Squint (Strabismus)
Jayesh Doctor
Squint (strabismus) - Patient Education
Normally, the two eyes move parallel to each other in all the directions of gaze.

Squint is a misalignment of the two eyes so that both eyes are not looking in the same direction. In other words, the two eyes don't look straight in the primary gaze. It is a common condition among children. It may also occur in adults.

At birth, the eyes don't move together. One eye moves differently from the other till the first few months. After that, the baby starts fixing the eyes on the light which is called light fixation and the eyes start moving together.

Under normal circumstances, when both the eyes have good vision and they are aligned properly, they focus on the same object. Each of the eyes sends picture! of the same object, viewed from a slightly different angle. These two images reach the brain, where they are fused to form a single three-dimensional picture with depth perception. This is known as binocular single vision.

Six muscles control the movement of each eye. Each of these muscle acts along with its counterpart in the other eye to keep both eyes aligned properly. A loss of co-ordination between the muscles of the two eyes leads to misalignment. This misalignment may be the same in all directions of gaze, or in some conditions the misalignment may be more in one direction of gaze.

Squint may be:
Paralytic Squint:
Means one of the muscle attached to the eyes is paralyzed and the eye affected may turn in/out/up/down depending on the muscle involved i.e. the eye movement is restricted in the direction of the action of the paralyzed muscle. This can be caused by direct trauma to the muscle as for e.g. injury during forceps delivery or any other injury. It may also be caused by certain nerve palsies, which in turn may be caused by peripheral neuritis or diseases of the CNS, e.g. meningitis, encephalitis etc. Treatment of paralytic squint depends on the cause and many a time paralytic squint may not be completely cured. In such cases, spectacles with prisms are prescribed.

Non-Paralytic Squint:
A loss of co-ordination between the muscles of the two eyes leads to misalignment. This misalignment may be the same in all direction of gaze, or in some conditions the misalignment may be more in one direction of gaze.

The squint is diagnosed by the ophthalmologist. He or she would do a few special tests (Cover - Uncover Tests) to confirm the squint, to try and find out the cause and to quantify the amount of derivation. In some cases, there may be a false appearance of squint due to broad nasal bridge in a child. An ophthalmologist will be able to differentiate between a true squint and false squint.

Refractive error like Hypermetropia (long sight) may lead to inward deviation of the eye (Convergent squint) and Myopia (short sight) may lead outward deviation of eye (Divergent squint). Therefore, it is important in all the cases of squint, especially in children, to have a thorough eye check-up to rule out any other cause of loss of vision. Convergent squint can be corrected by giving plus lenses. Divergent squint can be corrected by giving minus glasses.

When the eyes are not aligned properly, each of the eyes is focusing on a different object and sends signal to the brain. These two different images reaching the brain led to confusion and may have either of the two effects:

A child would ignore the image coming from the deviated eye, and thus sees only one image. But in the process, he loses the depth perception. This suppression of the image from the deviating eye results in poor development of vision in this eye, which is known as "amblyopia". It is important to treat the amblyopia before the surgery for squint. Occluding the good eye for prescribed number of hours/day treats it.

Vertical Squint:
Can be paralytic or nonparalytic. They are usually difficult to treat. Surgery may correct it or glasses with prism may have to be prescribed. Usually squint correction surgery is performed around the age of 5-6 years of age.

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