What causes eye misalignment? Discover the root causes, major risk factors, and distinct symptoms of accommodative esotropia and intermittent exotropia.
Strabismus Causes and Symptoms
Strabismus (crossed eyes) occurs when the eyes are not properly aligned with one another. To understand what triggers this condition, it helps to look at how the eyes and brain work together. Eye misalignment is typically caused by issues with the eye muscles, the nerves that carry signals to those muscles, or the brain's control center that coordinates eye movements. It can also develop following an eye injury or due to underlying systemic health conditions.
What Are the Main Causes of Strabismus?
The precise reason an individual develops strabismus often depends on their specific physical health, genetics, and neurological development. The root causes generally fall into four categories:
- Eye Muscle Weakness: An imbalance or poor control over the six muscles attached to each eye prevents them from moving in unison.
- Nerve Signaling Issues: Damage or dysfunction in the cranial nerves that control eye movement stops vital instructions from reaching the eye muscles.
- Brain Control Errors: The area of the brain responsible for blending the images from both eyes fails to coordinate eye movements properly.
- Trauma or Illness: Physical head injuries, strokes, or tumors can suddenly disrupt the delicate alignment network.
High-Risk Factors for Crossed Eyes
Anyone can develop strabismus, but certain factors significantly increase the likelihood of its development:
- Family History: Genetics play a powerful role. If you have a parent or sibling with strabismus, you are at a much higher risk of developing it yourself.
- Severe Refractive Errors: Individuals with significant, uncorrected farsightedness (hyperopia) frequently develop strabismus. The intense focusing effort required to keep distant and close objects clear forces the eyes to cross inward.
- Underlying Medical Conditions: Neurological and developmental disorders drastically elevate risk. Children with Down syndrome or cerebral palsy, and adults who have survived a stroke or traumatic head injury, experience much higher rates of strabismus.
Common Types of Strabismus & Their Specific Symptoms
While there are many distinct variations of eye misalignment, the two most common forms found in children and adults are accommodative esotropia and intermittent exotropia.
1. Accommodative Esotropia (Inward Turning)
This type typically develops because of uncorrected farsightedness. Because the eyes' focusing system is neurologically linked to the muscle system that directs where the eyes point, the extreme focusing strain forces one or both eyes to turn inward toward the nose.
Key Symptoms Include:
- Experiencing persistent double vision.
- A strong urge to close or cover one eye when doing close-up tasks or reading.
- Tilting or turning the head at unusual angles to try and force the eyes to focus together.
2. Intermittent Exotropia (Outward Turning)
This form stems from an inability to coordinate both eyes together as a team. The eyes exhibit a strong tendency to drift outward, pointing beyond the actual object being viewed.
Key Symptoms Include:
- Frequent headaches and noticeable eyestrain.
- Difficulty reading or losing your place on a page easily.
- A habit of squinting or closing one eye when looking at distant objects or when exposed to bright sunlight.
Frequently Asked Questions (FAQs)
What triggers sudden-onset strabismus in adults?
Sudden-onset strabismus in adults is usually a sign of an underlying medical disruption. It can be triggered by neurological events like a stroke, head trauma, or brain tumor, as well as systemic conditions like diabetes or thyroid eye disease that damage the nerves or muscles controlling eye movement.
How does uncorrected farsightedness cause eyes to cross?
The human eye naturally crosses slightly inward when focusing on things up close. If a child or adult has severe uncorrected farsightedness, their eyes must exert a massive, continuous focusing effort just to see clearly. This extreme over-focusing causes the eye muscles to over-converge, pulling the eyes inward into a cross-eyed position (accommodative esotropia).
Why do people with strabismus close one eye in bright sunlight?
People with intermittent exotropia (outward-turning eyes) frequently close one eye in bright sunlight. Bright outdoor light bleaches the retina and disrupts the brain's ability to blend images from both eyes, making it harder to control eye alignment. Closing one eye eliminates the resulting double vision and visual confusion.