Abnormal, harmful, or undesirable effect on an organism that causes anatomical or functional damage, irreversible physical changes, or increases the susceptibility to other biological, chemical, or environmental stresses.
Optometrists can prescribe glasses, contact lenses, eye exercises, vision aids and therapy, and (in some states) oral and topical medications to treat certain eye diseases. Ophthalmologists are doctors of the eye. They have graduated from medical school and are licensed to practice medicine, so their credentials are either doctor of medicine (MD) or doctor of osteopathy (DO).
An ophthalmologist is a medical doctor (MD) or osteopathic doctor (DO) who specializes in eye and vision care. Ophthalmologists perform eye exams, diagnose and treat disease, prescribe medication and perform eye surgery. They also write prescriptions for eyeglasses and contact lenses.