An agent for the prevention, treatment and/or inhibition of progression of an ophthalmic disease and an agent for the protection of an optic nerve, each of which comprises (2R)-2-propyloctanoic acid or a salt or prodrug thereof in which an amount per dose is from 0.3 ng to 5000 mg. The agents are useful for an ophthalmic disease, such as glaucoma, cataract, retinal detachment, muscae volitantes, age-related macular degeneration, diabetic retinopathy, macular edema, myopia, asthenopia, dry eye, amaurosis fugax, choked disc, papillitis optica, retrobulbar neuritis, toxic amblyopia, optic atrophy, higher visual pathway lesion, internuclear opthalmoplegia, gaze palsy and ischemic optic neuropathy.