Amblyopia

26/07/2014 by admin | Ophthalmology

Definition: is caused by either no transmission or poor transmission of the visual stimulation through the optic nerve to the brain for a sustained period of dysfunction or during early childhood thus resulting in poor or dim vision

Classification / type of disease:

Strabismic amblyopia: amblyopia caused by excessive strabismus

  • Abnormal vision in abnormal eye
  • If adult onset of strabismus = diplopia
  • Onset of strabismus in infants = more neuroplastic and therefore able to compensate – but interruption of brains normal function = amblyopia
  • Tx: glasses, and/or encouraging use of the amblyopic eye with an eyepatch over the dominant eye or pharmacologic penalization of it.

Refractive or anisometropic amblyopia

  • Refractive amblyopia may result from anisometropia (unequal refractive error between the two eyes).
  • The eye which provides the brain with a clearer image typically becomes the dominant eye.
  • Tx: correcting the refractive error early with prescription lenses and patching or penalizing the good eye.

Form-deprivation and occlusion amblyopia

  • Form-deprivation amblyopia (Amblyopia ex anopsia) results when the ocular media become opaque. These opacities prevent adequate visual input from reaching the eye, and therefore disrupt 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.
  • Occlusion amblyopia may be a complication of a hemangioma that blocks some or all of the eye.

 

Epidemiology

Presenting symptoms / signs:poor depth perception, poor spatial acuity, low sensitivity to contrast and some “higher-level” deficits to vision such as reduced sensitivity to motion. Also problems of binocular vision such as limited stereoscopic depth perception 

Diagnostic investigations: 

Aetiology: caused by either no transmission or poor transmission of the visual stimulation through the optic nerve to the brain for a sustained period of dysfunction or during early childhood thus resulting in poor or dim vision (= congenital cataracts, by strabismus, anisometropia [different degrees of myopia or hypermetropia in each eye], or by a significant amount of astigmatism in one or both eyes). Often unilateral.

Pathophysiology: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 develops abnormally.

 

Transmission

Treatment / management: 

  • Treatment of strabismic or anisometropic amblyopia consists of correcting the optical deficit (wearing the necessary spectacle prescritption) and often forcing use of the amblyopic eye, either by patching the good eye, or by instilling topical atropine in the eye with better vision.
  • Treatment of individuals age 9 through adult is possible through applied perceptual learning.
  • Form deprivation amblyopia is treated by removing the opacity as soon as possible followed by patching or penalizing the good eye to encourage use of the amblyopic eye. The earlier treatment is initiated, the easier and faster the treatment is and the less psychologically damaging. There is also a greater chance of achieving 20/20 vision if treatment is initiated as early as possible

 

Prognosis:Although the best outcome is achieved if treatment is started before age 5, research has shown that children older than age 10 and some adults can show improvement in the affected eye. Adolescents aged 13 to 17 showed improvement as well, albeit in smaller amounts than younger children.

Repetitive transcranial magnetic stimulation may temporarily improve contrast sensitivity and spatial resolution in the affected eye of amblyopic adults.

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