The sign of a squint is fairly obvious from an early age. One of the eyes does not look straight ahead. A minor squint may be less noticeable.

• Infants and newborns may go cross-eyed, especially if they are tired. This does not mean that they have a squint. Parents can check with their doctor.

• If a child has one eye closed, or turns their head when looking at you, this could be a sign of double vision , and a possible squint. It is a good idea to see a doctor.

• Strabismus is normally either present at birth or it develops in the first 6 months after birth.

• Untreated, it can lead to amblyopia , or “lazy eye,” in which the brain starts ignoring input from one of the eyes.

• The brain ignores one of the eyes to avoid double vision.

• If there is poor vision in the affected eye, a child may benefit from wearing a patch over the other eye to encourage the vision to develop.

• Sometimes a squint that was treated successfully in childhood returns later in adulthood.

• If the eye cannot focus the light as it comes in through the lens, this is known as a refractive error.

Other problems that can lead to strabismus include:

• Myopia, or short-sightedness

• Hypermetropia, or long-sightedness

• Astigmatism, where the cornea is not curved properly

A refractive error tends to make the affected eye turn inward, in an attempt to get better focus.

Strabismus that results from refractive errors tends to emerge later on, usually around the age of 2 years or older.

• Children and babies should have routine eye checks as they develop. The American Optometric Association recommends starting eye tests at 9 months, or earlier if the child has a constant eye turn.

• If there are signs of strabismus, the physician or optician will refer the child to an ophthalmologist.

• The ophthalmologist will probably use eye drops that dilate the pupils before the test is done.

• The Hirschberg test, or Hirschberg corneal reflex test, is used to assess whether the patient has strabismus.

• The ophthalmologist shines a light in the eye and observes where the light reflects from the corneas.

• If the eyes are well-aligned, the light will go to the center of both corneas. If it does not, the test can show whether the patient has exotropia, hypertropia, esotropia or hypotropia.

• Some people may have more than one tropia at the same time.

Prompt treatment reduces the risk of complications, such as amblyopia, or lazy eye. The younger the patient is, the more effective treatment is likely to be.

• Glasses: If hypermetropia, or long-sightedness, is causing the squint, glasses can usually correct it.

• Eye patch: Worn over the good eye, a patch can get the other eye, the one with the squint, to work better.

• Botulinum toxin injection, or 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 appear suddenly. The botox temporarily weakens the injected muscle, and this can help the eyes to align properly.

• Eye drops and eye exercises may help.