The word ophthalmology comes from the Greek roots ὀφθαλμός, ophthalmos, i.e., "eye" and -λoγία, -logia, i.e., "study of, discourse";[4][5] ophthalmology literally means "the science of eyes". As a discipline, it applies to animal eyes also, since the differences from human practice are surprisingly minor and are related mainly to differences in anatomy or prevalence, not differences in disease processes.[citation needed]