The present invention discloses a method of treating an ophthalmic infection by administering to a vertebrate inflicted with the ophthalmic infection an ophthalmologically effective amount of an antimicrobial peptide which is derived from alpha-melanocyte-stimulating hormone (.alpha.-MSH) and biologically functional equivalents thereof. Specifically, the antimicrobial peptides derived from alpha-melanocyte-stimulating hormone (.alpha.-MSH) include .alpha.-MSH (1 13) which is SYSMEHFRWGKPV, .alpha.-MSH (4 10) which is MEHFRWG, .alpha.-MSH (6 13) which is HFRWGKPV, .alpha.-MSH (11 13) which is KPV, and a KPV dimer. The ophthalmic infection can be caused by a microorganism which include a bacteria, a fungi or a virus. The vertebrate includes a bird and a mammal. The antimicrobial peptide has anti-bacterial, antifungal, and antiviral property and therefore can be administered at the onset of the ophthalmic infection before the microorganism causing the infection is determined as well as thereafter.