Ophthalmology is the branch of medicine which deals with the diseases of the eye and their treatment. The word ophthalmology comes from the Greek roots ophthalmos meaning eye and logos meaning word; 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. By convention the term ophthalmologist is more restricted and implies a medically trained specialist. Since ophthalmologists perform operations on eyes, they are generally categorized as surgeons.