The condition commonly referred to as “going cross-eyed” is medically termed strabismus. While it is not acutely dangerous, a persistent misalignment of the eyes necessitates prompt medical attention and evaluation by an eye care professional. Newborns may exhibit transient eye crossing as their visual system develops, but any deviation that continues beyond four to six months of age is considered abnormal. For older children and adults, the onset of strabismus is a significant symptom indicating an underlying muscular, neurological, or refractive problem.
Understanding Strabismus
Strabismus is defined as a visual disorder where the eyes fail to align properly and point in different directions when focusing on an object. This lack of parallel alignment means that the two eyes are unable to fixate on the same point simultaneously, disrupting binocular vision. The popular term “cross-eyed” specifically refers to esotropia, where one or both eyes turn inward toward the nose.
Strabismus is not limited to inward turning and can manifest in several distinct ways. When an eye turns outward, away from the nose, the condition is called exotropia. Vertical deviations also occur, with hypertropia describing an eye that turns upward and hypotropia describing an eye that turns downward. This misalignment may be constant or intermittent, only appearing when the person is tired, ill, or performing close-up work.
Common Causes of Misalignment
The primary mechanism behind strabismus involves a dysfunction in the coordination between the six extraocular muscles surrounding each eye. These muscles receive signals from the brain via cranial nerves. A problem with the nerve signal, the muscle, or the brain’s control center leads to an imbalance in muscle tension, causing one eye to drift off target.
A frequent cause of strabismus, particularly in children, is a significant uncorrected refractive error, most commonly farsightedness, or hyperopia. The act of focusing intensely to clear a blurry image is neurologically linked to the eye’s convergence mechanism, which naturally pulls the eyes inward. In a highly farsighted child, this excessive focusing effort, known as accommodation, can trigger an over-convergence, resulting in accommodative esotropia.
Strabismus is categorized as congenital, present at birth or developing within the first six months of life, or acquired, developing later due to other factors. Acquired strabismus in adults or older children can signal a more serious underlying issue, such as trauma, a neurological condition, or an acute event like a stroke. Graves’ disease, cerebral palsy, and head injuries are also recognized risk factors for acquired strabismus.
Consequences and Necessary Interventions
The greatest long-term consequence of untreated strabismus in childhood is amblyopia, commonly known as a lazy eye. To avoid the confusion and double vision (diplopia) caused by the misaligned images, the developing brain suppresses the visual input from the turned eye. If this suppression continues during the critical period of visual development, the neural pathways fail to develop properly, leading to permanently reduced visual acuity.
The misalignment prevents the eyes from achieving binocular vision, which is the ability to fuse the two separate images into a single three-dimensional perception. The loss of this fusion results in poor depth perception and impaired stereo vision. For adults who develop strabismus suddenly, the brain is usually unable to suppress the image, leading immediately to persistent double vision.
Intervention aims to achieve ocular alignment and preserve or restore vision and binocular function. The initial step often involves prescribing corrective glasses, which can resolve accommodative esotropia by eliminating the need for excessive focusing. If amblyopia is present, treatment typically involves patching the stronger eye to force the weaker eye to work and strengthen its connection to the brain. If glasses or vision therapy are insufficient, surgery on the extraocular muscles may be necessary to adjust muscle tension and physically realign the eyes.