Being cross-eyed means your eyes don’t point in the same direction at the same time. One eye looks straight ahead while the other turns inward, outward, up, or down. The medical term is strabismus, and it affects roughly 2% of the global population. It can appear at birth, develop during childhood, or show up for the first time in adulthood.
How Eye Alignment Normally Works
Each eye is controlled by six small muscles that work together to aim both eyes at the same target. Your brain coordinates these muscles so precisely that both eyes lock onto the same point, and the two slightly different images merge into one clear picture with depth perception. Strabismus happens when this coordination breaks down.
Most of the time, the problem isn’t with the muscles themselves. It’s with the brain signals that control them. The nerves carrying instructions from your brain to your eye muscles may not function correctly, causing one eye to drift. Less commonly, the eye muscle itself is damaged or restricted. Head injuries, for example, can disrupt the brain area responsible for eye movement, the nerves that relay those signals, or the muscles directly.
Types of Eye Misalignment
The direction the misaligned eye turns determines the type:
- Esotropia: the eye turns inward, toward the nose. This is what most people picture when they hear “cross-eyed” and is the more common form in young children.
- Exotropia: the eye turns outward, away from the nose. Sometimes called “wall-eyed,” this is actually the most common type globally, with a prevalence of about 1.2% compared to 0.8% for esotropia.
- Hypertropia: the eye drifts upward.
- Hypotropia: the eye drifts downward.
The misalignment can be constant or intermittent, meaning the eye only drifts some of the time, often when you’re tired, stressed, or focusing at a particular distance. One eye may always be the one that turns, or the two eyes may alternate.
What It Feels Like Beyond Appearance
The visible misalignment is the most obvious sign, but strabismus affects how you see the world in ways that aren’t apparent to others. When the eyes point in different directions, each one sends a different image to the brain. In someone who develops strabismus suddenly, this produces double vision: you see two overlapping images, with the one from the misaligned eye typically appearing blurred.
The brain doesn’t tolerate this conflict for long. In children especially, the brain learns to ignore the image from the drifting eye, a process called suppression. This eliminates the double vision but comes at a cost. The suppressed eye gradually loses visual sharpness, a condition called amblyopia (often referred to as “lazy eye”). Children can suppress so effectively that the deviating eye’s vision deteriorates significantly if the condition isn’t caught early.
Regardless of age, strabismus reduces depth perception. Seeing in three dimensions requires both eyes working together, and when one eye is misaligned, your ability to judge distances suffers. You might struggle with tasks like pouring water into a glass, threading a needle, catching a ball, or parking a car.
Why It Develops in Children
Most strabismus appears before age 5. In many childhood cases, the exact cause is unclear, though genetics play a role. Children with a parent or sibling who has strabismus are at higher risk. Significant farsightedness is another common trigger: when a child’s eyes strain to focus on close objects, the extra effort can pull one eye inward, producing a form called accommodative esotropia.
Premature birth and low birth weight also increase risk, as do conditions that affect the brain or nervous system, such as cerebral palsy or Down syndrome.
One important note for parents: many babies appear cross-eyed in their first few months because of a wide, flat nasal bridge that makes the eyes look turned inward even when they’re perfectly aligned. This is called pseudostrabismus, and it’s harmless. As the face matures, the appearance resolves on its own. However, some children initially thought to have pseudostrabismus do turn out to have true strabismus, particularly if they have an intermittent deviation that’s easy to miss. Any eye crossing that persists beyond 4 months of age warrants a professional evaluation.
Why It Develops in Adults
Adults can develop strabismus for the first time, and it often points to an underlying health issue. Common causes include diabetes (which can damage the nerves supplying eye muscles), thyroid eye disease, stroke, brain tumors, and myasthenia gravis, a condition where nerve signals to muscles weaken over time. A head injury or trauma can also trigger sudden misalignment.
Some adults had strabismus as children that was treated or compensated for, only to see it return later in life as the eye muscles weaken with age. When strabismus appears suddenly in an adult, it almost always causes noticeable double vision, since the adult brain can’t suppress the second image the way a child’s brain can.
How It’s Diagnosed
The standard test is surprisingly simple. Called the cover-uncover test, it involves covering one eye at a time while you focus on a target. The examiner watches the uncovered eye to see if it shifts position when the other eye is blocked. If the eye moves to pick up focus, it was misaligned. The test can detect even subtle deviations that aren’t obvious from looking at someone’s face.
An eye doctor may also check the light reflex on the surface of each eye (shining a small light and seeing whether the reflection lands in the same spot on both pupils) and test your depth perception and visual acuity in each eye individually to assess whether amblyopia has developed.
Treatment Options
Treatment depends on the type, severity, and cause of the misalignment, along with the patient’s age.
Glasses and Prisms
When farsightedness is pulling the eye inward, corrective lenses alone can sometimes straighten the eyes completely. For double vision caused by smaller deviations, prisms can be built into your glasses. These specially angled lenses bend light before it enters the eye, redirecting the image so it lands on the correct spot despite the misalignment. Prisms work well for deviations up to a certain size. Smaller ones can be ground directly into standard lenses, while larger corrections use a thin, stick-on prism film. They eliminate double vision effectively, though some people notice slight reductions in contrast or clarity.
Patching and Vision Therapy
In children with amblyopia, patching the stronger eye forces the brain to use the weaker one, gradually restoring its visual acuity. This doesn’t fix the alignment itself but prevents permanent vision loss in the turned eye. Vision therapy, a structured program of eye exercises, can help improve coordination between the eyes in certain types of strabismus, particularly intermittent forms.
Surgery
Strabismus surgery adjusts the tension on the eye muscles, tightening or loosening them to bring the eyes into alignment. It’s the primary treatment for larger, constant deviations. Success rates generally fall between 70% and 80%, though some studies report rates above 90%. Smaller misalignment angles before surgery tend to predict better outcomes and a lower chance of needing a second procedure.
Recurrence is a real possibility. Up to half of patients with certain types of strabismus may see some return of the deviation within three years. Some people need a second surgery to fine-tune the alignment. The procedure is done under general anesthesia, typically as an outpatient surgery, and recovery involves a few weeks of redness and discomfort before the eyes settle into their new position.
Why Early Treatment Matters
In children, the window for preventing permanent vision loss is limited. The brain’s visual system is still developing through roughly age 7 to 9, and this is when suppression and amblyopia do the most damage. Treating strabismus early, whether with glasses, patching, or surgery, gives the brain the best chance to develop normal binocular vision and depth perception. Adults can still benefit significantly from treatment, especially for eliminating double vision and improving alignment, but restoring full depth perception is harder once the brain has spent years ignoring input from one eye.