Patient Information

Eye leaflets

Orthoptics Department, Colchester Eye Centre
Colchester Primary Care Centre
Tel: 01206 487 100


Squint and Amblyopia


Squint is defined as a misalignment of the eyes. One eye points in a different direction to the other, this can be in, out, up, down or rotational.

Amblyopia (lazy vision) is defined as poorer vision in one or both eyes.

Normal vision is recorded as 0.00, 6 / 6 or 20 / 20.


Obstruction to development

If a child has any of the following obstructions to visual development during the critical period then they can develop amblyopia (lazy vision):

  • longsighted, short-sighted or astigmatism (a need for glasses)
  • squint
  • droopy upper eyelid
  • pathological eye condition (such as cataract)
  • trauma



For normal vision to develop there are several criteria that need to be met:

  • the eye must be anatomically normal with all associated brain connections
  • there must not be any physical obstructions to visual input
  • there must be a clear image with no blurring effect, so spectacles must be worn if needed
  • both eyes must be aligned and used together as a pair for 3D vision to develop.


Critical period

Visual development begins at birth and is usually completed by the age of approximately eight years. This whole time period is called the critical period of visual development. The earlier the treatment is started, the better the chance of a good result.



Amblyopia is the official name of lazy vision. It is the persistence of weak vision even after the above obstructions are removed. Vision involves not only the eye but the brain too. It is thought that the poor stimulation of sight during development can lead to under-development of the brain pathways responsible for vision.

If any of the above obstructions are corrected early enough it can be possible to prevent amblyopia from developing. However, this is not a hard and fast rule as every child is an individual.


3D vision

Normally, the two eyes coordinate together as a pair, enabling 3D vision. A squint prevents interaction of the eyes. If an adult develops a squint, they get double vision because up until then the eye has worked normally.

Children have a safety mechanism where they ignore or suppress the image from the squinting eye. Surgery can help correct the alignment of the eyes and in some cases this 3D vision is restored depending on the age of onset and type of squint.

Even though the eyes may look perfectly straight, and no squint is detectable, the eyes may not function as a pair and reduced vision can still be present, usually in the previously squinting eye.

Surgically aligning the eyes therefore does not necessarily improve the vision. Often squints are associated with a need for glasses. As this is a contributing factor reduced vision may still be present.



Vision is the priority. Any glasses needed are given. Patching treatment may be needed if the vision is reduced. Surgical alignment for cosmetic improvement can be considered later.


Additional information

Lazy Eye Treatment (Opens in a new window)



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