Search

The Online Encyclopedia and Dictionary

 
     
 

Encyclopedia

Dictionary

Quotes

   
 

Amblyopia

Amblyopia or lazy eye is a disorder of the eyes. It is characterised by poor or blurry vision that is not correctable with glasses in an eye that is otherwise physically healthy and normal. The problem is due to either no transmission or poor transmission of the visual image to the brain for a sustained period during early childhood. The condition will only arise at this young age because most of the visual system's development in humans is complete and "locked in" by a few years of age. Amblyopia normally only affects one eye, but it is possible to be amblyopic in both eyes if both are similarly deprived of a good, clear visual image.

Amblyopia is relatively common; it affects 2-5% of the population. Treatment is most useful if started before age 5, and seldom useful if started after age 10. If it is detected early enough, it may be corrected by occluding (covering) the stronger eye for periods of time to force the weak eye to develop good vision. In actuality, Amblyopia is a developmental problem in the brain, not an organic problem in the eye. The part of the brain corresponding to the visual system from the affected eye is not stimulated properly and will, therefore, develop abnormally. This has been confirmed in brain specimens. This treatment rarely works for adults, since the visual system is fully developed before adolescence. However, recent research has shown that some therapy can improve visual acuity slightly in adult amblyopes.

Many children who have amblyopia, especially those who are only mildly amblyopic, are not even aware they have the condition until tested at older ages, since the vision in their stronger eye is normal. However, people who have severe amblyopia may experience associated vision disorder s, most notably poor depth perception.

Contents

Types

Amblyopia can be caused by deprivation of vision early in life, or by strabismus (misaligned eyes), vision obstructing disorders and anisometropia (different degrees of myopia or hyperopia in each eye). Since strabismus is a common cause of amblyopia, it is sometimes also referred to as "lazy eye."

Strabismic amblyopia

Strabismus (misaligned eyes) will result in normal vision in the fixating eye, but abnormal vision in the strabismic eye due to the brain discarding its information. Strabismus in an adult usually causes double vision (diplopia), since the two eyes are not fixated on the same object. Children's brains, however, are more plastic, and therefore can more easily adapt by ignoring images from one of the eyes, getting rid of the double vision. This plastic response of the brain, however, interrupts the brain's normal development, resulting in the amblyopia.

Strabismic amblyopia is best treated by treating the strabismus through the use of prescription glasses, surgery or patching.

Refractive amblyopia

If anisometropia is present, refractive amblyopia may result. Anisometropia is when there is a difference in the refraction between the two eyes. The eye with less refractive error provides the brain with a clearer image, and is favoured by the brain. Those with this condition then become more susceptible to the development of amblyopia, which may be as severe as strabismic amblyopia. Despite its severity, refractive amblyopia is usually missed by doctors because of its less dramatic appearance and lack of obvious physical manifestation, such as with strabismus.

Refractive amblyopia is diagnosed when there is a wide disparity in visual acuity between the two eyes. Refractive amblyopia is treated by correcting the refractive error early, with or without eye patching.

Form deprivation and Occlusion amblyopia

Form deprivation amblyopia (Amblyopia ex anopsia) results when the ocular media is opaque, such as is the case with cataracts or corneal scar ring. These opacities prevent adequate sensory input from reaching the eye, and therefore disrupt visual development. If not treated in a timely fashion, amblyopia may persist even after the cause of the opacity is removed. Sometimes, drooping of the eyelid (ptosis) or some other problem causes the upper eyelid to physically occlude a child's vision, which may cause amblyopia quickly.

One should also be weary of creating this type of amblyopia in a 'good' eye when treating for amblyopia in the other eye – so-called reverse amblyopia.

This type of amblyopia is treated by removing the opacity as soon as possible.


Last updated: 02-16-2005 09:22:25
Last updated: 05-06-2005 01:27:49