Causes of Squint

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The brain mechanisms that control the full ability to fuse the images from the two eyes into one (binocular vision) develop during infancy and early childhood. Squint can occur when the devlopment is disrupted by stress on the eye.

The most important cause of squint is a focusing error in which the lens system of the eye is not strong enough to bring the image to focus on the retina (hypermetropia). This forces muscles around the lens to contract strongly to try to bring the image into focus. Because of reflex brain action, the affected eye turns inwards.

A squint causes double vision. To overcome this, the brain rejects the signals from the affected eye, and only the image from the normal eye is seen, even though the squinting eye itself can detect light normally.

From that moment on, visual development stops in the squinting eye. Without treatment, a severe and permanent loss of vision develops (see Amblyopia) . By the age of eight the whole system has firmed up. It is not possible to treat amblyopia after this age. The earlier amblyopia is treated, the easier it is to correct.

Squint occurring for the first time in adult life almost always causes double vision and requires urgent investigation. It may be a sign of a problem with the brain or nervous system, such as a stroke, diabetic nerve damage, or disease of the eye-moving muscles or their nerves.