Strabismus: Types, Causes, Symptoms
What is strabismus?
When your eyes do not line up or align with one another, or when one eye is turned in a direction that is different from the fellow eye, you have strabismus (misaligned eyes). Ideally, the 8 muscles that regulate eye movement collaborate and point both eyes in the same direction. If you have strabismus, you would have problems with eye movement control as well as problems with eye alignment. It is estimated that 4% of the U.S. population, or about 13 million people, have strabismus [1].
Strabismus can be classified based on the direction of the turned or misaligned eye:
- Inward turning (esotropia)
- Outward turning (exotropia)
- Upward turning (hypertropia)
- Downward turning (hypotropia)
To better identify the cause and treatment of strabismus, consider the following questions.
- Did this issue abruptly come about or did it happen over a longer time period?
- Did this issue happen within the first months of life, or later on?
- Is only one eye affected?
- Is it the degree of turning small or large?
- Does this issue happen all the time or only occasionally?
- Is a family history of strabismus present?
What are the types of strabismus?
There are various types of strabismus. The two most prevalent types are:
- Accommodative esotropia: This condition that usually happens in the first few years of life also happens in cases of uncorrected hypermetropia (farsightedness) and family history of strabismus. As the direction in which the eyes are pointing affects your capability to focus, your eyes may turn inward due to the extra energy required to ensure that faraway objects or people remain in clear focus. The symptoms of this type of strabismus are double vision, covering one eye when looking at nearby objects, and turning the head. Glasses, eye patching and/or surgery on the muscles of one or both eyes are common treatment options.
- Intermittent exotropia: This kind of strabismus describes a condition whereby one eye will focus on a target while the other eye is pointing outward. The symptoms of this type of strabismus may include double vision, headaches, reading challenges, eyestrain, and covering one eye when under bright light conditions or when looking at faraway objects. Intermittent exotropia can happen regardless of age. Glasses, patching, eye exercises and/or surgery on the muscles of one or both eyes are prevalent treatment options.
Infantile esotropia is a third kind of strabismus that is characterised by a significant amount of inward turning of both eyes. This condition usually happens in infants under 6 months of age, particularly when the child is looking far away and up close. While inward turning may start on an irregular basis, it can become increasingly regular. Surgery on the muscles of one or both eyes to address the alignment is the treatment for this type of strabismus.
What causes strabismus?
Most strabismus is caused by an abnormality of the neuromuscular control of eye movement. Oftentimes, strabismus is inherited, with about 30% of children with strabismus having a family member with a similar problem.
Other conditions linked to strabismus include:
- Untreated refractive errors
- Poor vision in one eye
- Cerebral palsy
- Down syndrome
- Hydrocephalus (a congenital disease that culminates in an accumulation of fluid in the brain)
- Brain tumours
- Stroke
- Head injuries, which can damage the area of the brain responsible for control of eye movement and the eye muscles
- Neurological (nervous system) problems
- Graves’ disease (excess of thyroid hormone)
When do the symptoms appear?
A 3 to 4-month-old infant’s eyes should be able to concentrate on small objects, and the eyes should be straight and well-aligned. A 6-month-old infant should be able to fixate properly on both nearby and faraway objects.
While strabismus most often surfaces by the time a child reaches the age of 3 years old. Older children and even adults can develop strabismus. The abrupt manifestation of strabismus, particularly with double vision, in an older child or adult could allude to a more deep-seated neurologic disorder. Seek immediate attention if this is observed.
Note that a symptom called pseudostrabismus (false strabismus) can make it look like an infant has esotropia (inward turning of the eye/s) when reality has it that the eyes are towards the same direction. Pseudostrabismus can be due to extra skin enveloping the inner corners of the eyes and/or a flat nasal bridge. The eyes will no longer appear crossed once a baby grows older. Pseudo vs an actual strabismus can be ruled out with a simple test conducted by an eye care professional.
How is diagnosed?
If you are older than 4 months of age and seem to have strabismus, you should have a comprehensive eye examination by a paediatric eye care professional. The examination may include the following:
- Questioning of your medical and family history
- Visual acuity test
- Refraction test with corrective lenses
- Alignment tests
- Eye focus tests
- Examination after dilation (widening) of the pupils to evaluate internal eye structures
How is strabismus treated?
The treatment for strabismus can include:
- Corrective lenses in the form of contact lenses or glasses: Corrective lenses would help your eyes as less focusing effort would be needed to look at objects clearly, especially when you have uncorrected refractive errors in your eye.
- Prism lenses: These special lenses can bend light entering your eye, thus decreasing the amount of turning your eye must do to look clearly at objects.
- Orthoptics (eye exercises): Some types of strabismus can be treated with this option, such as convergence insufficiency.
- Patching: Patching can treat both strabismus and amblyopia (lazy eye). You can enhance the control of the misalignment of your eye as well.
- Eye muscle surgery: Surgery with general anesthesia alters the length or position of eye muscles for correct eye alignment. Adjustable strabismus surgery, where the eye muscle positions are adjusted after surgery, can be prescribed as well.
Subtle changes may go unnoticed and only picked up by a trained professional, making regular comprehensive eye checks all the more important for timely identification, possible interventions and/or referrals to the respective health care professional when strabismus is observed.
References
[1] “Strabismus (crossed eyes): Types, causes, symptoms & treatment,” Cleveland Clinic. [Online]. Available: https://my.clevelandclinic.org/health/diseases/15065-strabismus-crossed-eyes. [Accessed: 31-Aug-2022].
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