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Commonly used


The definitions to some commonly used terms in Behavioural Optometry, as well as words we may be using to discuss you or your child's vision problems:

Accommodation (Acc)

  • the process by which the eye changes optical power to maintain a clear image or focus on an object as its distance varies. Accommodation acts like the “zooming in” mechanism of the eye.

  • The accommodation reflex is a reflex action of the eye, in response to focusing on a near object, then looking at distant object (and vice versa), comprising coordinated changes in binocular co-ordination, lens shape and pupil size.



  • the simultaneous inward movement of both eyes toward each other, usually in an effort to maintain single binocular vision when viewing an object. The “cross-eyed” appearance is one of excessive convergence..

Convergence Insufficiency

  • occurs when your eyes don't work together while you're trying to focus on a nearby object. When you read or look at a close object, your eyes need to turn inward together (converge) to focus. This gives you binocular vision, enabling you to see a single image.


  • the simultaneous outward movement of both eyes away from each other, usually in an effort to maintain single binocular vision when viewing an object.

Eye movement control (EMC)

  • refers to the voluntary or involuntary movement of the eyes, helping in acquiring, fixating and tracking visual stimuli. This control is critical for efficient ball sports and reading.

Spatial Awareness

  • the thinking concept of left/right position of yourself and others in the environment. It is an organised knowledge of objects in relation to oneself in that given space.

Visual Acuity

  • the measurement used to specify ones range of clear vision at different distances.

Accommodation/Convergence Dysfunction

  • describes a breakdown or underdevelopment in the relationship of the eyes working together at focusing and alignment.

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