Eye Care Glossary


  • amblyopia: often referred to as "lazy eye"; a condition caused by a lack of normal sight development in one eye during early childhood. This is a common ailment which occurs in approximately 2-3% of the population.
  • anti-reflective coating: thin layers of material added to the surface of a lens that reduce the amount of light reflected by the lens surface which allows more light to reach the eyes, improving visual quality.
  • astigmatism: a condition caused by an irregularity in the shape of the cornea which prevents light from focusing correctly on the retina thereby causing blurred vision. Symptoms may include headaches, fatigue, eye strain, or blurred vision at certain or all distances.


  • bifocal: a lens that is designed with two different prescription areas to correct for both near and distance vision.
  • bridge: the part of a spectacle frame that extends across the nose.


  • cataract: refers to a clouding or decreased transparency of the lens in the eye. Cataracts may be present at birth (congenital cataracts) or occur due to the normal aging process, disease, or environmental factors.
  • color blindness: an inability to distinguish between certain colors such as red and green (most common form - colors would appear as yellow). This condition is an inherited trait that occurs almost exclusively in males, but the recessive gene that causes the condition is carried by the female.
  • cone: nerve cells of the retina (along with rods) that transmit impulses along the optic nerve to the brain. Cones provide color vision and respond best to bright light.
  • conjunctivitis: commonly referred to as "pinkeye"; an infection of the mucosal membrane that both covers the eye and lines the eyelid and is caused by bacterium, viruses, or allergies. Symptoms include redness, itching, and discharge. Treatment is often performed with antibiotics or cortisone. This infection was a major cause of blindness in infants prior to the use of silver nitrate eye drops for newborns.
  • cornea: transparent layers of cells and proteins that cover the front of the eye and serve to both control and focus light into the eye. Most common problems with visual acuity, including hyperopia (farsightedness), myopia (nearsightedness), and astigmatism, are due irregularities in the shape of the cornea.
  • corneal abrasion: a cut or scratch within the cornea. This may be caused by foreign objects such as dirt, sand, wood or metal shavings, dust, fingernails, etc. that come in contact with the surface of the eye. Firm rubbing of the eyes can also cause an abrasion.
  • corneal ulcer: an erosion or open sore in the outer layers of the cornea caused by infection, abrasion, foreign bodies, severe allergy, severe dryness of the eye, various types of inflammatory disorders, stress, and an impaired immune system. Symptoms include eye pain, redness, blurred vision, light sensitivity, increased tearing, or a white patch on the cornea.


  • diabetic retinopathy: leading cause of blindness among individuals of working age; caused by complications associated with diabetes in which blood vessels of the retina become damaged and leak causing retinal swelling and the formation of deposits (non-proliferative or background retinopathy). The condition becomes more serious when new, weaker vessels form on the surface of the retina that can bleed into the vitreous causing severe visual impairment (proliferative retinopathy).
  • diopter: unit of measurement that describes the refractive (light-bending) power of a lens and is used in prescriptions. A negative value indicates a correction for nearsightedness (myopia), while a positive value indicates a correction for farsightedness (hyperopia).



  • farsightedness: see hyperopia.
  • floaters: small clumps of cells or gel in the vitreous that appear as specks or clouds moving within the field of vision. These clumps or strands are caused by a thickening or shrinking of the vitreous gel within the eye which then pulls away from the back surface of the eye (posterior vitreous detachment).


  • glaucoma: a disease in which the optic nerve becomes damaged. This is most often caused by an elevated pressure inside the eye (intraocular pressure) due to the build up of a liquid substance called the aqueous humor. This condition is the leading cause of blindness among African-Americans.


  • high index: a term used to describe a type of spectacle lens that has a higher index of refraction than standard glass or plastic lenses. Because theses lenses are more dense than standard glass or plastic, light rays pass more quickly through the lens to the eye and do so with less material (i.e. thinner, lighter lenses).
  • hyperopia: farsightedness; vision of nearby objects is impaired, while distance objects remain in relative focus. Light is focused on a point that lies behind the retina.


  • iris: the muscular diaphragm that controls the size of the pupil. The iris itself is NOT responsible for eye color, but rather allows the pigmentation of the choroid (a layer beneath the sclera or white portion of the eye) to be visible.



  • keratoconus: a progressive thinning of the cornea which results in a cone-shaped bulge that causes blurry or distorted vision. This condition may result from heredity, injury, or certain eye or other diseases. Usually the cornea heals and regains stability without causing severe visual impairment, but in few instances the cornea will gradually deteriorate and require a corneal transplant.


  • LASIK: Laser-Assisted In Situ Keratomileusis; a type of refractive surgery in which a thin layer of corneal tissue is removed via laser to correct certain degrees of myopia.
  • lens: transparent structure within the eye that focuses light rays upon the retina.
  • macula: small area of the retina that contains specialized light-sensitive cells that provide detail and allow for performance of fine tasks and reading.
  • multifocal: term that describes a type of lens (spectacle or contact lens) that has more than one focal area such as bifocal, trifocal, or progressive ("no-line bifocal") lenses.
  • myopia: nearsightedness; close objects are in relative focus while distant objects are blurred. Light is focused on a point that lies in front of the retina.


  • nearsightedness: see myopia.


  • ocular hypertension: a condition of elevated pressure within the eye (intraocular pressure) that may lead to glaucoma.
  • ophthalmologist: a doctor of medicine (M.D.) or doctor of osteopathy (D.O.) who specializes in both the medical treatment and surgical care of the eyes and the visual system. Ophthalmologists must complete four or more years of medical school, one year of internship, and three or more years of specialized training and experience.
  • optician: state licensed professionals who interpret and fill a prescription from an optometrist or ophthalmologist for corrective eyewear. An optician is trained in the selection and fitting of eyeglasses and contacts (with special license). Qualifications for licensure include successful completion of a 2 year college program in optical science or a 2 year apprenticeship under a licensed optician or optometrist, followed by a state license examination. Opticians must also attend continuing education classes each year to maintain their license.
  • optometrist: doctors of optometry (O.D.) who specialize in the examination of the eyes and the visual system as well as the diagnosis and treatment of certain ocular diseases, injuries, and other health problems. An optometrist can prescribe many ophthalmic medications, but cannot perform surgery. They may, however, participate in pre-operative and post-operative care relating to eye surgery. Optometrists must complete four years of post-graduate optometry school.


  • photochromic lenses: spectacle lenses that undergo a chemical reaction when exposed to the ultraviolet (UV) wavelengths in sunlight. The reaction causes molecules within the lens to absorb light which causes them to darken.
  • polarized lenses: spectacle lenses that contain a polarizing filter that eliminates glare providing superior visual acuity and enhanced color perception while reducing eye strain and fatigue.
  • polycarbonate:
  • presbyopia: condition that arises when the lens in the eye becomes less flexible, making it difficult to bring close objects into focus and requiring special correction via bifocal or multifocal lenses or contacts. Often becoming noticeable by the age of 40-45, presbyopia is not a disease, but simply a natural part of the aging process.
  • progressive lenses: also referred to as "no-line bifocals"; multifocal lenses which provide visual correction for all distances. The different levels of correction are presented gradually over the lens. Typically, distance vision is corrected in the upper half of the lens, the middle area is for intermediate distances, and the lower part of the lens provides n increasing amounts of correction for close objects.
  • PRK: Photorefractive Keratectomy; a procedure in which a small section of the corneal surface is removed with a laser in order to modify its refractive properties and provide correction for problems with visual acuity.
  • pupil: the adjustable opening at the center of the iris that allows variable amounts of light into the eye. The pupil will expand or dilate in response to low light conditions in an attempt to bring more light into the eye and will reduce in size when intense light is present.


  • refractive surgery: a surgical procedure that corrects problems with visual acuity with the objective of reducing or eliminating the need for prescription glasses or contact lenses.
  • retina: a thin layer of light sensitive nerve tissue lining the interior of the eye that translates light waves into nerve impulses that are sent to the brain.
  • retinal detachment: occurs when the retina separates from the rear wall of the eye. Vision loss occurs at these detached areas.
  • retinitis pigmentosa: a genetically inherited condition in which rod cells degenerate causing impaired vision in low light conditions and may eventually lead to diminished peripheral perception.
  • RGP: Rigid Gas Permeable; a type of contact lens that is made of a permeable plastic that is custom made to the shape of the cornea and allows for oxygen to pass through the lens to the eye.
  • rods: light-sensitive cells located in the peripheral (side) areas of the retina. They are responsible for detecting movement, shape, light and dark. The visual picture provided by rods is in black and white.
  • RK: Radial Keratotomy; a surgical procedure in which several incisions are made in the cornea in a radial or spoke-like pattern in order to flatten the cornea and correct for myopia.


  • sclera: the outer layer of the eye that forms the visible white area of the eye and extends from the cornea in the front of the eye to the back of the eye where it meets and surrounds the optic nerve.
  • strabismus: "crossed eyes"; a condition in which the one or both of the eyes are misaligned caused by poor muscular control. The condition often occurs in children before 21 months of age but may develop as late as age 6. Treatments include corrective eyewear, visual therapy, or surgery.
  • sty: an inflammation of the eyelid near the eyelash caused by a blockage of a gland in the eyelid due to bacterial infection.


  • toric lenses: a lens used to correct astigmatism by providing two different optical powers at 90-degree angles to each other.
  • trifocal: a lens designed with three different focal areas. Often the top segment provides distance correction, a center segment corrects for intermediate distances, and the lower portion corrects for near objects and reading.
  • ultraviolet (UV): light rays that compose part of the invisible portion of the electromagnetic spectrum. Excess exposure to UV radiation can be harmful to eyes and skin resulting in sunburn, skin cancer, cataracts, etc.
  • UVA: a component of ultraviolet radiation that can pass through window glass and penetrate the layers of the skin. This light is most intense during early morning and afternoon hours and is responsible for tanning of the skin and wrinkles. Greater than 90% of UV radiation is composed of UVA.
  • UVB: a component of ultraviolet radiation that is most intense during midday. Unlike UVA, it cannot penetrate window glass, but is associated with sunburn.

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