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Amblyopia

Amblyopia, or lazy eye, is a disorder of the eye. It is characterised by poor or blurry vision in an eye that is otherwise physically healthy and normal. The problem is caused by either no transmission or poor transmission of the visual image to the brain for a sustained period of dysfunction or disuse 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. more...

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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 affects 2-5% of the population. 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 develops abnormally. This has been confirmed in brain specimens.

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, most notably poor depth perception.

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).

Strabismic amblyopia

Strabismus, sometimes known as lazy eye, will result in normal vision in the fixating eye, but abnormal vision in the strabismic eye due to the brain discarding certain information. Strabismus usually develops into double vision (diplopia) in adulthood, 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, vision therapy, surgery or patching.

Refractive amblyopia

If anisometropia is present, refractive amblyopia may result. Anisometropia exists 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 are more susceptible to the development of amblyopia, which may be as severe as strabismic amblyopia. Despite its severity, refractive amblyopia is commonly missed by primary care physicians 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 prescription lenses. Vision therapy and/or eye patching can also be used to develop and/or improve visual abilities, binocular vision, depth perception, etc.

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Frequent amblyopia screening improves children's vision - Tips from Other Journals
From American Family Physician, 11/1/02 by Anne D. Walling

The long-established practices of early childhood screening for amblyopia and patching of the dominant eye are not supported by evidence of good clinical outcome. Williams and colleagues used a large longitudinal study of child development in southwest England to analyze the outcomes of screening and early intervention in children with amblyopia.

All children who were born in the region during a six-month period were eligible for the study. The 3,490 participating children received the usual early screening administered by family physicians and nurse practitioners and, later, screening for visual acuity by school nurses. Participants in the study were randomly allocated to normal amblyopia surveillance or intensive screening and intervention. Children in the intensive-screening group received age-appropriate visual testing and assessment by an orthoptist at eight, 12, 18, 25, 31, and 37 months of age. Children in the control group were assessed by an orthoptist at 37 months of age. All children who failed acuity or cover testing were referred to a hospital-based eye service.

At 7.5 years, data were available for 1,088 (54 percent) of the intensive-screening group and 826 (55 percent) of the control group. The prevalence of amblyopia in the intensive-screening group was 0.6 percent, significantly less than the 1.8 percent prevalence in the control group. Mean visual acuity in the amblyopic eye was significantly better in children treated in the intensive-screening group than in children in the control group who also had been treated for amblyopia. The proportion of children appropriately referred for hospital treatment before three years of age was significantly higher (48 percent) in the intensive-screening group than in the control group (13 percent). In multivariate analysis, maternal education was the only variable that was significantly associated with outcome.

The authors conclude that children who required treatment for amblyopia were four times more likely to remain amblyopic if they were screened only at 37 months of age. In addition, early treatment for amblyopia was more effective than later interventions.

EDITOR'S NOTE: The "inverse care law" strikes again! Families with more resources and comfort with the health care system benefited most from the services, even when treatment was free. Despite problems with follow-up, this study provides evidence that early detection and intervention for amblyopia improves vision in young children. The implications for their academic and social development are obvious. Our challenge is to find ways to ensure that all children are screened and treated, especially those from the most vulnerable families.--A.D.W.

COPYRIGHT 2002 American Academy of Family Physicians
COPYRIGHT 2002 Gale Group

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