Learn what strabismus (crossed eyes) is, its 4 primary types, how it differs from a lazy eye, and why children do not simply outgrow it. Read our medical guide.
Understanding Strabismus (Crossed Eyes)
Strabismus is a common eye condition where both eyes do not look at the same place at the same time. It occurs when one eye turns inward, outward, upward, or downward while the other eye focuses straight ahead. This misalignment is usually caused by poor eye muscle control or a high degree of uncorrected farsightedness (hyperopia).
Six specialized muscles control the movement of each eye. Normally, the brain sends coordinated signals to these muscles so both eyes point at the exact same target. When these signals or muscles do not sync correctly, eye alignment is lost.
The misalignment can be constant or intermittent, often appearing only when a person is tired, ill, reading, or doing close-up work. While it most frequently develops in infants and young children by age three, older children and adults can also develop strabismus.
Strabismus vs. Amblyopia: What is the Difference?
Strabismus is frequently confused with amblyopia (lazy eye), but they are distinct conditions.
- Strabismus is a physical misalignment of the eyes (the eyes point in different directions).
- Amblyopia is a neurological reduction in vision in one eye because the brain has learned to ignore that eye's input.
The Connection: Constant, untreated strabismus in one eye is a leading cause of amblyopia. When the eyes are misaligned, the brain receives two different images, which initially causes double vision. To protect itself from confusion, the young brain learns to ignore the image from the misaligned eye. If left untreated, this can cause permanent vision loss in that eye.
Types and Classifications of Strabismus
Eye specialists classify strabismus based on the direction the eye turns, how often it happens, and whether it shifts between eyes.
1. Direction of the Eye Turn
- Esotropia: The eye turns inward toward the nose ("crossed eyes").
- Exotropia: The eye turns outward away from the nose ("wall eyes").
- Hypertropia: The eye turns upward.
- Hypotropia: The eye turns downward.
2. Frequency of the Turn
- Constant: The eye is misaligned all the time.
- Intermittent: The alignment is normal at times but shifts out of place occasionally.
3. Eye Involvement
- Unilateral: The exact same eye turns out of alignment every time.
- Alternating: The misalignment shifts back and forth; sometimes the right eye turns, and other times the left eye turns.
What is Pseudo-Strabismus (False Strabismus)?
Sometimes, a baby may look like they have crossed eyes when they are actually perfectly aligned. This is known as pseudo-strabismus.
This false appearance is usually caused by a wide bridge of the nose or extra folds of skin (epicanthal folds) that temporarily cover the inner white corners of the eyes, especially when the baby looks to the side. As the child's facial structure grows and changes, this illusion naturally disappears.
Important Safety Note: A parent cannot reliably tell the difference between true strabismus and pseudo-strabismus. Any infant older than four months whose eyes do not appear completely straight should be examined by an eye specialist. Children do not outgrow true strabismus, and delaying care can make the condition worse.
Frequently Asked Questions (FAQs)
What is the most common cause of strabismus?
Strabismus is typically caused by a failure of the eye muscles to work together in harmony, which is often linked to poor neurological control from the brain. It can also be triggered by severe uncorrected farsightedness (hyperopia), where the intense focusing effort causes the eyes to cross inward.
Can a child outgrow strabismus?
No. It is a dangerous misconception that children will naturally outgrow a crossed eye. Without professional medical intervention, true strabismus often worsens over time and can cause permanent vision problems, like amblyopia (lazy eye).
Can adults suddenly develop strabismus?
Yes, adults can develop strabismus. While it usually starts in childhood, adult-onset strabismus can happen due to medical issues such as stroke, diabetes, thyroid eye disease, head trauma, or neurological conditions affecting the eye muscles.
Is strabismus a permanent condition?
Strabismus is highly treatable and does not have to be permanent. Depending on the type and severity, treatment options include prescription eyeglasses, vision therapy, prism lenses, or eye muscle surgery. Early diagnosis provides the best treatment outcomes.