Final answer:
The most common osmotic diuretic used in ophthalmic surgery is mannitol, which is an indigestible sugar that promotes water loss by osmosis. It is administered to reduce brain swelling after head injury.
Step-by-step explanation:
The most common osmotic diuretic used in ophthalmic surgery is mannitol. Osmotic diuretics promote water loss by osmosis, and mannitol is an indigestible sugar that is often administered to reduce brain swelling after head injury. It works by attracting water and reducing the volume of fluid in the brain, leading to diuresis.