Eye disorders are treated by ophthalmologists or optometrists. Ophthalmologists are physicians and surgeons who specialize in the diagnosis and treatment of eye diseases. Optometrists are not physicians but have a doctor of optometry degree and do eye examinations, prescribe corrective lenses and prescribe drugs for certain types of eye disorders. Opticians are technicians who can fit eyeglasses and contact lenses using prescriptions provided by an ophthalmologist or optometrist. Opticians do not diagnose or treat eye diseases.
Each part of the eye has a unique function. Light enters the eye through the cornea, the clear, curved layer in front of the iris and pupil. After passing through the cornea, light travels through the pupil (the black dot in the middle of the eye). The pupil is actually an opening in the middle of the iris—the circular, colored area of the eye. Muscles that attach to the iris open and close the pupil to control the amount of light that enters the eye. Behind the iris sits the lens. By changing its shape, the lens focuses light onto the retina, a layer of tissue at the back of the eye. The retina contains the cells that sense light (photoreceptors). Each photoreceptor converts light into an electrical signal that is transmitted to the brain through a bundle of nerve fibers called the optic nerve.