Description
This article is from the Vision and Eye
Care FAQ, by grants@research.canon.com.au (Grant Sayer) with
numerous contributions by others.
6.1 Strabismus (Turned Eye)
A squint or strabismus is a failure of the two eyes to look at the same
object thereby preventing binocular vision. Human binocular vision develops
during the first few years of life. Interruption to the motor, sensory or
central components, for example nerve or muscle defect, can lead to sensory
or central defect. Causes of many squints are not fully understood although
the majority are either a hereditary factor or a responsible defect.
Such factors causing squints include;
+ ocular abnormalities that prevent good central vision,
eg congenital cataract.
+ paresis of one of the eye's muscle
+ brain damage, eg cerebral palsy
+ large refractive errors, eg accommodative esotropia
Refractive errors are an important causative factor to strabismus since it
can prevent clear vision - impeding development of the sensory mechanism,
and affecting the normal relationship between accommodation and convergence.
When the eye's require vision at a near distance there both a movement of the
two eyes (convergence) and change in focus (accommodation).
A child that is hypermetropic (long sighted) has to accommodate more than is
normally required for distance and near vision. Because of the linkage
between accommodation and convergence the excess accommodation causes an
excess convergence of the two eyes. The result, in a young child whose
visual system is still developing is what is called a convergent squint.
When binocular vision is disturbed double vision results. Young infants are
able to suppress one of the images to one eye to remove the double vision
that occurs at the onset of strabismus. The effect of the suppression of
the image causes the vision in the "squinting" eye to fail to develop
normally. This is called AMBLYOPIA. There are other visual abnormalities
that can develop as a result of squint.
The treatment for squint depends on the cause. Some essential treatments
include:
+ search for ocular defects
+ refraction and glasses to remove any refractive errors
+ patching or occlusion of the eyes to prevent amblyopia
+ surgical adjustments to the muscles of the eye.
These treatments aim to remove amblyopia, restore binocular vision and if
necessary cosmetic corrections to the appearance of the turned eye.
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