Blurred vision or crossed eyes are the typical symptoms of amblyopia, caused by a disturbance in the pathway of vision between the eyes and the brain.
Researchers at City University in London and McGill University in Montreal asked 80 children aged three to eight with amblyopia to wear a patch for either six or 12 hours a day.
The patch was fitted with sensors that were wired to a data logger, which recorded how long the patch was actually worn.
However, the visual improvement between the two groups was the same.
Wearing the patch for less than three hours led to a much slower improvement across the two groups.
The exception were children aged under four, who corrected their sight quickly with just a few hours daily.
Patching beyond 12 weeks did not confer additional benefit.
As wearing a patch can be distressful for a child and burdensome for their parents, doctors can use these findings to minimise the "dosage," say the authors.