Science Daily (Sep. 17, 2007) — Children with amblyopia (commonly known as lazy eye) need only wear an eye patch for three to four hours a day for 12 weeks to improve vision, say researchers in a study recently published on the British Medical Journal website.
Patching for all waking hours for up to several years, which is often recommended, is almost certainly excessive, they argue.
Amblyopia results from a disturbance to the vision pathways between the eyes and the brain, which is often associated with blurred vision or crossed eyes (strabismus).
Studies have shown that occlusion therapy (patching) can improve vision, but results suggest that "maximal" doses (12 hours a day) are no more beneficial than "substantial" doses (six hours a day). Despite this, many doctors still prescribe large doses, above six hours a day.
So researchers at City University in London and McGill University in Montreal funded by Fight for Sight, London, set out to determine the amount of occlusion treatment required in children with amblyopia to achieve the best outcome.
The study involved 97 children aged 3-8 years with a confirmed diagnosis of amblyopia. All children had a full ophthalmic assessment and were instructed to wear glasses all the time for 18 weeks. On completion of this phase, 80 children who still met the study's definition of amblyopia were then told to wear a patch for either six or 12 hours a day.
Two electrodes were attached to the under surface of each patch to monitor the amount of occlusion each child actually received. Visual function was recorded every two weeks.
There was no significant difference in visual acuity between the two groups. However, the mean dose rates (hours a day with a patch) actually achieved were also not significantly different (4.2 in the six hour group and 6.2 in the 12 hour group).
Visual improvement was similar for those children who received 3-6 hours a day or 6-12 hours a day, but significantly worse for children who received less than three hours a day.
Children under 4 years of age required significantly less occlusion (under three hours a day) than older children to correct their vision.
This analysis suggests that achieving an initial dose rate of three to four hours a day should be a clinical priority, say the authors. The response depends on age, however, so for children under 4 years this could be reduced. Patching beyond 12 weeks did not confer additional benefit.
Eye patching can cause considerable distress for both the child and family, they add, so doctors should try to minimise the amounts necessary for the best expected outcome.
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