Squint, also known as strabismus in medical term, is a condition where the eyes do not look in the same direction. Whilst one eye turns either inwards, outwards, upwards or downwards, the other eye looks forwards to focus on an object. It is one of the most prevalent ocular problems among children and affect about 5 in 100 children.
Usually squints develop before preschool age, mostly by the time a child is 3 years old. Sometimes, even babies have squint. It's normal for a newborn's eyes to wander or cross occasionally during the first few months of life. By the time a baby is 4 to 6 months old, the eyes usually straighten out. Also squints may develop in older children, or in adults.A child with a squint might develop visual loss called amblyopia (lazy eye) due to him ceasing to use the affected eye subconsciously. The condition may become permanent unless treated early in childhood.
Understanding the eye muscles
There are six muscles that control the eye in specific directions, namely lateral rectus (pulls the eye outwards), medial rectus (pulls the eye inwards), superior rectus (for upwards movements), inferior rectus (pulls the eye downwards), superior and inferior oblique (aid in stabilising the eye movements - especially for looking downwards and inwards, or for upward and outward movements respectively). When the eye muscles do not work together in a balanced way, a squint develops, causing an inability for the eye to move together correctly.
Type of Squints
Squints can be divided into several types based on :
An eye that turns upwards is called a hypertropia.
An eye that turns downwards is called a hypotropia
An eye that turns inwards is called an esotropia.
An eye that turns outwards is called an exotropia.
2. Whether the squint is present all the time (constant), or comes and goes (intermittent).
3. Whether the affected eye turns when the eyes are open and being used (manifest squint) or whether the eye turns only when it is covered or shut (latent squint) but looks fine when the eyes are open.
4. Whether the severity (angle) of the squint is the same in all directions or not:
A concomitant squint means that the angle (degree) of the squint is always the same in every direction that you look. That is, the two eyes move well, all the muscles are working but the two eyes are always out of alignment by the same amount, no matter which way you look.
An incomitant squint means that the angle of squint can vary. For example, when you look to the left, there may be no squint and the eyes are aligned. However, when you look to the right, one eye may not move as far and the eyes are then not aligned.
5. The age of onset. Most of the squints develop in the first three years of life. Some develop in older children and adults. Squints that develop in children usually have different causes to those that develop in adults.
The causes of squint (strabismus) in children
Congenital squints of unknown cause
Congenital squint means that the child is born with a squint, or it develops within the first six months of life. In most cases, the eye muscles are not balanced but the reason for this is not known.
In most cases one eye turns inward. This is called congenital esotropia (sometimes called infantile esotropia). This common type of squint tends to run in some families. However, many children with congenital esotropia have no other family members affected. In some cases, the eye turns outwards (congenital exotropia). Less commonly, a squint of unknown cause may result in an upward or downward turn of the eye.
Squint related to refractive errors
Refractive errors include: short sight (myopia), long sight (hypermetropia) and astigmatism. This leads to problems with focusing. These are all conditions that are due to poor focusing of light through the lens in the eye. An astigmatism is a vision problem where the surface of the eye (the cornea) or the lens, is more oval-shaped, rather than round. When the child with a refractive error tries to focus to see clearly, an eye may turn. This type of squint tends to develop in children who are 2 years or older, in particular in children with long sight. The squint is most commonly inward looking (an esotropia).
Most children with a squint have one of the above types of squint and are otherwise healthy. However, in some cases, a squint is one feature of a more generalised genetic or brain condition. Squints can occur in some children with cerebral palsy, Noonan's syndrome, Down's syndrome, hydrocephalus, brain injury or tumour, a rare type of eye cancer (retinoblastoma) and several other conditions.
How Vision Is Affected
The straight or straighter eye becomes dominant when the eyes are misaligned. The vision power (acuity) of the straight eye remains normal because the eye and its connection to the brain are functioning as they should. The misaligned or the weaker eye, however, does not focus properly and its connection to the brain is not formed correctly.
If strabismus is left untreated, the brain will eventually suppress or ignore the image of the weaker eye, resulting in amblyopia (or "lazy eye," when an eye is unable to focus on details) or permanent vision loss. Longstanding eye misalignment also might impair the development of depth perception (stereopsis) or the ability to see in 3D.
How is a squint (strabismus) diagnosed and assessed?
Most kids with strabismus do not complain of eye problems. Usually, the misalignment of the eyes is detected by the family member or teacher. Some squints are much less obvious than others. Another sign of squint is that your child might close one eye when looking at you, or turn his or her head on one side.
Some kids may complain of double vision (seeing two objects when there's only one in view) or have trouble seeing things in general. Younger children who are not yet able to verbalise their vision problems may squint frequently and turn or tilt their heads in an attempt to see more clearly.
However, it is quite common to notice a brief squint in children when they are tired or daydreaming. Babies sometimes cross their eyes - it is quite normal for this to happen occasionally, especially when they are tired. A squint seen in a newborn baby is likely to resolve if it is intermittent (comes and goes), reducing by 2 months of age and gone by 4 months of age. A baby with a constant fixed squint, or with an intermittent squint that is worsening from 2 months, should be referred for assessment.
If your child has any of these signs or symptoms, tell your doctor. If necessary, he or she can refer you to a pediatric ophthalmologist for proper evaluation and treatment. When detected early on, strabismus is curable through a variety of safe and effective treatment options. But it's important for kids to be treated early. Waiting too long or overlooking treatment completely can lead to permanent vision loss.
Dr Liew Yee Chian is a practicing medical officer in Sungai Buloh Hospital Ophthalmology Department. He was graduated from Udayana University Medical School, Bali in 2012，sponsored by Public Service Department (JPA). After completing his housemanship in Hospital Pakar Sultanah Fatimah, Muar (2012-2014), he started as a service medical officer in Sungai Buloh Hospital Neurosurgery Department from May 2014 till December 2015. Subsequently, he continued pursuing his medical career in Sungai Buloh Hospital Ophthalmology Department till now.