A squint, known medically as strabismus, is a condition where the eyes don’t line up in the same direction. One or both eyes may turn inward, outward, upward, or downward, so they aren’t looking at the same object at the same time. It affects roughly 2% of children worldwide and can also develop in adults. While a squint is often noticeable to others, its effects go deeper than appearance: left untreated, it can permanently change how the brain processes vision.
Types of Squint
Squints are categorized by the direction the eye turns. When one eye drifts inward toward the nose, it’s called an esotropia, the classic “crossed eyes” look. When the eye turns outward toward the ear, it’s an exotropia, sometimes called “wall-eyed.” Less commonly, one eye may drift upward or downward, known as vertical squints.
There’s also an important distinction between a manifest squint and a latent squint. A manifest squint is visible all the time or at least some of the time. A latent squint only shows up when one eye is covered or when you’re very tired or unwell. Many people have a mild latent squint and never know it because their brain compensates automatically. It only becomes a problem if the eyes can no longer maintain alignment under normal conditions.
Some babies appear to have a squint when they actually don’t. This is called pseudostrabismus and usually happens because a wide, flat nasal bridge or prominent skin folds near the inner eye make it look like the eyes are crossed. As the child’s face grows, the illusion disappears. A proper eye examination can tell the difference.
What Causes a Squint
Each eye is controlled by six small muscles, and those muscles are directed by signals from the brain through three cranial nerves. A squint develops when this system breaks down at any level: the muscles, the nerves, or the brain’s control centers.
In children, the most common type is a concomitant squint, where the degree of misalignment stays roughly the same no matter which direction the child looks. These are generally caused by problems in the brain’s pathways for visual perception and eye movement control rather than a structural problem with the muscles themselves. Farsightedness is a particularly common trigger. When a farsighted child strains to focus, the extra effort causes the eyes to converge too much, pulling one eye inward.
In adults, squints more often result from specific injuries or diseases that damage the nerves or muscles directly. Stroke, head trauma, diabetes, thyroid eye disease, and neurological conditions can all disrupt the nerve signals that keep the eyes aligned. Orbital injuries and connective tissue disorders can physically change the muscles or their attachments. Because adults have a fully developed visual system, a new squint typically causes immediate double vision, which can be disorienting and debilitating.
Signs and Symptoms
The most obvious sign is eyes that visibly point in different directions. This may be constant or intermittent, appearing only when the person is tired, ill, or focusing at a certain distance. In young children, the misalignment can be subtle, and parents sometimes notice it only in photographs when the light reflects differently from each eye.
Beyond the visible misalignment, a squint disrupts binocular vision, the brain’s ability to merge the images from both eyes into a single three-dimensional picture. This means reduced depth perception, making it harder to judge distances. Adults who develop a squint usually experience double vision because their brain isn’t accustomed to receiving mismatched images. Children’s brains handle this differently: instead of seeing double, the brain often learns to ignore the image from the turned eye entirely. That suppression solves the double vision problem in the short term but creates a much bigger one.
The Link to Amblyopia
When a child’s brain consistently ignores one eye, that eye’s visual pathways stop developing normally. This leads to amblyopia, often called “lazy eye,” where one eye has significantly weaker vision even though the eye itself may be structurally healthy. If left untreated, amblyopia causes permanent vision loss in the affected eye.
The critical window for visual development is concentrated in the first seven years of life, with the earliest months being the most sensitive. Treatment started early, ideally in infancy, has the best chance of fully restoring vision. Children between ages 7 and 12 can still benefit from treatment, though results are more limited. After age 13, meaningful improvement becomes unlikely because the brain’s ability to rewire its visual pathways has largely closed. This is why early detection of a squint matters so much: it’s not just a cosmetic concern, it’s a time-sensitive threat to lifelong vision.
How a Squint Is Diagnosed
Eye specialists use a combination of tests to confirm a squint and measure its severity. The simplest is the corneal light reflex test, where a light is shone at the eyes and the specialist checks whether the reflection lands in the same position on both pupils. If one reflection is off-center, the eye is misaligned.
For more precise measurement, specialists use the cover test. You focus on a target while one eye is covered and uncovered. The specialist watches how the uncovered eye moves to pick up focus, which reveals both the direction and size of the deviation. Prisms, small wedge-shaped lenses, are placed in front of the eye during the test to quantify the angle of misalignment in units called prism diopters. Research shows the corneal light reflex test alone is substantially less accurate than the prism cover test, particularly for larger deviations where it tends to underestimate the true angle. This is why a thorough examination typically includes both methods.
Non-Surgical Treatments
Treatment depends on the type and cause of the squint, the patient’s age, and how severely vision is affected. Many childhood squints improve significantly with non-surgical approaches alone.
Corrective glasses are often the first step, especially when farsightedness is driving the misalignment. Properly prescribed lenses reduce the focusing effort that triggers excessive eye convergence, which can substantially reduce or even eliminate the inward turning. Studies show that corrective glasses also improve depth perception in children with refractive errors. Bifocal lenses are sometimes used when the squint is more pronounced during close-up tasks like reading.
Patching, or occlusion therapy, treats the amblyopia that accompanies many childhood squints. The stronger eye is covered for set periods each day, forcing the brain to use the weaker eye and strengthen its visual pathways. This doesn’t fix the alignment directly, but it protects against permanent vision loss in the turned eye.
Prism lenses are thin stick-on lenses applied to regular glasses. They bend light so that the images reaching each eye line up more closely, reducing double vision and helping the eye muscles work toward a new balance. Prisms are particularly useful for adults who aren’t candidates for surgery or who prefer a non-invasive option. Orthoptic exercises, guided by a specialist, train the brain and eye muscles to coordinate more effectively and can help with certain types of intermittent squints.
When Surgery Is Needed
If non-surgical treatments don’t achieve adequate alignment, surgery on the eye muscles is the next option. The procedure adjusts the tension of the muscles that control eye position. A surgeon may move a muscle further back on the eyeball to loosen its pull (recession), shorten a muscle by removing a section to tighten it (resection), or fold a muscle over itself to increase its tension (plication). Often, muscles on both eyes are adjusted in the same operation to achieve the best balance.
Surgery for horizontal squints (eyes turning inward or outward) has a reported success rate of 60% to 80%, with some studies achieving alignment in about 83% of patients. Smaller deviations tend to have better outcomes: one study found recurrence rates of 16% for smaller squints compared to 31% for larger ones. Some patients need a second procedure to fine-tune the alignment, particularly those with large-angle squints or dense amblyopia.
In children, early surgery can restore the conditions needed for binocular vision to develop, but it doesn’t automatically fix amblyopia. Patching and glasses are usually still necessary after the operation. In adults, surgery primarily aims to reduce double vision, improve eye alignment, and restore a more natural appearance. Recovery typically involves a few weeks of redness and discomfort, with full healing over one to two months.
Squint in Adults
Adults sometimes assume squint surgery is only for children, but treatment at any age can be worthwhile. An adult-onset squint caused by a nerve palsy may resolve on its own as the underlying condition heals, particularly after a mild stroke or temporary inflammation. In these cases, prism lenses can manage double vision during the waiting period.
When a squint persists, surgery remains effective in adults and can dramatically improve quality of life. Double vision from a squint makes driving, reading, and working at a computer difficult or impossible. Even for adults with a longstanding childhood squint who won’t gain binocular vision from surgery, correcting the alignment often has meaningful psychological and social benefits. The misperception that it’s “too late” prevents many adults from seeking treatment that could genuinely help them.