Monocular exotropia is a form of eye misalignment, or strabismus, where one eye deviates outward while the other eye remains focused on a target. The term “monocular” signifies that it is consistently the same eye that turns, which distinguishes it from other types of strabismus where the affected eye might alternate. While often identified in infants and young children, it can develop in adults as well.
Symptoms and Causes of Monocular Exotropia
The most apparent sign of monocular exotropia is the visible outward turn of one eye. This deviation can become more pronounced when an individual is tired, ill, daydreaming, or in bright sunlight, often causing them to squint or close one eye. People with this condition may also experience eye strain, headaches, and blurry or double vision (diplopia). Some may tilt their head to compensate for the misalignment.
The condition stems from an imbalance in the six muscles that control eye movement, as the brain struggles to coordinate them correctly, leading one eye to drift outward. There is also a genetic component, as the condition can run in families. In other cases, it can be related to uncorrected refractive errors like farsightedness or nearsightedness, or problems with nerve signals from the brain to the eye muscles.
The Diagnostic Process
Diagnosing monocular exotropia involves a comprehensive examination by an optometrist or ophthalmologist to determine the nature and severity of the eye turn. A primary diagnostic tool is the cover test, where the doctor covers each eye one at a time. By observing how the uncovered eye moves to focus, the specialist can detect the presence and magnitude of the deviation.
Further tests are conducted to assess the condition’s impact on vision. A visual acuity test, using a standard eye chart, measures how clearly each eye can see and checks for differences between them. The doctor will also evaluate ocular alignment and eye movements to understand how the eyes work together. These assessments help confirm the diagnosis and formulate a treatment plan.
Treatment Approaches for Monocular Exotropia
Treatment for monocular exotropia is tailored to the individual’s age and the severity of the eye turn, often beginning with the least invasive options. For some, corrective eyeglasses or contact lenses are sufficient to address underlying refractive errors that contribute to the misalignment. Special prism lenses may also be added to glasses to help align the images sent to the brain, which can reduce double vision.
When glasses alone are not enough, non-surgical therapies are often recommended. Occlusion therapy involves placing a patch over the stronger, properly aligned eye, a common method used in children. This encourages the brain to use the deviating eye, strengthening its muscle control. Vision therapy consists of prescribed eye exercises designed to improve eye coordination and the brain’s ability to fuse images from both eyes.
In more significant cases, surgery may be the most effective solution. The procedure involves adjusting the tension of the eye muscles to improve alignment. A surgeon can tighten or loosen specific muscles on the outside of the eye to change its position. Surgery is often followed by vision therapy to help the eyes learn to work together post-operatively.
Potential Complications Without Treatment
Untreated monocular exotropia can lead to permanent vision problems. A primary risk is the development of amblyopia, or “lazy eye.” To avoid double vision, the brain may start to suppress visual information from the misaligned eye. This suppression can hinder the normal development of vision in that eye, leading to a permanent reduction in visual acuity that glasses cannot correct.
Another complication is the loss of binocular vision, which is the ability of the eyes to work together to create a single, unified image. Without proper alignment, the brain cannot fuse the two separate images, resulting in poor stereopsis, or 3D vision. This loss of depth perception can impact daily activities that require judging distances, such as playing sports, navigating stairs, or driving.