Eye Terms

Common terms -- symptoms, tests, treatments, surgery, diseases & conditions, anatomy -- eye doctors use. These definitions may help you understand them better.

Amblyopia: A condition that starts in childhood in which vision has not developed properly in one eye or the other. If amblyopia is left untreated, a child's vision will not develop correctly and as the brain matures, one eye will remain with poor vision.

Aqueous humor: The clear, watery fluid between the lens and the cornea.

Astigmatism: A condition in which blurred vision is caused by the cornea being shaped more like a football than spherical. Astigmatism may be compensated for through eyeglasses or contacts or can be corrected through refractive surgery.

Beta-blocker: A medication used in the treatment of glaucoma, beta-blocker eye drops help reduce the pressure within the eye by reducing the production of aqueous humor.

Carbonic anhydrase inhibitor: A type of medication used to treat glaucoma. Carbonic anhydrase inhibitors work by reducing the production of aqueous humor, thereby reducing pressure inside the eye.

Choroid: The layer of blood vessels between the retina and the sclera.

Choroiditis: A form of uveitis that causes an inflammation of the layer beneath the retina. It may also be caused by an infection such as tuberculosis.

Conjunctiva: A thin layer of tissue that lines the inside of the eyelids as well as the outer surfaces of the sclera.

Conjunctivitis: Inflammation of the conjunctiva also called pinkeye.

Cornea: The clear outer layer of the eye. It covers the iris.

Cryotherapy: A surgical procedure in which abnormal cells are destroyed by freezing them.

Cyclitis: A form of uveitis that causes inflammation of the middle portion of the eye and may affect the muscle that focuses the lens. Cyclitis may develop suddenly and last several months.

Dilation: Expansion.

Enucleation: A procedure in which the eye is removed.

Hyperopia: A condition in which a person has difficulty seeing objects up close, but objects further away are seen clearly. Hyperopia is commonly referred to as farsightedness.

Intraocular: Of or related to the inside of the eye.

Iris:The colored membrane of the eye, surrounding the pupil. The iris controls the amount of light entering the pupil by expanding and contracting.

Iritis: The most common form of uveitis, it affects the iris and is often associated with autoimmune disorders such as arthritis. Iritis may develop suddenly and may last up to eight weeks, even with treatment.

Legal blindness: Having visual acuity that, in both eyes, can not be corrected to better than 20/200 or has a visual field of 20 degrees or less (tunnel vision) remaining.

Low vision: A condition in which a person is either legally blind (visual acuity of less than 20/200 or tunnel vision) or visual acuity between 20/70 and 20/200 despite the use of conventional corrections such as prescription eyeglasses.

Macula: The central portion of the retina, a healthy macula is critical in maintaining sharp vision.

Macular edema: A swelling of the macula that can cause vision to become blurred or impaired. It is usually caused by an injury or disease.

Myopia: A condition in which a person has difficulty seeing objects in the distance. Myopia is commonly referred to as nearsightedness.

Nightblindness: A condition in which a person has impaired vision in dim or darkened conditions. Night blindness is commonly caused by a deficiency in vitamin A.

Nyctalopia: See night blindness.

Ocular: Of or relating to the eye.

Ophthalmologist: Ophthalmologists are doctors who specialize in the medical and surgical care of the eyes and visual system, and also the prevention of eye disease and injury. They can be either doctors of medicine (MD) or doctors of osteopathy (DO). As a qualified specialist, an ophthalmologist is qualified to deliver total eye care, meaning vision services, eye exams, medical and surgical eye care, diagnosis and treatment of disease, and visual complications that are caused by other conditions, like diabetes.

Ophthalmoscope: An instrument used to examine the retina. There are two types of ophthalmoscopes: direct and indirect. The direct version is used to examine the center of the retina, while the indirect is used when an exam of the entire retina is needed.

Optic nerve: The nerve that connects the eye to the brain. The optic nerve carries impulses of light from the retina to the brain, which then interprets the impulses as images.

Optometrist: A medical specialist trained to examine, diagnose, treat, and manage some diseases and disorders of the eye. Like ophthalmologists, optometrists are trained to examine the internal and external structure of the eyes to detect diseases such as glaucoma, retinal diseases, and cataracts. Optometrists do not perform surgery and are not trained to care for and manage all diseases and disorders of the eyes. The optometrist is trained to diagnose and treat vision conditions like nearsightedness, farsightedness, astigmatism, and presbyopia.

Peripheral vision: The region of sight where we see objects to the side, out of one's direct line of vision.

Photocoagulation: A surgical procedure in which a laser is used to stop bleeding blood vessels or to repair damaged tissue. Photocoagulation can also be used to help treat a tumor found in the eye.

Pinkeye: See conjunctivitis

Presbyopia: The loss of the eye's ability to change its focus to see objects that are near. Presbyopia is not a disease, but a part of the natural aging process of the eye that affects everybody at some point in life. It generally starts to appear around age 40 to 45.

Pupil: The round, dark, central opening of the eye through which light enters.

Refraction:The ability of the eye to bend light so that an image focuses directly on the retina.

Refractive error: A condition in which light bends incorrectly, causing an image to be out of focus. The most common refractive errors are astigmatism, farsightedness, and nearsightedness.

Retina: The thin layer of nerves that lines the back of the eye. The retina senses light and transmits light impulses to the optic nerve and then the brain.

Retinitis pigmentosa: Any of a number of inherited disorders in which there is a progressive loss of vision. In general, patients with this disorder first experience a loss of night vision, which is then followed by tunnel vision and eventually a loss of central vision.

Retinoblastoma: A malignant tumor that forms on the retina. Retinoblastoma most often affects children under the age of 5. It can occur in one or both eyes.

Sclera: The outer coat of the eyeball that forms the whites of a person's eyes.

Strabismus: A condition in which the eyes are misaligned and unable to point in the same direction at the same time. Crossed eyes is an example of strabismus.

Tunnel vision: A condition in which a person lacks any peripheral vision. Tunnel vision can be caused by any number of conditions including retinitis pigmentosa, untreated glaucoma, and stroke.

Visual acuity: How well a person sees.

Visual field: The entire range in which a person can see, including peripheral vision.

Vitrectomy: A procedure in which the vitreous humor is removed from the eyeball and replaced with a clear gel or liquid. Vitrectomies are done when scarring or blood in the vitreous is causing blockage of vision.

Vitreous humor: The clear gel-like substance found inside the center of the eyeball.