Strabismus, commonly known as a “wandering eye,” is a visual disorder where the eyes do not look in the same direction simultaneously. It affects the coordination of eye movements and is present in an estimated 2 to 4 percent of the population. Both eyes fail to align correctly when focusing on an object, causing one eye to drift away from the visual target. This lack of coordination can be present constantly or appear only sometimes, making early detection important for visual development.
Defining Strabismus and Its Types
Strabismus is fundamentally a failure of the six extraocular muscles surrounding each eye to work together in perfect synchrony. These muscles receive signals from the brain, and when the control center or the muscles themselves are impaired, the eyes cannot hold their alignment. This misalignment is classified based on the direction the misaligned eye turns.
The most common classification is based on horizontal deviation. Esotropia, often called “crossed eyes,” occurs when the eye deviates inward toward the nose. Conversely, Exotropia causes the eye to drift outward away from the nose, sometimes called “wall-eyed.”
Vertical misalignments also occur: Hypertropia is when the eye turns upward, and Hypotropia is when it turns downward. Strabismus is further categorized by its presence: Constant Strabismus means the misalignment is present all the time, whereas Intermittent Strabismus means the eye drifts only occasionally, perhaps during times of fatigue or illness. Intermittent Exotropia is the most frequent form of intermittent strabismus.
Underlying Causes and Risk Factors
The origin of Strabismus is typically rooted in an abnormality of the neuromuscular control system that directs eye movement. This includes issues with the brain’s control centers or damage to the cranial nerves that supply the eye muscles. For example, damage to the third, fourth, or sixth cranial nerves can cause a paralytic strabismus with limited eye movement.
A significant cause in children is uncorrected refractive error, specifically farsightedness, or hyperopia. The body’s focusing system is linked to the eye-pointing system, so the extra effort needed to focus can cause the eyes to over-converge and turn inward, leading to a condition called accommodative esotropia. Family history also plays a role, suggesting a genetic predisposition for the condition.
Certain systemic medical conditions increase the risk of developing Strabismus because they can affect the neurological system. Individuals with Down syndrome, cerebral palsy, or a history of stroke or severe head injury have a higher incidence of eye misalignment. In adults, the sudden onset of strabismus is often associated with a stroke or other neurological event.
Recognizable Symptoms and Visual Effects
The most obvious sign of Strabismus is the visible misalignment of one eye, which may turn in, out, up, or down. People with this condition may exhibit observable behaviors like frequent squinting, closing one eye, or tilting the head to try and align the images they are seeing. These physical signs are often an unconscious attempt to manage the visual confusion caused by the eye turn.
The serious visual effect in children is the risk of developing Amblyopia, commonly called “lazy eye.” To avoid the double image created by the misaligned eye, a child’s developing brain may suppress the input from the turned eye. If this continues, the visual pathways for that eye do not develop correctly, leading to a permanent reduction in visual acuity.
If Strabismus develops in older children or adults, the visual system is already mature, and the brain cannot easily suppress the second image. The primary visual effect in these cases is Diplopia, or double vision, which can be highly disruptive to daily activities. The misalignment also impairs binocular vision, leading to a loss of depth perception, or stereopsis.
Corrective Measures and Treatment Paths
The primary goal of Strabismus treatment is to restore proper eye alignment and achieve functional binocular vision. The first step often involves correcting any underlying vision problems. Prescription eyeglasses alone can resolve accommodative esotropia by reducing the need for excessive focusing effort. Glasses may also incorporate prism lenses, which bend light to shift the image onto the correct part of the retina, helping to fuse the two images and relieve double vision.
If Amblyopia has developed, treatment focuses on forcing the brain to use the weaker eye, most commonly achieved through patching. The stronger eye is covered for a specific number of hours each day, which strengthens the visual pathways of the misaligned eye and improves its acuity. An alternative to patching is using atropine eye drops in the stronger eye to temporarily blur its vision, similarly encouraging the use of the weaker eye.
When non-surgical methods are insufficient, surgery on the extraocular muscles may be recommended to physically realign the eyes. The procedure involves adjusting the tension by weakening or strengthening specific muscles through recession or resection. Because the visual system is most adaptable early on, intervention should begin as soon as Strabismus is diagnosed to maximize the chances of preventing permanent vision loss and achieving full binocular function.