Strabismus is a disorder in which the eyes are misaligned. It may be very obvious, barely noticeable, or impossible to detect except by an eye care professional. It can affect only one eye, or it can alternate between the two eyes. Strabismus can also be constant or intermittent.
There are four types of strabismus, based on the direction of the misaligned eye:
- Exotropia - One eye points out ("wall-eyed").
- Esotropia - One eye points in ("cross-eyed").
- Hypertropia - One eye points up.
- Hypotropia - One eye points down.
Strabismus frequently causes amblyopia - a vision disorder where the brain ignores images from the affected eye - or, in some cases, double vision.
What causes strabismus?
There are six muscles (called the extraocular muscles) that surround each eye and control eye position. The actions of these muscles must be perfectly balanced in order for our eyes to maintain proper alignment as we look straight ahead and in different directions.
Strabismus is usually due to a congenital imbalance of the effect of these six muscles on the eye. In some cases, strabismus (particularly esotropia) may be caused by an over-action of one or more of these muscles due to uncorrected farsightedness.
How common is strabismus?
About 4 percent of the U.S. population has strabismus.
Who is at risk?
Anyone can have strabismus. It occurs equally in males and females. A family history of strabismus is a risk factor.
What are the symptoms of strabismus?
In moderate or severe cases of strabismus, the obvious sign of the disorder is misalignment of the eyes. However in some cases, the degree of eye turn is so slight that it goes unnoticed.
Other signs or symptoms of strabismus include:
- Amblyopia (decreased visual acuity) in the turned eye.
- Squinting one eye in bright light.
- Uncoordinated eye movements.
- Tilting the head or turning it to one side when looking straight ahead.
How is strabismus detected?
Moderate and severe cases of strabismus can be easily detected by simply observing a person and noting whether or not their eyes appear properly aligned. But in many cases of strabismus, the degree of eye turn is so small that it cannot be detected without specialized testing by a trained eye care professional.
Many young children with mild cases of strabismus manage to pass their school vision screenings, especially of the eye turn is intermittent or alternating between the two eyes and there is no significant amblyopia. Therefore, all children should have a comprehensive eye exam by an Optometrist or Ophthalmologist prior to beginning school to rule out the presence of strabismus.
How is strabismus treated?
The first step in treatment of strabismus is a complete eye examination, including a Refraction to determine if corrective lenses are indicated. If farsightedness is expected, eye drops that dilate the pupils and relax the focusing muscle inside the eye may be used during the exam. This is because in some patients (youngsters in particular) it's impossible to determine the full amount of farsightedness without first making sure the focusing muscle inside the eye is completely relaxed.
For many farsighted children with esotropia, their strabismus can be effectively treated by simply wearing prescription lenses that fully correct their farsightedness.
Other treatment options for strabismus include:
For moderate and severe cases of strabismus, the only treatment option is surgery to align the eyes by adjusting the position of one or more of the extraocular muscles that control eye position.
If amblyopia is present, patching of the "good" eye may be prescribed before and/or after strabismus surgery to improve the visual acuity of the turned eye and help maintain proper eye alignment after surgery.
In mild cases of strabismus (especially when the eye turn is intermittent), it may be possible to improve eye alignment and eye teaming non-surgically with vision therapy.
Vision therapy consists of a program of specific visual activities prescribed by an eye care professional to improve binocular vision (i.e. the ability of the two eyes be properly aligned and to see equally, simultaneously and comfortably as a team). The therapy typically takes place over a period of weeks or months and is supervised by an eye doctor or a trained assistant.
Often a combination of surgery and vision therapy is the best treatment plan for strabismus.
Regardless of which type of treatment is used, it's best to detect and treat strabismus as early as possible in a person's lifetime for the best possible results.
