Ophthalmology is a term used to describe the medical and surgical care of the eye. It mainly handles the eyebrows, eyelids, orbit, lacrimal system, optic nerve, eye muscles and nerves connecting to the visual cortex. Eye disorders commonly affect the young and the aged, with the middle-aged affected by diseases like thyroid eye disease and ophthalmic trauma. Most of these disorders require the intervention of an ophthalmologist. Since the eye consists of several parts, there are different sub-specialties of ophthalmology such as pediatrics ophthalmology and strabismus, external eye disease including contact lenses, cornea and refractive surgery (cataract), glaucoma, and vitreoretinal surgery.