Glossary

• View movie of the anatomy of the eye

(Requires Flash Player - Download)

• Read text description

Accommodation: the ability of the eye to increase its focusing power. As an object is viewed closer up, greater focusing power is needed to continue to see it clearly.
Anterior Chamber: the fluid-filled space in the eye between the back surface of the cornea (endothelium) and the front of the iris.
Antibiotic: a medication to treat or prevent infection from bacteria.
Anti-inflammatory: a medication to reduce inflammation (the body's response to surgery, injury, irritation, or infection).
Astigmatism: a distortion of the image on the retina caused by irregularities in the refractive power of the cornea and/or lens.
Cataract: cloudiness of the natural lens inside the eye that can blur vision.
Cornea: the clear, transparent cover over the iris and pupil on the front part of the eye. The cornea is the first part of the eye that bends (or refracts) the light and provides most of the focusing power of the eye.
Corneal Edema: abnormal fluid build-up in the cornea that can cause haziness and swelling of the cornea and resulting blurred vision.
Corneal Transplant: surgical treatment where the patient's cloudy cornea is cut away and a clear cornea, donated by someone who has died, is sewn into its place.
Crystalline (Natural) Lens: the eyes natural lens that bends light (refracts) to provide some of the focusing power of the eye. The eye's natural lens is able to change shape allowing the eye to focus at different distances.
Diopter: unit of measurement of refractive error. A negative diopter prescription for glasses or contact lenses signifies an eye with nearsightedness and positive diopter prescription signifies an eye with farsightedness.
Double Vision: seeing two images of a single object instead of one.
Endothelial Cells: the cells that line the inner surface of the cornea in a single layer (endothelium). They are responsible for pumping fluid out of the cornea to keep it clear. These cells gradually decrease in number over a lifetime. They can die off faster than normal from damage during surgery or after surgery. If the number of endothelial cells becomes too low, your cornea becomes cloudy, you lose vision and may require a corneal transplant.
Endothelium: the innermost layer of cells lining the inner surface of the cornea.
Farsightedness (Hyperopia): the inability to see near objects as clearly as distant objects. The need for accommodation to see even distant objects clearly, because the focusing power of the eye is too weak when the eye is not accommodating. Light rays come to focus behind the retina instead of on the retina when the eye is not accommodating.
Glare: scatter from bright light that causes discomfort and can decrease vision and the ability to perform tasks like driving.
Glaucoma: a group of eye diseases characterized by pressure that is too high for the optic nerve (the nerve that sends the signal of images created by the eye to the brain) to withstand. Damage to the optic nerve from glaucoma results in loss of peripheral and then central vision. Glaucoma may be treated with medications or surgery to try to stop further damage to the optic nerve and further loss of vision.
Halos: hazy rings around lights.
Hyperopia: see farsightedness
Inflammation: the body's response to surgery, injury, irritation, infection, or some foreign substances, often associated with pain, heat, redness, swelling, and/or loss of function.
Informed Consent: the process of obtaining a patient's permission for a procedure after the patient and doctor have discussed the risks, benefits, and alternatives of the procedure and the patient understands them.
Informed Consent Document (Consent Form): a form listing the most common and worst possible risks of a procedure, the alternatives to the procedure, and the possible benefits of the procedure, which the patient signs to document their agreement to have the procedure at the end of the Informed Consent process.
Intraocular: inside the eye.
Intraocular Lens: a lens that is surgically implanted inside the eye.
Intraocular Pressure: the pressure of fluid inside the eye.
Iris: colored ring of tissue suspended behind the cornea and immediately in front of the lens separating the anterior chamber from the posterior chamber.
Iritis: inflammation of the front portion of the eye that can lead to scarring inside the eye and glaucoma.
Iridotomy: incision of the iris.
Laser Iridotomy: production of a small hole in the outer edge of the iris using a laser beam.
Myopia: see nearsightedness.
Nearsightedness (Myopia): the inability to see distant objects as clearly as near objects, because the focusing power of the eye is too strong. Light rays come to focus in front of the retina instead of on the retina.
Optic Nerve: the large nerve of the eye that carries visual signals from the retina to the brain to allow sight. Damage to the eye's optic nerve results in loss of vision or blindness. Once the optic nerve is permanently damaged, it cannot be repaired or replaced by a transplanted optic nerve.
Over Correction: the refractive error of the eye is corrected too much causing someone who is nearsighted to become farsighted or someone who is farsighted to become nearsighted.
Peripheral Iridectomy: surgical removal of part of the iris near its outer edge.
Phakic: with the natural lens of the eye; from the Greek word "phacos" meaning lens.
Phakic Lens: an intraocular lens that is implanted in the eye with the eye's natural lens still in place.
Posterior Chamber: the space in the eye between the back of the iris and the front of the vitreous (the jello-like substance that fills the space in the back central portion of the eyeball).
Pseudoexfoliation: abnormal deposits of white, flaky material seen on the structures in the front part of the eye that may be associated with cataracts and high pressure in the eye or glaucoma.
Pupil: the black hole in the center of the iris that changes size in response to changes in lighting. It gets larger in dim lighting conditions and smaller in bright lighting conditions.
Pupillary Block: blockage of the flow of fluid from the posterior chamber to the anterior chamber of the eye through the pupil. This can cause the pressure to build up inside the eye and can result in glaucoma.
Refraction: a test to determine the refractive power of the eye; also, the bending of light as it passes from one medium into another.
Refractive Error: imperfections in the focusing power of the eye, so that light rays are not brought into sharp focus on the retina, causing blurred vision that can usually be corrected with glasses or contact lenses. Nearsightedness (myopia), farsightedness (hyperopia), and astigmatism are refractive errors.
Refractive Power: the ability of an object, such as the eye, to bend light as light passes through it.
Refractive Surgery: general term referring to many different procedures to correct the refractive error of the eye.
Retina: a thin layer of sensory tissue that lines the inside wall of the back part of the eyeball. The retina acts like the film in a camera to capture images created by the focusing power of the cornea and the lens and transform them into electrical signals that are sent to the brain through the optic nerve.
Retinal Detachment: separation of the retina from its attachments to the back of the eyeball often resulting in loss of vision. Flashing lights, floating spots, and blank spots in vision can be symptoms of a retinal detachment.
Sclera: the white, protective outer layer of the eyeball that is continuous with the cornea in the front of the eye.
Shallow Anterior Chamber: narrowness of the space between the cornea and the iris.
Under Correction: the refractive error of the eye is not corrected enough leaving someone who is nearsighted still nearsighted or someone who is farsighted still farsighted to a certain degree.
Uveitis: general term for inflammation of the eye. Inflammation can be in the anterior (iritis), intermediate, and/or posterior portion of the eye.
Visual Acuity: the sharpness of vision; the measurement of the eye's ability to distinguish object details and shape.

Last Updated:

horizonal rule

Center for Devices and Radiological Health / CDRH