Uncrossing the Truth Behind Strabismus
Strabismus is misalignment of the eyes. There are six muscles, called the extraocular muscles, that control the movement and position of the eyes. The muscles of the right eye need to work in conjunction with the appropriate muscles of the left eye to ensure the eyes stay aligned and work smoothly together. If one of the muscles is underactive or overactive, it can interfere with the balance of the muscles, which causes an eye to turn in the wrong direction.
One or both eyes can be affected depending on whether the strabismus alternates back and forth between the eyes. The eye with strabismus could be directed out to the side, in towards the nose, up or down. In some cases, the eye can even be in a combination of directions (e.g., outward and upward). The eye turn can be constant (happening all the time) or intermittent (only occurring occasionally.)
Occurrence of Strabismus
According to the American Optometric Association, approximately 2 to 5 percent of the general population has strabismus. Children can be born with a congenital form of strabismus while some adults acquire it later in life. The cause of strabismus usually varies between the congenital and acquired forms. Both can be attributed to either an anatomical or neurological problem.
Signs and Symptoms of Strabismus
The most obvious sign is viewing the eyes in a misaligned state. Some people might tilt or turn their head to compensate for the strabismus.
Symptoms vary based on the severity of the strabismus and age of the individual upon first having strabismus. Double vision, headaches, eyestrain, and getting easily fatigued when reading are the most common symptoms.
If strabismus develops in adulthood, the most prevalent symptom is double vision. This is caused by the eyes looking at two different images. If one of the eyes is looking in the wrong direction, or even just slightly off-target, the brain is unable to fuse the two images together and double vision occurs. Children might not be able to communicate they are seeing double. To fix the problem, a child might cover or close an eye while reading. This temporarily eliminates the double vision and the child is able to carry on without verbalizing the symptoms to a parent.
Children have a “plastic” or moldable brain for several years after birth. This means if a child is born with strabismus, the brain can sometimes rewire itself to deal with the different images viewed by the eyes. Rather than seeing double, the brain will turn off the connection to the misaligned eye and ignore the image from that eye. When the connection between the eye and brain is not functioning, the brain can no longer process 20/20 vision from the affected eye. This is defined as strabismic amblyopia, or more commonly known as a “lazy eye.”
Types of Strabismus
Esotropia occurs when an eye turns inward. This is the most common type of strabismus for newborns. There is also a more specific type of esotropia, called accommodative esotropia, which occurs when the child has to overexert the focusing system. In accommodative esotropia, the eyes turn inward when trying to see clearly.
Exotropia occurs when an eye drifts or turns outward. This can be seen in people of all ages. Usually exotropia is intermittent and can be worse when the person is tired, daydreaming, under the influence of alcohol, or sick. A specific type of this strabismus is called sensory exotropia. This occurs when an individual suffers severe vision loss (retinal detachment, macular degeneration, glaucoma, etc.) and the eye turns outward over time from lack of usage.
Other less common types of strabismus include hypertropia (eye looking upwards), hypotropia (eye looking downward), and cyclotropia (rotational torsion of eyeball.)
The best way to determine if strabismus or any other problem is occurring is for a comprehensive eye examination, especially for children. Pediatrician and school vision screenings do not measure eye alignment, and a child with strabismus could therefore easily slip through the cracks of a screening. The earlier strabismus is diagnosed in children, the easier it is to treat and hopefully minimize the risk of visual complications in the future.
An eye doctor can assess the eye alignment using several different techniques, the most common being the “cover test.” Depth perception testing is another useful tool in diagnosing strabismus. If the eyes are not focusing together on the same object, depth perception will be hindered. Both eyes need to be looking at the same target in order to have depth perception, or binocular vision.
Sudden occurrence of strabismus in both children and adults can be a sign of a life-threatening neurological problem and should be addressed immediately.
The easiest treatment for strabismus is prescription glasses, however, this only works for a small fraction of people with strabismus. Children with accommodative esotropia may also benefit from bifocal glasses.
Prisms are a type of lens that shifts the image to the location of the eye. For example, if a person’s left eye is turned inward, a prism could be placed in the glasses to help move the patient’s visual surroundings in towards where the left eye is looking. This alleviates the double vision, but does not correct the strabismus. Prisms are also a good choice for people with a small vertical misalignment of the eyes.
Vision therapy (VT) is an excellent treatment option for an individual whose eye turns outward. It is much easier to train our eyes to converge (or turn in) versus teaching the eyes to diverge (turn outwards). VT is like physical therapy, but for the eye muscles and focusing system. Both children and adults can benefit from this form of treatment.
If none of these options are successful in alleviating symptoms, surgery can work for severe cases, however, it is possible that the strabismus will still be present or return over time.