Ophthalmology Terms

• Amblyopia - also known as “lazy eye.” Due to decreased function in one or both eyes.
• Anterior chamber - the fluid-filled space between the cornea and iris.
• Aqueous humor - the clear, watery fluid between the cornea and the front of the vitreous. The aqueous humor bathes and nourishes the lens and maintains pressure within the eye. Since the lens and cornea have no blood supply, the aqueous humor performs the blood’s job of carrying nutrients to those structures.
• Astigmatism - results from an irregularly-shaped or football-shaped cornea which causes light to refract ineffectively. Vision irregularities depend on the exact nature of the astigmatism.
• Cataract - a cloudy or opaque portion of the eye’s crystalline lens that can block vision.
• Choroid - the thin layer of major blood vessels that lies between the retina and sclera. The choroid supplies the retina with vital oxygen and nutrients. It thickens at the front of the eye to form the ciliary body.
• Ciliary body - the ring of muscle fibers that holds the lens of the eye. It also helps control intraocular pressure.
• Ciliary muscle - the smooth muscle portion of the ciliary body that is responsible for controlling the lens’ shape as it narrows or thickens to focus on images at different distances.
• Ciliary processes - the portion of the ciliary body that produces the eye’s aqueous humor.
• Cones - the receptor cells in the retina that detect color and fine detail.
• Conjunctiva - the transparent mucous membrane that lines the inner surfaces of the eyelids and covers the sclera, except at the cornea.
• Conjunctivitis - an inflammation or infection of the conjunctiva. Also known as “pink eye.”
• Cornea - the dome-shaped window of the eye that provides most of the eye’s optical power. Light enters through the cornea and is refracted by the cornea’s angle toward the back of the eye.
• Corneal transplantation - a surgical procedure to remove a diseased or scarred cornea and replace it with a healthy cornea from a deceased donor.
• Diabetic retinopathy - a condition associated with diabetes that causes retinal changes and hemorrhaging. More than 7 million of the 14 million Americans diagnosed with diabetes will experience some degree of diabetic retinopathy, which is the most common diabetic eye disease. Nearly all individuals with Type I (insulin dependent) diabetes will experience some retinal changes 15 years after diagnosis of diabetes. One-fourth of these will experience severe diabetic retinopathy. About 10% of individuals with Type II (non-insulin dependent) diabetes will experience severe diabetic retinopathy 15 years after diagnosis.
• Diopter - a unit of measurement—abbreviated as “D” on medical charts. It measures the degree to which light converges or diverges within the eye or through a lens, such as an eyeglass lens or contact lens.
• Drusen - white or yellowish deposits within the retina that commonly occur after age 60. Individuals with drusen are at increased risk of later developing abnormal blood vessels that leak and form scar tissue on the choroid.
• Emmetropia (the normal eye) - Light focuses precisely on the retina, and near and far objects are seen clearly.
• Gene therapy - a therapy to replace defective genes responsible for retinal degenerations, such as macular degeneration. This therapy currently is under investigation in the laboratories at the Emory Eye Center.
• Glaucoma - a group of diseases that result from increased intraocular pressure, which can result in damage to the optic nerve. A common cause of preventable vision loss.
• Hyperopia (farsightedness) - results when the eyeball is too short. Light rays hit the retina before they come into focus. Distant objects are clearer than near objects; however, even distant objects may appear blurry.
• Intracorneal ring - a tiny, transparent ring that can be inserted into the periphery of the cornea to change its shape and correct nearsightedness.
• Intraocular lens - a plastic implant that is used to replace the natural lens of the eye. Abbreviated as “IOL.”
• Iris - the ring of muscle fibers behind the cornea that determine eye color. The iris opens and closes the hole at its center—the pupil—to control the amount of light entering the eye.
• Keratoconus - a hereditary, degenerative condition that causes the cornea to thin and protrude into a cone-like shape.
• LASIK - laser in situ keratomileusis. A surgical procedure during which the top layer of the cornea is pulled back and the middle layer is sculpted to eliminate refractive errors such as nearsightedness, farsightedness and astigmatism. The top layer of the cornea is then replaced to serve as a protective flap.
• Lens - the almond-shaped, elastic structure within the eye that focuses images onto the retina. It is curved on both its front and back surfaces; the lens narrows or thickens to focus on images at different distances.
• Lensectomy - surgical removal of the lens. Often used to remove a cataract.
• Macula - the central portion of the retina that is responsible for the sharpest sight.
• Macular degeneration - the leading cause of blindness in individuals over age 60. Often called “rusting of the retina.” There are two main types, dry and wet. The dry or atrophic type is the most common—affecting nearly 70 percent of all cases—and results as the macula’s tissues age and break down, causing a gradual vision loss. The wet or exudative form of macular degeneration affects 15-20% of individuals with the disease and can significantly damage vision. It results when abnormal blood vessels form and leak fluid and blood in the choroid. The choroid’s blood vessels, combined with tissue, can form a scar-like membrane under the retina and block central vision.
• Melanoma - a malignant tumor arising from pigmented tissue. Melanoma can affect areas surrounding the eye, such as the eyelid or orbit, and the structures within the eye, such as the choroid and iris.
• Myopia (nearsightedness) - a condition in which the visual images come to a focus in front of the retina of the eye because of defects in the refractive media of the eye or because of abnormal length of the eyeball, resulting especially in defective vision of distant objects.
• Optic nerve - the largest nerve of the eye. Comprised of retinal nerve fibers (but no rods and cones), the optic nerve connects the retina to the primary visual cortex of the brain. Visual input from the retina travels along the nerve fibers of the optic nerve to the brain. The brain interprets images sent by the optic nerve of each eye, reverses the images, and integrates them into the one three-dimensional image that you see.
• Pars plana - the flattened back portion of the ciliary body.
• Posterior chamber - the space filled with aqueous humor that lies between the back of the iris and front surface of the vitreous.
• Presbyopia - results when the lens loses its elasticity due to aging. Reading glasses are needed to discern close-up objects and fine detail, such as print.
• Ptosis - a drooping of the upper eyelid.
• Retina - the innermost layer of blood vessels and nerves that serves as the “film” of the eye. The retina receives visual images and transmits signals to the optic nerve through its nerve endings, the rods and cones.
• Retinitis pigmentosa - A hereditary, progressive condition, RP causes abnormal pigmentation on the retina that can hinder vision. RP affects both eyes and can begin with a loss of night vision, progress to a loss of peripheral vision and then to “tunnel vision,” and finally result in blindness.
• Retinal cell transplantation - an experimental therapy currently being investigated in Emory Eye Center’s laboratories. The procedure involves transplanting healthy retina cells on the areas of the retina damaged by disease.
• Retinoblastoma - a malignant tumor of the retina that affects one in 20,000 children born in the U.S. If untreated, retinoblastoma can metastasize to other parts of the body, resulting in death.
• Retinopathy of prematurity - the most common blinding disease in premature infants. ROP is a disease of the retina.
• Rods - the receptor cells in the retina which are sensitive to varying degrees of light and help you see in dim light. The retina has about 150 million rods.
• Sclera - the tough outermost layer of the eye joining the cornea; the visible part is the white of the eye. The sclera has a transparent covering, the conjunctiva. The sclera helps maintain the eyeball’s shape, which is about one inch (25mm) in diameter.
• Strabismus - eye misalignment caused by an imbalance in the muscles holding the eyeball.
• Trabecular meshwork - the series of canals or tubes behind the iris that filters the aqueous humor and allows it to drain into the bloodstream.
• Uvea - the blood vessel-rich pigmented layers of the eye. It includes the iris, ciliary body and choroid. It contains the majority of the eye’s blood vessels.
• Uveitis - an inflammation of any of the structures of the uvea, including the iris, ciliary body or choroid.
• Vitrectomy - surgical removal of the vitreous, blood, and/or membranes from the eye.
• Vitreous or vitreous humor - the clear jelly that fills the eyeball behind the lens. It helps support the shape of the eye and transmits light to the retina.

With appreciation for guidance from the Dictionary of Eye Terminology, Second Edition, (1990), Barbara Cassin and Sheila A.B. Solomon, Melvin L. Rubin, M.D., Editor (Triad Publishing Company, Gainesville, Florida).