What Is A Squint? What Is Strabismus?
A squint, also known as strabismus is a condition in which the eyes do not align properly, one of them turns inwards, upwards, downwards, or outwards while the other one focuses at one spot. Typically, the extraocular muscles are not working in coordination, resulting in each eye unable to gaze at the same spot at the same time.
If both eyes are not completely aligned, binocular vision is not possible, making it harder for the person to appreciate depth perception.
Strabismus can also be caused by a disorder in the brain which cannot coordinate the eyes correctly.
According to the National Health Service (NHS), UK, squints affect approximately 5% of children and usually develop during their first 36 months of life (sometimes later). Squints are sometimes identified in infants a few days after they are born.
Four types of squints:
- The eye turns inwards - Esotropia (less common)
- The eye turns outwards - Exotropia (less common)
- The eye turns upwards - Hypertropia
- The eye turns downwards - Hypotropia
The earlier in life a squint can be identified and treated, the more effective that treatment is likely to be. A squint, if left untreated, can eventually develop into lazy eye (amblyopia), in which the brain starts ignoring input from one of the eyes. The brain ignores one of the eyes to avoid double vision.
If a child has poor vision in the squinting eye, wearing a patch over the other eye might help the squinting eye's proper development.
Sometimes a squint comes back later in adulthood, even though it had been successfully treated when the patient was a child. In such cases the adult may have double vision, because by that time the brain is trained to gather data from both eyes, it cannot ignore one of them.
According to Medilexicon's medical dictionary:
Strabismus is "A manifest lack of parallelism of the visual axes of the eyes."
What are the signs and symptoms of a squint (strabismus)?The sign of a squint is fairly obvious - one of the eyes does not look straight ahead, but veers. Some people may have minor squints that are less noticeable.
Infants (newborns) may go cross-eyed, especially if they are tired. This does not mean they have a squint. Concerned parents should check with their doctor.
If you notice that your child has one eye closed, or turns his/her head when looking at you, this could be a sign of double vision, and a squint is possible. Check with your doctor.
What are the causes of a squint (strabismus)?Strabismus can be congenital (you are born with it), it can run in families, it can be the result of an illness, long-sightedness, it can also be a sign that a cranial nerve has a lesion. The fact that it can sometimes run in families suggests a genetic link.
In the majority of cases, people are either born with strabismus or develop it during their first six months after birth.
The patient's eye might not be able to focus the light as it comes in through the lens - known as a refractive error. This can occur if the person has myopia (short-sightedness), hypermetropia (long-sightedeness), or astigmatism (the cornea is not curved properly). A refractive error will typically make the child turn the affected eye inwards in an attempt to get better focus. Strabismus caused by refractive errors tend to cause squints later on, usually when the child is at least two years' old.
Hydrocephalus, a condition in which too much CSF (cerebrospinal fluid) has built up in and around the brain, can cause squints to develop.
Some viral infections, such as measles can cause strabismus.
Noonan syndrome, and some other genetic conditions can cause squints
How is a squint diagnosed?In most developed nations as well as in many other parts of the world, children and babies have routine eye checks at specific points in their lives. In the UK a child is checked at birth, then again at 6 to 8 weeks, plus another routine check just before they start primary school.
The GP (general practitioner, primary care physician) or optician will refer the child to an ophthalmologist if strabismus is suspected. Eye drops will probably be used which dilate the pupils before the test is done.
The Hirschberg test, also known as the Hirschberg corneal reflex test is used to assess whether the patient has strabismus. 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.
Some people may suffer from more than one tropia at the same time.
What are the 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 - if the child is found to have hypermetropia (long-sightedness), they will be prescribed glasses which usually solve the squint.
Eye patch - this is worn over the good eye to get the other eye, the one with the squint, to work better.
Botulinum toxin injection (botox) - this is injected into a muscle on the surface of the eye. The doctor may recommend this treatment if no underlying cause can be identified, and if signs and symptoms come on suddenly. The injected muscle is weakened temporarily, which often helps the eyes to align properly.
The doctor may also prescribe eye drops, and get the patient to do specific eye exercises.
Surgey - 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 that connects to the eye to a new position - sometimes both eyes need to be operated on to get the right balance.