Strabismus is a condition where the eyes do not align perfectly, looking in different directions simultaneously. It can manifest in various forms and degrees, often developing in childhood but also occurring in adults. This misalignment can impact how the brain processes visual information, potentially affecting vision and perception.
Understanding Eye Misalignment
Strabismus, also known as “crossed eyes” or “walleye,” involves an imbalance in the muscles that control eye movement. Six muscles attach to each eye, receiving signals from the brain to direct their movements. In individuals with strabismus, these muscles do not work together effectively, causing one eye to turn inward, outward, upward, or downward while the other eye remains focused straight ahead. This misalignment can be constant or intermittent, appearing when a person is tired, ill, or engaged in close work. When the eyes are misaligned, the brain receives two different images, which can initially lead to double vision or confusion. Over time, particularly in children, the brain may learn to ignore the image from the misaligned eye to avoid double vision, which can result in reduced vision in that eye, known as amblyopia or “lazy eye.”
Different Forms of Misalignment
Eye misalignment can present in distinct ways, categorized by the direction of the eye turn. Esotropia describes an inward turning of one or both eyes, often giving a “cross-eyed” appearance. This can be constant or intermittent, affecting one eye or alternating. Conversely, exotropia involves an outward turning of one or both eyes, sometimes referred to as “wall-eyed.” Exotropia can also be constant or intermittent, becoming more noticeable when a person is tired or looking into the distance.
Vertical misalignments include hypertropia, where one eye turns upward. This is the least common type of strabismus. The opposite condition, hypotropia, involves one eye turning downward. Both hypertropia and hypotropia can affect binocular vision and depth perception.
Common Causes of Misaligned Eyes
Strabismus can arise from various factors impacting the system that controls eye movement. A primary cause is an imbalance in the eye muscles, making them too weak or too strong to work together. Problems with the nerves that transmit signals to these muscles, or issues within the brain’s control center that directs eye movements, can also lead to misalignment. Certain neurological conditions, such as cerebral palsy or stroke, can cause strabismus, particularly in adults where stroke is a common factor.
Uncorrected refractive errors, like significant farsightedness (hyperopia), can contribute to strabismus. To focus clearly on near objects, the eyes may over-converge, leading to an inward turn. Genetic predisposition also plays a role, as strabismus can run in families, increasing the likelihood of children developing the condition if parents or siblings are affected. Other medical conditions, including thyroid eye disease, or physical trauma to the eye or head, can also disrupt eye alignment.
Diagnosis and Detection
Identifying strabismus involves a comprehensive eye examination. This includes assessing visual acuity to determine the clarity of vision in each eye. Eye doctors also perform specific tests to check eye alignment and movement. The cover-uncover test, for instance, involves covering one eye and then uncovering it to observe any shifting or movement in the other eye, revealing a misalignment. Another diagnostic tool is the corneal light reflex test, which checks where light reflects from the cornea to assess eye alignment.
Early detection of strabismus is important, especially in children. Prompt diagnosis allows for earlier intervention, which can improve the correction of misalignment and prevent the development of associated vision problems like amblyopia. Infants whose eyes consistently appear misaligned after four months of age should be examined by an eye doctor.
Treatment Approaches
Treating strabismus aims to correct eye alignment and improve visual function, often tailored to the specific type and cause. One common approach involves prescribing eyeglasses or contact lenses, particularly when refractive errors like farsightedness contribute to the eye turn. Corrective lenses can help the eyes focus properly and reduce the need for excessive focusing efforts that might lead to misalignment.
Vision therapy, which includes a series of eye exercises, is another option. This therapy works to improve eye-brain coordination, strengthen eye muscles, and enhance binocular vision and depth perception. Patching or atropine eye drops may be used, especially if amblyopia (lazy eye) has developed as a result of strabismus. Patching the stronger eye or using atropine drops to blur its vision encourages the brain to rely more on the misaligned or weaker eye, thereby strengthening it.
Surgical correction of the eye muscles is also a treatment for strabismus. During this procedure, an ophthalmologist may loosen or tighten specific eye muscles to reposition them, helping the eyes align properly. Surgery can improve the cosmetic appearance of the eyes and sometimes helps restore or improve the eyes’ ability to work together. In some cases, vision therapy may be recommended after surgery to further refine eye coordination.