temporarily paralyze the stronger eye, resulting in the same effect as wearing an eye patch.
Strabismus can also be managed by wearing special eyeglasses. In more severe strabismus cases, surgery can be used to change the position of an eye muscle and move the eyes into balance and focus. If a patient has nystagmus due to medication or substance abuse, stopping use may result in the cessation of symptoms.
Nystagmus can also be managed with certain drugs, including baclofen, gabapentin, memantine, and levetiracetam, and all of these drugs work as an anticonvulsant. Surgery can also provide some benefits by weakening the overactive eye muscles.
Some patients benefit from physical therapy and occupational therapy that teaches them compensating strategies for living with shaky eye vision. Most treatments for eye movement disorders provide at least some relief. However, in cases where the eye movement disorder is due to an underlying medical condition, it may not be entirely curable.
Prevention & Prophylaxis
Certain eyeglasses may help to prevent strabismus among infants. The best way a person can prevent eye movement disorders from worsening is by getting regular eye exams and immediately treating any problems that are discovered.