The present invention aims to find a novel pharmaceutical use of omidenepag, esters thereof, or salts thereof. The present inventors have made intensive studies to find a novel pharmaceutical use of omidenepag, an ester thereof, or a salt thereof, and have found as a result that omidenepag, an ester thereof, or a salt thereof significantly dilates retinal blood vessels, and significantly increases blood flow. Therefore, omidenepag, an ester thereof, or a salt thereof is expected to protect retinal nerve cells and be useful for prevention and/or treatment of ophthalmic diseases involving retinal nerve cell disorder.