Glossary
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Accommodation
The ability of the eye to change its focus from distant to near objects; process achieved by the lens changing its shape. The lens in the eye is an elastic structure that changes shape in order to focus things near or far onto the retina. Optically, the greater the curvature of the lens, the greater its refractive power. To bring close objects into focus on the retina the lens must have a greater refractive power than in its resting state. This is accomplished via contraction of the ciliary muscles that hold the lens in place. When these muscle fibers contract, the lens, via its elasticity, springs into a more convex shape allowing a focused image of near objects. This is an energy requiring process since muscular effort is necessary, and therefore can be tiring.
Anterior Chamber
This front chamber of the three found in the eyeball is found between the cornea and the iris.
Aqueous Humor, Aqueous Fluid (A-kwe-us)
Clear, watery fluid that flows between and nourishes the lens and the cornea; secreted by the ciliary processes. This fluid fills the anterior and posterior chambers. It is made by cells of the ciliary body and circulates from the posterior chamber, over the lens to the anterior chamber and exits via the Canal of Schlemm. It is similar to plasma but contains very little protein.
Astigmatism (uh-STIG-muh-tizm)
A condition in which the surface of the cornea is not spherical; causes a blurred image to be received at the retina.
Binocular Vision
The blending of the separate images seen by each eye into a single image; allows images to be seen with depth.
Blind Spot
(1) A small area of the retina where the optic nerve enters the eye; occurs normally in all eyes. (2) Any gap in the visual field corresponding to an area of the retina where no visual cells are present; associated with eye disease.
Central Retinal Artery
Blood vessel that carries blood into eye; supplies nutrition to the retina.
Central Retinal Vein
Blood vessel that carries blood from the retina.
Central Vision
See Visual Acuity.
Certified Ophthalmic Personnel
These individuals, such as ophthalmic assistants, ophthalmic technicians and ophthalmic medical technologists, are qualified to assist the ophthalmologist in a variety of procedures, from history taking and basic tonometry to visual field testing and ophthalmic photography, depending on the level of certification. Certification in the subspecialty areas of Ophthalmic Surgical Assisting and Assisting in Low Vision are also available. The Joint Commission on Allied Health Personnel in Ophthalmology is the certifying agency.
Certified Ophthalmic Registered Nurses
A registered nurse who has a specialized body of knowledge, skills and experience. Ophthalmic nurses perform ophthalmic examinations, patient assessments based on human responses to ophthalmic diseases, triage, as well as teach patients about their ophthalmic conditions and prevention, assist in eye surgeries and provide emotional support to patients and their families. Ophthalmic registered nurses work in operating rooms, ambulatory clinics, private offices and hospitals. The goal of ophthalmic nursing is to assist patients in preserving and maximizing the vision that they have, prevent disabling eye disease through education, promote independence, and enhance the patient's quality of life. Eligibility for certification (CRNO) requires two years of practice in ophthalmology before taking the written examination.
Certified Orthoptists
An allied health professional in ophthalmology who works in an adjunctive capacity with an ophthalmologist in the diagnostic and therapeutic assessment of children and adults with strabismus, amblyopia, diplopia and disturbances of binocular function. Expert in the visual assessment of nonverbal patients and in the performance of diagnostic tests used to evaluate visual function; the orthoptist may also be skilled in refraction, visual field testing, electrophysiologic testing, contact lens evaluation and low vision assessment.
Choroid (KOR-oyd)
This is the vascular layer of the eye. A layer filled with blood vessels that nourishes the retina; part of the uvea.
Ciliary Body
This is an expansion of the choroid at the front of the eye at the level of the lens. The lens is attached to the ciliary body, which has smooth muscle within it. Contraction of this smooth muscle changes the shape of the lens and allows the eye to focus on objects. Part of the ciliary body is specialized to make aqueous humor.
Ciliary Muscles
The muscles that relax the zonules to enable the lens to change shape in order to focus.
Ciliary Processes
The extensions or projections of the ciliary body that secrete aqueous humor.
Cones, Cone Cells
One type of specialized light-sensitive cells (photoreceptors) in the retina that provide sharp central vision and color vision. Also see RODS.
Conjunctiva (KAHN-junk-TY-vuh)
The thin, moist tissue (membrane) that lines the inner surfaces of the eyelids and the outer surface of the sclera.
Contrast Sensitivity
The ability to perceive differences between an object and its background.
Cornea (KOR-nee-uh)
Transparent, colorless anterior making up one sixth of the covering of the eyeball. The cornea consists of 5 layers; the outer layer consisting of epithelium composed of 5-6 layers of cells that turnover every 7 days or so. This layer and the internal endothelium are responsible for keeping the cornea transparent. They do this by keeping the middle layers relatively dehydrated, which keeps the parallel collagen fibers present there from being opaque. The cornea contains no blood vessels and gets its nutrients from those in the anterior chamber fluid and surrounding vessels.
Dilation
A process by which the pupil is temporarily enlarged with special eye drops (mydriatic); allows the eye care specialist to better view the inside of the eye.
Drusen
Tiny yellow or white deposits in the retina or optic nerve head.
Fluorescein Angiography (FLOR-uh-seen an-jee-AHG-ruh-fee)
A test to examine blood vessels in the retina, choroids and iris. A special dye is injected into a vein in the arm and pictures are taken as the dye passes through blood vessels in the eye.
Fovea (FOH-vee-uh)
This specialized area of the retina is for the most acute vision. When a person is actively focusing or attending to an object the eyes are moved so that the image is focused on the fovea. It is thinner, containing only the cones necessary for detection of sharp images. The cones in this area are long and thin, resembling rods, so that they can be closely packed. Blood vessels are absent as well. Each foveal cone is directly connected to a neuron in the optic nerve.
Fundus
The interior lining of the eyeball, including the retina, optic disc, and macula; portion of the inner eye that can be seen during an eye examination by looking through the pupil.
Hyperopia (hy-pur-OH-pee-uh)
Farsightedness; ability to see distant objects more clearly than close objects; may be corrected with glasses or contact lenses.
Intraocular Pressure (IOP)
Pressure of the fluid inside the eye; normal IOP varies among individuals.
Iris
Another expansion of the choroid that partially covers the lens formed by pigment cells, fibroblasts, blood vessels and contractile pigment cells. The pigment found in the iris prevents light from entering the eye except through the pupil. The melanocytes (pigmented cells) are responsible for the color of the eyes. If there is little pigment in the cells the light reflected from the choroid at the back of the eye will make the iris appear blue. As the amount of pigment increases the iris appears greenish-blue, gray or brown.
Lacrimal Gland (LAK-rih-mul)
The small almond-shaped structure that produces tears; located just above the outer corner of the eye.
Legal Blindness
In the U.S., (1) visual acuity of 20/200 or worse in the better eye with corrective lenses (20/200 means that a person must be at 20 feet from an eye chart to see what a person with normal vision can see at 200 feet) or (2) visual field restricted to 20 degrees diameter or less (tunnel vision) in the better eye. NOTE: These criteria are used to determine eligibility for government disability benefits and do not necessarily indicate a person's ability to function.
Lens
This biconvex structure is very elastic, at least in the young. With age the lens looses its elasticity and therefore the ability to focus on near objects decreases. The center of the lens is formed by elongated cells (fibers) that have lost all organelles and are filled with special proteins called crystallins. These fibers are replaced throughout life but the regeneration slows down with age. Mature cataracts occur when these fibers accumulate pigment granules so that they are less transparent.
Low Vision
Visual loss that cannot be corrected with eyeglasses or contact lenses and interferes with daily living activities.
Macula (MAK-yoo-luh)
The small, sensitive area of the central retina; provides vision for fine work and reading.
Myopia (my-OH-pee-uh)
Nearsightedness; ability to see close objects more clearly than distant objects; may be corrected with glasses or contact lenses.
Ophthalmic Registered Nurses
See Certified Ophthalmic Registered Nurses.
Ophthalmologists
An ophthalmologist is a physician (doctor of medicine or doctor of osteopathy) who specializes in the comprehensive care of the eyes and visual system in the prevention of eye disease and injury. The ophthalmologist has completed four or more years of college premedical education, four or more years of medical school, one year of internship, and three or more years of specialized medical and surgical training and experience in eye care. The ophthalmologist is a physician who is qualified by lengthy medical education, training and experience to diagnose, treat and manage all eye and visual system problems, and is licensed by a state regulatory board to practice medicine and surgery. The ophthalmologist is the medically trained specialist who can deliver total eye care: primary, secondary and tertiary care services (i.e., vision services, contact lenses, eye examinations, medical eye care and surgical eye care), and diagnose general diseases of the body.
Ophthalmoscope
After the eyes are dilated, this tool provides the eye care professional with a wider view of the retina.
Optic Cup
The white, cup-like area in the center of the optic disc.
Optic Disc/Optic Nerve Head
The circular area (disc) where the optic nerve connects to the retina.
Optic Nerve
The bundle of over one million nerve fibers that carry visual messages from the retina to the brain.
Opticians
Opticians are professionals in the field of designing, finishing, fitting and dispensing of eyeglasses and contact lenses, based on an eye doctor's prescription. The optician may also dispense colored and specialty lenses for particular needs as well as low-vision aids and artificial eyes.
Optometric Technician
A paraoptometric who is prepared for widely diversified job duties through academic and clinical experience. Technicians work directly with optometrists in the areas of patient examination and treatment, including contact lenses, low vision, vision therapy and optical dispensing and office management. The optometric technician may have completed a college program in optometric technology that is a minimum of one academic year in length, or career ladder to the position by successfully completing the Optometric Technician Registry Examination. A registered optometric technician will have the Opt. T., R. designation.
Optometrists
The optometrist is a healthcare professional trained and state licensed to provide primary eye care services. These services include: comprehensive eye health and vision examinations; diagnosis and treatment of eye diseases and vision disorders; the detection of general health problems; the prescribing of glasses, contact lenses, low vision rehabilitation, vision therapy and medications; the performing of certain surgical procedures; and the counseling of patients regarding their surgical alternatives and vision needs as related to their occupations, avocations and lifestyle. The optometrist has completed pre-professional undergraduate education in a college or university and four years of professional education at a college of optometry, leading to the doctor of optometry (O.D.) degree. Some optometrists complete a residency.
Orbit
The frontal, maxilla, zygomatic, sphenoid, ethmoid, lacrimal and palatine bones form this cone-shaped cavity in the skull. These bones are thin and are often subject to fractures. The eye occupies the front portion on the cavity with the rest being filled with fat, nerves, blood vessels, muscle and the lacrimal (tear) gland.
Orthoptists
Paraoptometric
Professional who works under the direct supervision of a licensed doctor of optometry, collects patient data, administers routine yet technical tests of the patient's visual capabilities and assists in office management. The paraoptometric may assist the optometrist in providing primary patient care examination and treatment services, including contact lenses, low vision, vision therapy and optical dispensing and office management. State laws may limit, restrict or otherwise affect the duties that may be performed by the paraoptometric.
A paraoptometric is primarily involved in front office procedures, optical dispensing and contact lens patient education. The optometric assistant may be trained on the job or may have completed a formal education program that is less than one academic year in length, and successful completed the National Optometric Assistant Registry Examination. A registered optometric assistant will be designed by Opt. A., R.
Posterior Chamber
This chamber occupies space between the iris and the lens.
Peripheral Vision (per-IF-ur-al)
Side vision; ability to see objects and movement outside of the direct line of vision.
Phoroptor
Tool that measures the prescription for corrective lenses.
Posterior Chamber
The space between the back of the iris and the front face of the vitreous; filled with aqueous fluid.
Presbyopia (prez-bee-OH-pee-uh)
The gradual loss of the eye's ability to change focus (accommodation) for seeing near objects caused by the lens becoming less elastic; associated with aging; occurs in almost all people over age 45.
Pupil
Round opening in the iris that allows light to pass through. Pupil size changes based on the amount of light present. More light causes the pupil to contract while the pupil widens in the dark to collect as much light as possible.
Refraction
A test to determine the best eyeglasses or contact lenses to correct a refractive error (myopia, hyperopia, or astigmatism).
Retina (RET-in-nuh)
This photosensitive part of the eye lies between the vitreous body and the choroid layer at the back of the eyeball and is a complex network of photosensitive cells and various types of neurons. Light that reaches the retina must travel through several layers of transparent neurons at the front of the retina before reaching the photosensitive rods and cones. The photosensitive part of rods and cones is housed in extensions of the cells that look just like their names. The rods are responsible for black and white vision while the cones detect color. The neurons within the retina act to integrate the visual signals received by the rods and cones and transfer the information to the optic nerve.
Retinal Pigment Epithelium (RPE) (ep-ih-THEE-lee-um)
This layer lying between the retina and choroid, contains melanocytes that make for its characteristic black color. This pigment layer nourishes the retinal cells and allows the inside of the eye to absorb stray rays of light like the black paint inside a camera or within a dark room.
Rods, Rod Cells
One type of specialized light-sensitive cells (photoreceptors) in the retina that provide side vision and the ability to see objects in dim light (night vision). Also see Cones.
Schlemm’s Canal
This canal drains fluid from the anterior chamber. Obstruction of this canal leads to an increased intraocular pressure, which can damage the retina. This condition is also called glaucoma.
Slit Lamp
A slit lamp, with its high magnification, allows the eye care professional to examine the front of the eye.
Sclera (SKLEH-ruh)
The tough, white, outer layer (coat) of the eyeball; along with the cornea, it protects the entire eyeball.
Tonometer
A tool that measures pressure inside the eye and is one of several tests necessary to detect glaucoma.
Tonometry
The standard to determine the fluid pressure inside the eye (intraocular pressure).
Trabecular Meshwork (truh-BEC-yoo-lur)
The spongy, mesh-like tissue near the front of the eye that allows the aqueous fluid (humor) to flow to Schlemm's canal and then out of the eye through ocular veins.
Uvea, Uveal Tract (YOO-vee-uh)
The middle coat of the eyeball, consisting of the choroid in the back of the eye and the ciliary body and iris in the front of the eye.
Visual Acuity
The ability to distinguish details and shapes of objects; also called central vision.
Visual Field
The entire area that can be seen when the eye is forward, including peripheral vision.
Vitreous (VIT-ree-us)
The transparent, colorless mass of gel that lies behind lens and in front of retina.
Vitreous Space
The chamber that occupies the space behind the lens to the retina. It is filled with a gelatinous substance called the vitreous body.
Zonules (ZAHN-yoolz)
The fibers that keep the lens suspended in position and enable it to change shape during accommodation.
