A squint ( Strabismus/Crossed eyes) is misalignment of eyes, wherein one eye appears straight and other eye may turn inwards, outwards, upwards or downwards.
Why do people get squint?
We have 6 muscles in each eye (2 Horizontal,2 Vertical and 2 Oblique muscles). These muscles known as extraocular muscles are attached to outer surface of eye and their balanced and coordinated movement keeps eye in straight gaze and aligned in all directions of gaze. When due to any cause, this coordination is lost, then both eyes can’t gaze at same spot simultaneously leading to crossed eyes.
If both eyes are not completely aligned, binocular vision is impaired leading to loss of depth perception (Stereopsis).
Types of squint:
There are four types of squints:
- The eye turns inwards - Esotropia
- The eye turns outwards - Exotropia
- The eye turns upwards - Hypertropia
- The eye turns downwards - Hypotropia
People can also have persistent or intermittent squints.
Symptoms of a squint (strabismus)
- Crossed eye/Deviated eye: The main symptom.
- Abnormal head posture : Sometimes children adopt abnormal head posture to avoid squint and to keep eyes straight
Causes of a squint (strabismus)
- Strabismus can be congenital : (you are born with it)
- Familial : it can run in families
- Long-standing illness or viral infections like measles
- Neurological cause like cranial nerve palsy, hydrocephalus etc.
- Uncorrected Refractive error like Myopia (short sightedness), Hypermetropia (Long sightedness) or astigmatism. Strabismus caused by refractive errors tend to cause squints later on, usually when the child is at least two years' old.
How is a squint diagnosed?
Strabismus can be diagnosed during an eye examination. It is recommended that all children have their vision checked by their pediatrician, family doctor or ophthalmologist on or before their fourth birthday.
Hirschberg corneal reflex test is simple test to evaluate squint . The ophthalmologist shines a light in the child's eye and observes where the light reflects off the corneas. In a person with well-aligned eyes, the light goes to the center of both corneas. If it does not, the tester can determine whether the patient has exotropia, hypertropia, esotropia or hypotropia depending on location of corneal reflex.
Prism Bar Cover test is the best test to evaluate squint. It tells not only the type of squint but also amount of squint.
Treatment options for a squint (strabismus)
A diagnosed squint needs prompt treatment, otherwise there is a serious risk of complications, such as amblyopia (lazy eye).
The younger the patient is, the more effective treatment is likely to be.
Glasses – Refractive error of each patient is evaluated by cycloplegic refraction and glasses are prescribed if necessary.In case of accommodative refractive esotropia, glasses corrects squint and so no further treatment is required in these patients
Eye patch – These are recommended if patients presents with complication of squint (amblyopia/lazy eye). This is worn over the good eye to get the other eye, the one with the squint, to work better and thus improve vision in squinting eye
Botulinum toxin injection (botox) - This is injected into a muscle on the surface of the eye. The injected muscle is weakened temporarily, which often helps the eyes to align properly.
Surgery - surgery is only used when other treatments have not been effective. Surgery can restore binocular vision, as well as realign the eyes. The surgeon moves the muscle to a new position - sometimes both eyes need to be operated on to get the right balance.
Whom to consult?
Squint specialist (Paediatric Ophthalmologists) are better trained to evaluate and treat these patients. Consult local Paediatric ophthalmologists in case of any doubt about crossed eyes