This report reviews studies on the use of H 2 in the ophthalmological field. In retinal diseases, particularly in a retinal ischemia-reperfusion injury, effects of H 2 are remarkable in reducing retinal tissue damage. H 2 treatment of corneal damage caused by alkali or UVB suppressed scar formation. The most unique application of H 2 in the ophthalmological field appears to be its use in phacoemulsification cataract surgery. Ultrasound oscillation produces ·OH through the cavitation phenomenon in the anterior chamber of the eye, which induces oxidative insults in the corneal endothelium. Phacoemulsification using H 2 dissolved in the irrigation solution significantly suppressed the corneal endothelial damage. The effect of H 2 was direct and clear, as H2 instantly scavenges ·OH produced by ultrasound oscillation in the anterior chamber, thereby suppressing oxidative insults during the phacoemulsification procedure.