The present invention provides a protective agent forretinal nerve or optic nerve which exerts its effect througha different mechanism from that of conventional therapeuticagents and can be taken for long periods. The present inventionis the protective agent for retinal nerve or optic nerve whichcomprises a compound with aldose reductase inhibiting activitysuch as the compound represented by the following generalformula as an active ingredient. A preferable compound thereofis (2S,4S)-6-fluoro-2',5'-dioxospiro[chroman-4,4'-imidazolidine]-2-carboxamide:(see formula 1)wherein X represents a halogen atom or a hydrogen atom, R1 andR2 independently represent a hydrogen atom or an optionallysubstituted C1 to C6 alkyl group, or R1 and R2, together witha nitrogen atom bound thereto, or optionally another nitrogenatom or an oxygen atom, are combined to form a 5- to 6-memberedheterocycle.
