Optometrists diagnose, manage and treat conditions and diseases of the human eye and visual system. During examinations, they diagnose problems or impairments, prescribe corrective lenses, and provide treatment. They prescribe eyeglasses, contact lenses and vision therapy. They also treat patients before and after surgery. In some states, optometrists may be allowed to prescribe medication to treat disease. Optometrists use instruments, eye drops and observation to determine the health of the patient’s eyes.