1. A method for treating a disease associated with damage to a retinal neuronal cell selected from the group consisting of abnormal visual field, retinal vascular occlusion, diabetic retinopathy, ischemic optic neuropathy, macular degeneration, retinitis pigmentosa and Leber's disease comprising administering to a patient in need thereof a pharmaceutically effective amount of a compound represented by the following formula (1) or a salt thereof: wherein the ring X represents a benzene ring or a pyridine ring; R 1 and R 2 are the same or different and represent a hydrogen atom or an alkyl group or R 1 and R 2 are joined together to form a cycloalkane ring; R 3 represents a hydroxy group, an alkoxy group, an aryloxy group, a cycloalkyl group, an alkylamino group, an arylamino group, a nitro group, a cyano group or a monocyclic heterocycle; and a cyclic moiety of the benzene ring, the pyridine ring, the cycloalkane ring, the aryloxy group, the cycloalkyl group, the arylamino group or the monocyclic heterocycle are unsubstituted or substituted with one or more substituents selected from the group consisting of a halogen atom, an alkoxy group and an alkyl group; and an alkyl moiety of the alkyl group, the alkoxy group or the alkylamino group are unsubstituted or substituted with one or more substituents selected from the group consisting of a halogen atom and an alkoxy group.