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).
The doctor must give you your prescription for glasses at the end of your eye exam. The doctor must give you your contact lens prescription when your fitting is complete. A fitting may require more than one appointment. If the doctor is ready to sell you contacts, the fitting is complete.