What drug is indicated for reducing pupil size in posterior lens luxation?

Latanoprost is an effective choice for reducing pupil size, particularly in cases of posterior lens luxation. This medication is a prostaglandin analog that specifically causes miosis, or constriction of the pupil, by stimulating the iris sphincter muscle. Latanoprost is often used in veterinary medicine to manage conditions like glaucoma and can help stabilize the position of the lens when it has luxated, as a smaller pupil reduces the risk of further displacement.

The other options do not effectively address the issue at hand. Atropine, for example, is a mydriatic agent that causes dilation of the pupil, which is counterproductive in this situation. Prednisone is a corticosteroid that might reduce inflammation but does not influence pupil size directly. Mannitol is an osmotic diuretic used primarily to reduce intraocular pressure in cases of glaucoma rather than managing pupil size or lens luxation. Therefore, latanoprost is the most suitable choice for this particular clinical scenario.