Four to six hours, depending on each person......and also on the drops being administered.
Dilating drops can have two effects: they can make the pupil larger and they can paralyse the near-distance focusing muscle (ciliary muscle). That is why strong light is more uncomfortable and it is harder to read under the effects of these drops.
When maximum dilation of the pupil is not required, we use tropicamide eye drops as sight is then regained in less than 3 hours in most cases. Cycloplegic eye drops (cyclopentolate) are stronger and have a longer-lasting dilating effect.
For children, we use other longer-lasting drops, which generally last for 12 hours. The effects of atropine eye drops may take 1-2 days to wear off.