Strabismus is a condition where your eyes don’t line up to look at the same thing at the same time. One eye focuses on what you intend to see while the other points in a different direction, whether inward, outward, upward, or downward. It affects both children and adults, and when left untreated it can permanently change how the brain processes vision.
How Eye Alignment Works
Each eye is controlled by six small muscles that work together to point both eyes at the same target. Your brain coordinates these muscles so that each eye sends a nearly identical image, and the brain fuses those two images into a single picture with depth perception. This process, called binocular vision, is what lets you judge distances and see the world in three dimensions.
Strabismus disrupts this system. The misalignment can stem from problems with the eye muscles themselves, the nerves that control them, or the brain regions responsible for coordinating eye movement. In some cases, uncorrected vision problems like farsightedness force one eye to work harder to focus, pulling it out of alignment. The condition most often appears during the critical period of visual development in early childhood, but it can develop at any age.
Types of Strabismus
The direction the misaligned eye drifts determines the type:
- Esotropia: the eye turns inward, toward the nose. This is the most common form in young children.
- Exotropia: the eye turns outward, away from the nose.
- Hypertropia: the eye drifts upward.
- Hypotropia: the eye drifts downward.
Some people have a combination of horizontal and vertical misalignment. The turn can also be constant or intermittent. Intermittent strabismus, where the eyes drift apart only some of the time, generally means the brain still has some ability to fuse images from both eyes. That’s a better starting point for treatment.
What Causes It
In children, the most common risk factors include family history, premature birth, prenatal smoke exposure, and advanced maternal age. Many childhood cases don’t have a single identifiable cause. Instead, they result from a mix of genetic predisposition and subtle differences in how the eye muscles or brain pathways developed before or shortly after birth. A group of conditions called congenital cranial dysinnervation disorders involves abnormal wiring between the brain and the eye muscles, preventing full movement of one or both eyes.
Adults who develop strabismus later in life typically have a more specific trigger. Stroke, head trauma, and neurological conditions can damage the nerves controlling the eye muscles. Thyroid eye disease, an autoimmune condition most often linked to an overactive thyroid, causes inflammation and scarring in the eye muscles that restricts their movement. Lid retraction or a drooping eyelid in someone with new double vision is a strong clue that thyroid disease may be involved. Diabetes and high blood pressure can also damage the nerves supplying the eye muscles, leading to sudden misalignment.
What It Feels Like
The experience depends on when strabismus develops and how long it’s been present. Adults who develop it suddenly almost always notice double vision, because their brain is accustomed to fusing images from both eyes and can’t easily ignore the second image. This double vision is often disorienting and can cause headaches, difficulty reading, and trouble with balance.
Children and people who have had strabismus for a long time rarely see double. Instead, the brain learns to suppress the image from the misaligned eye, essentially ignoring it. This eliminates double vision but comes at a cost: depth perception is reduced, and the suppressed eye may develop amblyopia, sometimes called “lazy eye.” Amblyopia happens because the part of the brain responsible for processing that eye’s input never receives the stimulation it needs to develop properly. The vision loss isn’t in the eye itself; it’s in the brain. Even if the eye is structurally healthy, its visual sharpness is permanently diminished unless treated early.
How It’s Diagnosed
Strabismus is often visible, especially when the misalignment is large. But smaller deviations can be easy to miss, which is why routine eye screening matters. The American Association for Pediatric Ophthalmology and Strabismus recommends checking eye movement and alignment starting at birth, with referral for any infant who isn’t tracking objects well by three months. Screening continues through childhood and should be repeated every one to two years after age five.
One of the simplest tests is the Hirschberg test, also called the corneal light reflex test. A provider holds a small light in front of your face while you look at it, then checks where the reflection lands on each eye. If your eyes are aligned, the reflection appears in the same spot on both corneas. If the reflection is off-center on one eye, it suggests that eye is turned. A cover-uncover test takes it further: the provider covers one eye, then watches the other eye to see if it shifts to pick up focus. Any movement when an eye is covered or uncovered confirms misalignment.
Treatment for Children
Treating strabismus in children has two goals: straighten the eyes and protect vision in the weaker eye. If amblyopia has developed, the first step is usually patching the stronger eye. By covering the “good” eye for prescribed periods each day, you force the brain to rely on the weaker eye, stimulating the underdeveloped visual pathways. Blurring drops in the stronger eye can serve the same purpose. This treatment works best before age seven or eight, when the brain is still plastic enough to rewire those connections.
Glasses correct the misalignment in many children, particularly those whose eyes turn inward because of farsightedness. When the underlying vision problem is corrected, the eye muscles no longer need to overwork, and the eyes straighten. Vision therapy, a structured program of exercises using tools like prism lenses and specialized cards, can help strengthen the brain’s ability to coordinate both eyes. One common exercise uses “barrel cards,” where you hold a card against your nose and practice fusing colored images from both eyes into a single picture.
When glasses and therapy aren’t enough, surgery on the eye muscles can physically reposition them to improve alignment. The procedure adjusts the tension on the muscles, either tightening or loosening them so the eyes point in the same direction. In children, surgery is typically done under general anesthesia and recovery takes a few weeks, though soreness and redness around the eye often improve within days.
Treatment for Adults
Adults with strabismus have the same range of options: prism lenses, vision therapy, injections, and surgery. Prism lenses are built into glasses and bend light so that images land on the correct part of the retina in both eyes, reducing or eliminating double vision without changing eye position.
Botulinum toxin injections offer a less invasive alternative to surgery. Injected into an overactive eye muscle, the toxin temporarily paralyzes it, allowing the opposing muscle to pull the eye into better alignment. The effect typically lasts a few months, and some people need repeat injections. In one study of childhood esotropia treated with these injections, success rates reached 75% for smaller angles of misalignment using the lowest dose. The most common side effect is temporary drooping of the upper eyelid, which occurred in about 38% of patients at the lowest dose and more frequently at higher doses.
Surgery remains the most definitive option for large or persistent misalignment. Success rates in adults vary by type: about 80% for eyes that turn inward, 78% for vertical misalignment, and 57 to 58% for eyes that turn outward or those with combined horizontal and vertical deviation. Roughly 18% of adults who have strabismus surgery need a second operation, on average about 19 months after the first. For adults whose strabismus is caused by thyroid eye disease, surgeons typically wait until the inflammation has settled into a stable phase before operating, since the muscle restriction can change during the active disease.
Living With Strabismus
Beyond the visual effects, strabismus carries a significant social and psychological burden, particularly for children and teenagers. Visible eye misalignment can affect self-esteem, social interactions, and even job prospects in adulthood. Adults who have corrective surgery frequently report improvements in confidence and quality of life alongside the functional gains in vision.
Treatment at any age can improve alignment, reduce double vision, and in many cases restore some degree of binocular vision. The earlier treatment begins, the better the chances of developing normal depth perception. But even adults who were told as children that they were “too old” for treatment can benefit from modern approaches. The brain retains more capacity to adapt than was once believed, and correcting the alignment, whether through glasses, therapy, or surgery, consistently improves daily function and comfort.