The experience of noticing an eye that appears to wander or point in a different direction is a common visual phenomenon. This misalignment means the eyes are not working together, disrupting the ability to create a single, clear image. Understanding this condition involves learning its medical terminology, how it manifests, and the available interventions.
Strabismus The Medical Name for Eye Drift
The medical name for the condition where one eye drifts and the eyes do not look in the same direction is strabismus. This disorder of binocular vision means the eyes cannot focus on the same target simultaneously. Strabismus occurs because the six extraocular muscles surrounding each eye do not coordinate effectively. A problem in the complex system of brain signals and muscle movement prevents the eyes from maintaining proper alignment.
Strabismus is often confused with amblyopia, a related but distinct condition. Strabismus is the physical misalignment of the eye. Amblyopia, often called “lazy eye,” is a functional vision problem where the brain ignores input from the misaligned eye to avoid seeing double.
If misalignment occurs during early childhood, the brain suppresses the image from the turned eye. If left untreated, this can lead to permanently reduced vision in that eye. Strabismus is the cause, and amblyopia is the resulting loss of visual acuity that cannot be corrected with glasses alone.
Classifying the Direction of Misalignment
Eye drift is classified based on the direction the misaligned eye turns. These classifications use Greek prefixes combined with the suffix “-tropia,” which denotes a manifest, or constantly visible, deviation. Misalignment can occur horizontally, vertically, or both.
When the eye turns inward, toward the nose, the condition is called esotropia, often referred to as being “cross-eyed.” Conversely, an eye that turns outward, away from the nose, is classified as exotropia. These are the most common types of horizontal strabismus.
Vertical misalignments also have specific names. Hypertropia describes the condition where the eye drifts upward, positioning it higher than the other eye. If the eye turns downward, the condition is known as hypotropia.
The misalignment can be constant or intermittent, appearing only when the person is tired or focusing intently. In some cases, the misaligned eye may alternate between turning in and turning out.
Common Causes and Risk Factors
Strabismus is rooted in a dysfunction of the neuromuscular control system governing eye movement. The six extraocular muscles must work in synchrony, but issues with the muscles or the cranial nerves that supply them cause a lack of coordination. Damage to the third, fourth, or sixth cranial nerves, for example, can impair muscle function and lead to paralytic strabismus.
A significant cause, particularly esotropia in children, is uncorrected farsightedness (hyperopia). To focus clearly, a farsighted person’s eyes must work harder. This excessive focusing effort can trigger the eyes to cross inward. Correcting this refractive error with glasses often resolves the misalignment.
Risk factors increase the likelihood of developing strabismus. A strong family history suggests a genetic predisposition. Strabismus is also observed in individuals with medical conditions affecting the brain and nervous system, such as cerebral palsy, Down syndrome, and stroke. Onset in an adult often signals a neurological event, like a stroke or head trauma, impacting eye coordination.
Diagnosis and Treatment Options
Diagnosis begins with a comprehensive eye examination, including specialized tests to assess eye alignment and movement. The cover-uncover test is a fundamental procedure where the doctor covers one eye and observes the movement of the other eye to detect a manifest deviation. Visual acuity tests measure the sharpness of vision, and refraction determines if a refractive error is contributing to the misalignment.
Treatment strategies aim to improve eye alignment, restore binocular vision, and treat any resulting amblyopia. For strabismus caused by refractive error, eyeglasses or contact lenses are the first line of treatment. Special prism lenses can be incorporated into glasses to bend light, reducing the amount the eye must turn and minimizing double vision.
If amblyopia is present, treatments include patching the stronger eye or using atropine eye drops to blur its vision. These methods force the brain to rely on the misaligned eye, helping to improve its vision. Vision therapy, a structured program of eye exercises, can also be prescribed to strengthen the eye-brain connection and improve coordination.
When non-surgical options are insufficient, eye muscle surgery is recommended to physically realign the eyes. This procedure adjusts the length or position of the extraocular muscles so the eyes point in the same direction. Alternatively, botulinum toxin (Botox) injections can temporarily weaken an overactive eye muscle.