A preventing or treating agent for glaucoma or ocular hypertension is provided. This drug has a strong action of reducing intraocularpressure such that the intraocular pressure can be reduced even from the normal intraocular pressure. More specifically, a prophylactic or therapeutic agent for glaucoma, a preventing or treating agent for ocular hypertension, and eye drops comprising (S)-(-)-1-(4-fluoro-5-isoquinolinesulfonyl)-2-methyl homopiperazine or its salt and phosphoric acid or its salt are provided.本發明係提供一種強效之降低眼壓作用，且即使對正常眼壓而言亦具有充分之降低眼壓作用之綠內障預防或治療劑。本發明之綠內障預防或治療劑、高眼壓症預防或治療劑、滴眼劑含有(S)-(-)-1-(4-氟-5-異喹啉磺醯基)-2-甲基升哌或其鹽、以及磷酸或其鹽。
