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.
The test found that, on average, the six-hour group wore the patch for 4.2 hours a day, while the 12-hour group wore it for 6.2 hours.
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.