Esotropia is a specific form of strabismus where one or both eyes turn inward, toward the nose. Commonly referred to as “crossed eyes,” this condition results from a misalignment where the muscles controlling eye movement are not properly synchronized. The inward turn can be constant or intermittent, affecting one eye or alternating between both. While frequently seen in infants and young children, esotropia can develop at any age from various underlying causes.
Underlying Causes and Types of Esotropia
Esotropia is categorized by its origin and when it appears. One of the earliest forms is infantile or congenital esotropia, which develops within the first year of life. The exact cause is not fully understood, but it is believed to involve an abnormality in the brain’s ability to coordinate the eyes. These infants have a large and constant eye turn that requires early intervention.
The most common form is accommodative esotropia, which is directly linked to significant farsightedness (hyperopia). When someone is farsighted, their eyes exert extra focusing effort (accommodation) to see clearly. This focusing action is linked to a signal for the eyes to converge, or turn inward, which can cause over-convergence in those with significant hyperopia. This type usually appears between 18 and 36 months of age.
A third category is acquired esotropia, which appears later in childhood or adulthood. This form can result from underlying medical issues. Neurological conditions such as a stroke, head injury, or nerve damage can disrupt the signals that control eye muscles. Other health problems like diabetes or thyroid disease can also lead to the development of esotropia.
Diagnosis and Professional Evaluation
A professional eye examination, often by a pediatric ophthalmologist, is required to diagnose esotropia. The evaluation begins with a detailed patient history, including when the eye turn was first noticed and if there is a family history of strabismus. The specialist then performs a series of tests to assess eye alignment and function. These evaluations distinguish true esotropia from pseudoesotropia, a condition where a wide nasal bridge and skin folds give the appearance of crossed eyes in an infant.
Two primary tests are the corneal light reflex test (Hirschberg test) and the cover test. In the Hirschberg test, the examiner shines a light into the patient’s eyes and observes the reflection on the cornea. If the eyes are aligned, the reflection will appear in the same position in the center of each pupil; in esotropia, the reflection in the turned eye will be displaced outward.
The cover test helps determine the eye turn’s presence and nature. The examiner has the patient focus on a target while covering one eye and watching the other for movement. If the uncovered eye moves to pick up fixation, it indicates a manifest misalignment (a tropia). A variation called the cover-uncover test helps identify a latent deviation (a phoria) by observing the eye that was covered for movement after the occluder is removed.
Treatment Approaches
Treatment is customized to the specific type and cause, with the goals of aligning the eyes and developing normal vision. For accommodative esotropia, the first and most common treatment is corrective eyeglasses. By correcting the underlying farsightedness, the glasses reduce the need for excessive focusing effort, which in turn allows the eyes to straighten. Bifocal lenses may be prescribed if the eye turn is more pronounced when looking at near objects.
When esotropia leads to amblyopia, or “lazy eye,” treatments are directed at improving vision in the weaker eye. This is accomplished through patching, where the stronger eye is covered daily to force the brain to use and strengthen the weaker eye. As an alternative to patching, atropine eye drops can be used to temporarily blur the vision in the stronger eye, achieving a similar outcome. These methods treat amblyopia, not the eye turn itself.
For cases not corrected by glasses, like infantile esotropia or large-angle deviations, surgery on the eye muscles is often necessary. The procedure involves repositioning one or more of the six muscles attached to the outside of the eye to improve alignment. The surgeon may tighten a weak muscle or loosen a tight one to rebalance the forces acting on the eye. While often successful, some individuals may require more than one surgery to achieve the desired alignment.
Potential Complications of Untreated Esotropia
Untreated esotropia, particularly in early childhood, can lead to lasting vision problems. The most significant complication is the development of amblyopia. When one eye constantly turns inward, the brain receives two different images and, to avoid double vision, begins to ignore or suppress the input from the misaligned eye. This suppression hinders the development of vision in that eye, resulting in permanently reduced visual acuity if not addressed early.
Another consequence is the loss of binocular vision, the ability of the eyes to work together to create a single, 3-D image. Proper eye alignment is necessary for the brain to fuse the images from each eye. Without it, an individual loses stereopsis, the specific term for 3-D vision and depth perception. This can affect a person’s ability to judge distances, which can impact activities like catching a ball, navigating stairs, or driving.