20/20 vision: Normal, perfect vision as measured on a Snellen letter chart. The number is a ratio in which the top number indicates the ‘distance at which the test is given’ over the number to indicate the ’distance at which a normal eye can read the letter’. Therefore vision of 20/20 indicates a test given at 20 feet/a normal eye can see the letter at 20 feet. See also Snellen vision.


Ablate: To remove. From the Latin “ablatum” meaning to carry away. Applies in medicine to removal of tissue through laser or surgical treatments.


Accommodation: The dynamic adjustment of the optics of the eye to keep an object focused on the retina from near to far, and vice versa. This is accomplished by contraction and relaxation of the ciliary body to change the lens shape. Change in the lens shape alters its focusing power.


Accommodative Intraocular Lens: A newer type of intraocular lens implant that is placed in the eye during cataract surgery that provides focused vision for near, intermediate or far objects. Traditional lenses provide vision at a single distance from the eye. Several models of lenses exist – some with concentric circles of variable powered lenses, some with flexibility in the lens to move with the eye. The need for glasses is reduced following the surgery.


Afferent papillary defect (APD): A test in which a flashlight is moved between the two pupils of a patient and the reactions/reflexes of the pupils to the light is observed, the “swinging flashlight test”. An abnormality in the pupil reaction may indicate an optic nerve, retina, or neurologic problem.


Age-related macular degeneration (AMD): A disorder of the central macular region of the retina in which the deepest, supporting layers of the retina do not function properly. AMD is a macular degeneration related to age and by definition, affects those older than age 55. The dry or atrophic form is the stage in which the deep layers are not functioning properly and evidence of this is seen as drusen (small yellow deposits) or an atrophic (thinned/fragile) appearance of the retinal pigment epithelial cells (RPE). The wet or neovascular form occurs when abnormal blood vessels, called neovascular vessels, invade the layers of the retina causing disruption, and possible hemorrhage or scarring. The wet form should be evaluated as soon as possible (within one week ideally) to see if any treatments are possible to stop or reverse the damage.


Amaurosis fugax: Temporary and complete loss of vision in one eye lasting 10 minutes to 2 hours. It may be associated with a small clot that is visible in a retinal vessel.


Amblyopia (Lazy Eye): Unilateral or bilateral reduction in vision that arises from an incomplete development of the brain’s interpretation of visual signals. Amblyopia develops most frequently in children who have an imbalance in vision where one eye can see better than the other eye. The brain learns to predominantly use the vision from the better eye. Unless detected and treated before age 7, amblyopia can become permanent.


Anisocoria: A difference in size between a person’s two pupils


Anisometropia: A moderate difference in refractive error between the two eyes. For example, one nearsighted, the other farsighted, or different degrees of either between the two eyes.


Anterior Chamber: The space in the front of the eye between the iris and cornea.


Aqueous Fluid/Humor: Clear, watery fluid generated by the ciliary body that flows forward through the pupil to nourish the lens and cornea.


Astigmatism: A warping of the cornea (the window of the eye) that causes light to be refracted (bent) unevenly, resulting in distorted vision. Pulling on eyelids sideways towards the ear can induce astigmatism.


Atrophy: Thinning of a tissue


Automated Lamellar Keratoplasty: A refractive surgery procedure used to treat relatively high degrees of myopia and some cases of hyperopia. This procedure uses only the microkeratome and is not as accurate as the laser procedures that are currently available.


Avastin (bevacizumab): A full-length monoclonal antibody produced by Genentech, Inc. (South San Francisco, CA) that binds and neutralizes the action of all biologically active forms of the vascular endothelial growth factor (VEGF) protein. Avastin was approved by the FDA for the treatment of metastatic colon and rectal cancer in 2004 but is used in an off-label fashion for many other medical indications.


Binocular Vision: The brain’s ability to blend the two separate images from each eye into a single image, creating depth perception.e


Blepharitis: A buildup of dandruff-like debris in the eyelashes and the clogging of the oil glands that causes chronic inflammation of the eyelid margins. This common condition can occur at any age and has symptoms of eyelid edge redness, burning, itching, swelling and crusting. Proper treatment requires frequent washing of the eyelashes with warm water and a mild cleanser (like Cetaphil Gentle Skin Cleanser), and occasionally, medicated ointments if prescribed.


Blind Spot: Every eye has a normal blind spot in the visual field that corresponds to the small area of the retina where the optic nerve enters the eye.


BOTOX (botulinum toxin): A neurotoxin protein used in very small doses to reduce the action of muscles in spasm conditions, or cosmetically to reduce the appearance of wrinkles produced by Allergan Inc. (US). Botox was used first in humans in 1980 by a local ophthalmologist, Alan Scott MD, to successfully treat strabismus (crossed eyes). The drug was approved by the FDA in 1989 for the treatment of strabismus, blepharospasm and hemifacial spasm in patients older than 12 years of age. The FDA expanded its approval of Botox in 2002 to include a cosmetic indication to temporarily improve the appearance of moderate-to-severe frown lines.

Bowman's Membrane: The micro-thin second layer of the cornea that lies just below the epithelium, or outer layer.


Cataract: A gradual clouding of the normally clear crystalline lens of the eye, caused by the natural aging process, metabolic changes, injury, various forms of radiation, toxic chemicals and certain drugs.


Central Retinal Artery: The main blood vessel that delivers blood to the retina from the carotid arteries through the optic nerve.


Central Serous Retinopathy (CSR) aka Idiopathic Central Serous Chorioretinopathy (ICSC): A condition affecting the central retina in which fluid accumulates between the deep layers of the retina – either under the retinal pigment epithelium (RPE) or between the RPE and photoreceptor layer. Symptoms can include a partially translucent brown/gray spot in the central vision or distortion of straight lines. CSR generally affects individuals ages 20-50 during stressful times. Fluorescein angiography and OCT are used to evaluate the disorder. Treatments include reduction of stress, observation, or laser therapies.


Chalazion: A red, swollen, sometimes painful bump on the eyelid caused by a localized inflammatory process due to a clogged oil gland (meibomian gland). The edge of the eyelids has the openings of about 20 oil glands that normally produce the outermost oil layer of the tear film. Sometimes old skin, makeup, dirt or heat can clog the pores preventing the normal flow of oil. The oil backup accumulates in the eyelid skin and causes an irritation. The body’s natural response is to wall-off the irritation in a fibrous capsule that can remain for months. The best prevention is keeping the eyelashes clean with regular washing with a mild cleanser such as Cetaphil. If a chalazion develops, frequent 1-2 minute warm-hot compresses can help unclog the pore and release the trapped oils. Sometimes surgical excision in the office of the fibrous tissue or oil is necessary.


Choroid: An intricate pigmented network of blood vessels that lies between the retina and the sclera that provides oxygen and nourishment to the outer layers of the retina.


Choroiditis: An inflammatory condition affecting the choroid due to infection, autoimmune or other causes.


Ciliary Body Muscles: A circular muscle that lies directly behind the iris that fattens and thins the crystalline lens by contracting and relaxing to focus images. The ciliary body also contains pigmented tissue that can be a source of inflammation in iritis.


Ciliary Processes: Extensions of the ciliary body that secrete the aqueous humor fluid.

Collagen: The main protein of animal connective tissue that helps give the eye its structure. It is the main component in the cornea and sclera.


Color vision: The ability to see color due to the presence of color detecting pigments in the photoreceptor layer of the retina. Some individuals have deficits in color vision due to a lack or reduction of certain pigments in their cone photoreceptors from birth. Color vision is commonly tested using Ishihara color plates that have colored numbers embedded in a sea of dots.


Concave Lens: A lens that is thinner in the center. It is used to neutralize nearsighted refractive errors.


Cone photoreceptors: Specialized pigment containing cells that form part of the outer layer of the retina. These cells are responsible for color and fine vision and are most populous in the macula. ‘Color blindness’ results from a defect in one or more of the pigments in cone photoreceptors.


Congenital hypertrophy of the RPE (CHRPE): Focal areas of pigment in the deep retina which are flat and well demarcated. These are caused by an overgrowth of the pigment in the RPE cells (see definition below). Many are present from birth, but some patterns of pigment may be indicative of a systemic syndrome.


Conjunctivitis: An inflammation of the eyeball's outer layer from viral or bacterial infection, allergy or other irritation. Redness, swelling, itching and watering are common symptoms.


Contrast Sensitivity: The ability to see differences in shades of light and dark objects. A white car in fog, or a black cat at night are examples of difficult contrast situations. Formal charts with grades of black to light gray letters are available to formally test this vision.


Convex Lens: A lens that is thicker in the center. It is used to neutralize farsighted refractive errors.


Cornea: The outer, clear, dome-like window that covers the iris, pupil and anterior chamber. It provides the majority of focusing power for the eye.


Corneal Ulcer: An abnormal and concerning whitening of an area of the cornea usually caused by bacterial or fungal infections. Eyes with ulcers are usually red and painful.


Crystalens:  An accommodating intraocular lens (IOL) which, like other premium multifocal implants such as ReStor and ReZoom, can provide a greater range of vision than the traditional monofocal IOL used in cataract or certain refractive surgical procedures.


Cycloplegic: Medications that cause paralysis of the ciliary muscle and therefore inhibit the dynamic focusing ability of the eye.


Diabetes: A disease in which the body does not properly regulate the amount of sugar in the blood causing the amount of sugar in the blood, or ‘sweetness’, to be too high/sweet. Diabetes is often caused by an abnormality in the production or effects of the hormone insulin to regulate the blood sugar. These abnormalities may be controlled with changes in eating habits, exercise and/or with medications. The hemoglobin A1C test (HbA1C) is most important in monitoring the effects of diabetes on the body. See HbA1C below.


Diabetic Retinopathy: Damage to the fine blood vessels of the retina that reduces oxygen supply and nourishment to the retina. The damage can lead to swelling of the retina (macular edema), growth of abnormal blood vessels (neovascularization), bleeding into the center of the eye (vitreous hemorrhage), or retinal detachment. Control of the sweetness of the blood is necessary to prevent diabetic retinopathy. For more information, see About your Eye.


Dilation: The temporary widening of the pupil with eye drops to allow examination of the retina, vitreous and optic nerve. Near vision may be blurred for several hours after dilation due to the eye drops effects on the ciliary body.


Diopter: A unit of measurement used in optics to describe the degree of correction with respect to nearsightedness, farsightedness and astigmatism.


Drusen: In the retina, small yellow deposits in the deep layers of the retina that result from an accumulation of material that may or may not be associated with retinal diseases. For more information on retinal drusen, please see the Macular Degeneration topic under About Your Eyes. In the optic nerve head, deposits between the nerve fibers that may or may not cause areas of visual field defects.


Dry Eye Syndrome: A condition caused by a reduction in quality and quantity of tears that can cause mild to severe eye discomfort. For additional information on Dry Eye Syndrome, please see the Dry Eye topic under About Your Eyes.


Ectropion: A condition that occurs when the skin of the lower eyelid turns outward which can lead to eye redness, dry eye and tearing.


Edema: Swelling in a tissue


Endothelium: The single inner layer of cells lining the inner surface of the cornea keeps the cornea clear by pumping fluid from the cornea.


Entropion: A condition that occurs when the lower eyelid turns inward which can lead to irritation from the eyelashes rubbing on the cornea.


Epiretinal membrane (ERM) aka macular pucker aka cellophane retinopathy: A very thin translucent layer of fibrous tissue on the surface of the macula that can contract/wrinkle causing a distortion of vision or thickening of the retina. Many ERMs do not have symptoms and are not dangerous to the eye.


Extraocular motion (EOM): The ability of the eyes to move up, down, left, right, in and out in a coordinated fashion. Six extraocular muscles work together to relax and contract to perform these motions – four rectus muscles and two oblique muscles per eye.


Flashes and Floaters: Streaks of peripheral bright light (like a car’s headlight streaking through a window, or a camera flash) and fine hair-like particles that float in the vision due to the gradual liquefaction of the vitreous (the gel substance that fills the eye) that happens in all people with time. Floaters are shadows of the vitreous fibers that become visually evident as they separate from the retina and clump together – similar to cobwebs. Flashes originate from the tugging on the retina as the vitreous gel liquefies. If more than 3 string-like floaters or hundreds of small dots are seen in one eye, this could be a sign of a retinal tear and a dilated examination of the eye is necessary within 24 hours. See also Posterior vitreous detachment.


Fluorescein Angiography (aka FA): A test to visualize the blood vessels in the retina and choroid in which a yellow fluorescent dye is injected into an arm vein and photographic pictures are captured as the dye passes through blood vessels in the eye. Normal and abnormal changes in the blood vessels can be seen with this test that takes less than 30 minutes. This test is commonly performed for diabetic retinopathy, macular degeneration and other retinal diseases.


Focal Point/Focus: The refraction of light rays by the cornea and the crystalline inner lens to a single point on the retina in a precise, natural manner that gives sharp, clear and colorful images.


Follicles: Gray-white round-oval elevations on the conjunctiva caused by the enlargement of normal immune lymphoid cell clusters that reside in the conjunctiva when exposed to certain infections or toxins. Follicles assist with the body’s immune defense system.


Fovea: The retina is the ‘film’ that lines the back of the eye and captures images. The macula is the central 6 mm of the retina responsible for central vision like face recognition and reading. The fovea is the central part of the macula responsible for the sharpest central vision.


Fundus: The inner linings of the eye, including the retina, optic disc and macula, which can be seen during an eye examination by looking through the pupil.


Glaucoma: A vision-threatening disease that causes optic nerve damage. The eye is like a camera that takes a picture and the optic nerve delivers the picture to the brain for processing – similar to a DSL or telephone cable. Humans are born with over 1 million fibers in the optic nerve ‘cable’ and it naturally thins with time, similar to hair or skin. But glaucoma is the condition in which the optic nerve thins prematurely, similar to balding. This premature thinning can be made worse by high eye pressure caused by poor drainage of a fluid (aqueous humor) from the eye, but often happens also with ‘normal or low’ eye pressures, probably due to insufficient microvascular blood supply to the optic nerve.


Goldmann applanation tonometry: The measurement of the intraocular pressure using a round 3.06mm Goldmann prism instrument attached to the slit lamp. An eye drop with a fluorescein dye and topical anesthetic is applied to the eye to allow visualization of the prism’s measurement. Goldmann is considered the ‘gold standard’ of measuring eye pressure.


Gonioscopy: The use of a gonio prism lens to examine the drainage channels in the front of the eye between the cornea and iris for its configuration, and presence of scarring or abnormal blood vessels.


Graves’; disease: An autoimmune disorder in which antibodies are produced against the thyroid gland. It is the most common cause of hyperthyroidism and enlargement of the thyroid gland, known as a goiter. The antibodies may also attack the extraocular muscles of the eye causing exophthalmos, or protrusion of the eyeballs.


Hemoglobin A1C (HbA1C): A blood test used to measure the control of diabetes. The elevated blood sugars in an uncontrolled diabetic person can cause extra sugar to be deposited onto the surface of red blood cells over time, ‘sugar-coating’ the blood cells. These ‘sugar-coated’ blood cells become lodged in the fine capillaries throughout the body and can cause permanent loss of these fine blood vessels. HbA1C measures the amount of ‘sugar-coating’ that has accumulated over 3 months on a blood cell – healthy individuals have an A1C under 5.5. A well-controlled diabetic has an A1C under 6.5-7.0.


Herpes Zoster (shingles): The reactivation of the chicken pox virus that has been hibernating in the body since the initial childhood infection due to various triggers which can include stress or fatigue. The virus may reactivate on the skin or in the eye and can cause corneal, uveitic or retinal inflammation that sometimes may lead to scarring. A herpes zoster rash that affects the forehead, eyelid or nose has the highest chance of eye involvement and warrants an ophthalmology examination.


Hertel exophthalmometer: A device used to measure the position of the eyes in the head relative to the orbital bones.


Hordeolum (stye): A red, swollen, sometimes painful cyst-like bump on the edge of the eyelid caused by a localized inflammatory process due to a clogged oil gland. See also Chalazion.


Hydroxychloroquine: see Plaquenil


Hyperopia (Farsightedness): A condition in which light is focused behind the retina, leading to blurred vision. Hyperopia can occur from a cornea that is too flat and/or an eye that is shorter than normal. Antonym: myopia. See also: presbyopia.


Indocyanine green (ICG): A special dye used in retinal angiography to evaluate deeper levels of the retina and choroids.


Infiltrate: A white area in eye tissue that usually represents an area of inflammation (white blood cell accumulation) with many possible causes including infection or other inflammatory causes.


Intraocular lens implant (IOL): An artificial lens made of silicon or acrylic plastic that is implanted inside the eye to replace or enhance the natural lens during cataract or refractive surgery.


Intracorneal Lens: A prescription lens implanted in the corneal tissue to correct nearsightedness / myopia.


Intraocular Pressure: Pressure of the fluids (aqueous humor and vitreous) inside the eye, which varies among individuals and is not related to blood pressure. Sustained high intraocular pressure may lead to optic nerve damage known as glaucoma.


Iris: The colored ring of the eye that gives people their ‘eye color’. This dynamic tissue of muscle and pigment is suspended behind the cornea and immediately in front of the lens. The iris regulates the amount of light entering the eye by changing the size of the pupil.


Iritis: An inflammation of the iris and surrounding tissues, resulting in an eye that is red, uncomfortable and sensitive to light. Iritis may be caused by an infection or infectious exposure, trauma, or autoimmune disease and is treated with eye drops to relax the iris and steroids. Sometimes systemic treatment is necessary. Patients with iritis should be seen regularly by their ophthalmologist until the episode has completely resolved because severe scarring and glaucoma can develop as a consequence.


Keratitis: An inflammation of the cornea. Keratitis can be an abrasion, bacterial, viral or fungal infection, or autoimmune diseases.


Keratoconus: A thinning of the central part of the cornea that can cause an outward bulge in the cornea. The cornea may become cone shaped, producing moderate to severe astigmatism and blurriness. Some individuals with keratoconus may be treated with rigid contact lenses while others may need surgical treatments.


Keratometer: An instrument that measures the front curvature, or steepness of the cornea, comparing high and low points to determine if a corneal focusing (refractive) problem exists.


Lacrimal Gland: The small, almond-shaped tissue, located under the eyelid and above the outer corner of the eye, which produces tears.


Laser: The acronym for Light Amplification by Stimulated Emission of Radiation. Different wavelengths and forms of this technology are used to treat retina and glaucoma disorders, as well as in vision correction procedures and refractive surgery.


Laser peripheral iridectomy (LPI or PI): An office laser procedure used to make a small hole(s) in the peripheral iris. An LPI is most commonly performed to prevent a sudden narrow angle glaucoma attack in people with compact drainage channels in the front of their eyes.


LASIK: The acronym for Laser In Situ Keratomileusis, LASIK (San Francsico) is a revolutionary vision-correction procedure for the treatment of refractive problems including nearsightedness, farsightedness and astigmatism.


Lattice degeneration: Thinning in patches of the peripheral retina that can lead to retinal holes and subsequent retinal detachments. Areas of high risk lattice degeneration can be secured with retinal laser treatment in the office.


Legal Blindness: Best corrected visual acuity of 20/200 or worse in the better eye with corrective lenses, or a visual field restriction of less than 15 degrees.


Lens: The clear, double convex structure suspended between aqueous and vitreous behind the iris, which helps to focus light on the retina.


Lensectomy: A surgical procedure that replaces the natural lens of the eye with a prescription lens for cataracts and severe cases of nearsightedness and farsightedness.

Limbus: The outer edge of the cornea where the cornea transitions to the sclera.


Low Vision: Visual loss, which cannot be corrected with eyewear or contact lenses and interferes with daily living activities. Individuals with low vision may have good Snellen (20/xx) vision, but may not be able to function well due to poor peripheral visual fields, poor contrast sensitivity, or ‘holes’ or scotomas in the vision. Many low vision aides and occupational/rehabilitation therapies are available. Low vision devices may include hand-held or stand magnifiers, telescopes, electronic digital magnifiers, large button telephones and calculators, tactile devices for stoves and thermostats, kitchen/cutting aides and many more.


Lucentis (ranibizumab): A monoclonal antibody fragment produced by Genentech, Inc. (South San Francisco, CA) specifically for injection into the eye for the treatment of neovascular age-related macular degeneration that binds and neutralizes the action of all biologically active forms of the vascular endothelial growth factor (VEGF) protein. Lucentis was approved by the FDA for the treatment of neovascular AMD in June 2006.


Macula: The retina is the ‘film’ that lines the back of the eye and captures images. The macula is the central 6 mm of the retina responsible for central vision like face recognition and reading. The fovea is the central part of the macula responsible for the sharpest central vision.


Macular Degeneration: A disease of the central retina in which the deepest, supporting layers of the retina do not function properly. Macular degenerations may be age-related, due to high levels of near sightedness or myopia, caused by infection or other genetic factors. The dry or atrophic form is the stage in which the deep layers are not functioning properly. The wet or neovascular form occurs when abnormal blood vessels, called neovascular vessels, invade the layers of the retina causing disruption, and possible hemorrhage or scarring. The wet form should be evaluated as soon as possible (within one week ideally) to see if any treatments are possible to stop or reverse the damage.


Microkeratome: A fine surgical instrument used to sculpt micro-thin layers of corneal tissue in LASIK and refractive surgery.


Micron: A unit of length equal to one-thousandth of a millimeter.


Monovision: A refractive technique used to reduce the effects of presbyopia in which one eye is used for distance and the other eye is used for near vision. Monovision may be provided with contact lenses or LASIK refractive surgery. Many public speakers have used monovision to read the text of a speech with one (near) eye, and the other eye corrected for distance to see the audience.


Myopia (Nearsightedness): A condition in which light is focused in front of the retina producing a blurry image. Myopia can result from a cornea that is too steep, a lens that is too strong, and/or an eye is too long.


Neovascularization: The abnormal growth of fine, breakable blood vessels from preexisting normal blood vessels in many diseases and tissues.


Nevus: A benign, pigmented growth that can occur in different parts the eye including on the eyelid, conjunctiva, iris or in the choroid. These are monitored regularly by an ophthalmologist to monitor for the unlikely, but possible transformation to a melanoma which would require further evaluation and treatment.


Ophthalmologist: A doctor of medicine who has graduated from a 4 year medical school, completed one year of a medical internship to understand the interactions and diseases of the whole body, and then completed three years of an ophthalmology residency to further specialize in the structure, function and diseases of the human eye.


Optic Cup: The lighter, cup-like area in the center of the optic disc. Humans have a range of normal cup sizes and serial observations are needed to determine if unexpected changes are occurring that could result in glaucoma.


Optic Disc/Optic Nerve Head: The circular area (disc) where the optic nerve connects with the retina.


Optic Nerve: The bundle of 1.2 million nerve fibers that carry the image collected by the retina to the brain, analogous to a DSL or telephone cable transferring information.


Optical Coherence Tomography (OCT): An office imaging device that uses safe laser beams to scan parts of the eye to measure the thickness and to document the anatomy of tissues. It is commonly used to measure the thickness of the retinal nerve fiber layer (RNFL) in optic nerve and glaucoma conditions, and the anatomy of the 10 central retinal layers in macular conditions. Applications for the cornea and iris are rapidly emerging.


Optical Zone: The central area of the cornea that is responsible for a majority of the refractive focusing functions of the eye.

Optician: A specialist in fitting eyeglasses and making eyeglass lenses to correct vision. An optician does not measure a glasses prescription, but is responsible for making and fitting the glasses or contact lenses.


Optometrist: A doctor of optometry who has graduated from a 4 year optometric school to specialize in the optics of the eye and methods of correcting optical abnormalities with eyewear, contact lenses, low vision aids and vision therapy for adults and children. Optometrists may provide routine screening examinations and are licensed in California to treat infections, allergy and glaucoma with medications.


Pachymeter: The ultrasonic medical instrument used to measure the thickness of the cornea.


Papillae: Small elevations on the eyelid (palpebral) conjunctiva with a fine central blood vessel in each elevation that occur as a reaction to various exposures including allergy, dryness, bacterial infections, contact lens/solution exposures, and other irritations.


Peripheral Vision: Side vision; ability to see objects and movement around the direct line of vision.


Phoropter: The instrument with several round dials that a patient looks through that is used to measure the amount lenses needed to correct myopia (nearsightedness), hyperopia (farsightedness) or astigmatism.


Pinguecula: A slightly raised, yellowish thickening of the white part of the eye (conjunctiva) next to the cornea, usually caused by chronic eye surface dryness, repeated sun or wind exposure.


Pingueculitis: An inflammation of a pinguecula to become more red, triggered by an increased exposure to sun, wind, surface irritants like dust, or allergy.


Phakic: Refers to an eye that possesses its natural lens.


Plaquenil / hydroxychloroquine: A medication used to treat autoimmune diseases including rheumatoid arthritis and lupus that can accumulate in the cells of the retina causing vision problems. The recommended dose for eye safety is less than 6.5mg/kg/day. Symptoms of toxicity may include central ‘tinkerbell’ lights or distortions and an annual dilated exam with either an Amsler grid test or visual field test is recommended by the American Academy of Ophthalmology.


Posterior Chamber: The space in the center of the eye between the back of the iris and the lens capsule that is filled with aqueous fluid.


Posterior vitreous detachment (PVD): The normal age-related liquefaction and separation of the vitreous gel and microfibers from the optic nerve and peripheral retina. In childhood, the vitreous is a near solid gel that fills the eye, similar to clear Jell-O. In the 20s, the gel begins to slowly liquefy in pockets. By ages 40-70, the liquefaction process is completed and the 1000+ vitreous fibers slowly, individually have separated from the retina. A posterior vitreous detachment is the separation of the last fibers from the retina which may or may not produce symptoms of flashes and hair/jellyfish/cobweb-like floaters. A dilated fundus exam is recommended to make sure no retinal tears have been pulled during this event. See also flashes and floaters.


Presbyopia: A condition that becomes symptomatic around ages 40-45, in which the zooming or focusing capacity of the eye decreases and, in time, is less able to focus up close. Individuals with hyperopia are more symptomatic than those with myopia. People with myopia in the range of -1-3 diopters should retain their near vision when they take off their glasses because their natural focal point is in the reading distance range.


Prism: A transparent wedge of glass or plastic that is used to move a beam or image. Prisms can be used to correct double vision.


Pterygium: A wedge-shaped growth that can grow onto the cornea to different degrees, frequently caused by a long history of sun or wind exposure. Larger pterygia can cause irregular astigmatism, warping of the cornea, and impairment of vision if it grows to the corneal center.


Ptosis: Drooping of the upper eyelid caused by the inability of the levator muscle to elevate the eyelid. Ptosis may be present from birth or caused by age, trauma, or neurological disorders.


Pupil: The black circle in the center of the iris which is an adjustable opening that allows varying amounts of light to enter the eye.


Radial Keratotomy (RK): A surgical procedure to correct mild to moderate cases of nearsightedness and some cases of astigmatism that involves placement of radial surgical incisions in the peripheral cornea.


Refraction: An interactive test between a patient and eye care professional to determine the best eyewear or contact lens correction to correct a refractive error (myopia, hyperopia or astigmatism).


Retina: The retina is the light-sensitive layer of tissue or ‘film’ that lines the back of the eye and captures images that are sent through the optic nerve to the brain. The macula is the central 6 mm of the retina responsible for central vision like face recognition and reading. The fovea is the central part of the macula responsible for the sharpest central vision.


Retinal Detachment: A vision-threatening condition that occurs when the retina separates from the wall of the eye. Frequent causes of retinal detachment include retinal tears, thinning (lattice) or holes, as a complication of diabetic eye disease, or less frequently from inflammatory conditions in the eye. Retinal detachments may be sometimes be repaired in the office if detected early or may need to be repaired surgically in the hospital.


Retinal Pigment Epithelium (RPE): The single pigment cell layer that is the deepest layer of the retina that provides important support to the photoreceptors (rods and cones) and other parts of the retina. The RPE are created during fetal development from neural tissue and therefore do not regenerate.


Retinitis: An inflammation of an area of the retina


Retinitis pigmentosa (RP): A group of inherited diseases affecting about 100,000 individuals in the US that cause a progressive degeneration of the photoreceptor layer of the retina. Age of onset and the degree of visual impairment vary considerably between individuals, but retinitis pigmentosa generally becomes symptomatic with decreased night vision in adolescents and young adults. Peripheral and night vision are affected first and may gradually worsen. RP related diseases include Usher syndrome, Leber’s congenital amaurosis, rod-cone disease, Bardet-Bidel syndrome and Refsum disease.


Rods and Rod Cells: Specialized light-sensitive cells (photoreceptors) in the retina that provide motion and side vision and the ability to see objects in dim light (night vision).


Schlemm's Canal: The passageway located in the angle between the cornea and iris through which the aqueous fluid leaves the eye.


Sclera: The tough, white layer of the eye that, with the cornea, protects the eye and provides its shape. The sclera is covered on the outside by the translucent conjunctiva.

Selective laser trabeculoplasty (SLT): A laser procedure for patients with glaucoma that uses short pulses of low energy laser light to the trabecular meshwork to increase the drainage of fluid out of the eye.


Slit lamp: The instrument that consists of a high-intensity light source combined with a binocular microscope that is used to examine the structures of the eye. A chin and forehead rest support a patient’s head for the examination and the light source can be changed in intensity, direction and width as needed for different examination purposes.


Snellen chart/vision: An eye chart of 11 increasingly smaller lines of letters developed by Herman Snellen in 1862 which is a standard measurement of visual acuity. The vision is reported as a ratio of the ‘distance at which the test is given’/’distance at which a normal eye can read the letter’. Therefore vision of 20/20 indicates a test given at 20 feet/a normal eye can see the letter at 20 feet. And a vision of 20/100 – the reader can only see the letter at 20 feet where a normal eye can see the letter from 100 feet.


Strabismus (Crossed Eyes): Misaligned eyes in which one or both eyes are asymmetrically gazing inward, outward, upward or downward in the relaxed position.


Stroma: The central and thickest layer of tissue of the cornea.

Subconjunctival hemorrhage: A situation that occurs when a fine blood vessel of the conjunctiva (the fine skin covering the sclera) breaks and bleeds, resulting in a patch of red on the eye. The hemorrhage generally resolves by itself in 7-10 days. Aspirin or other anti-coagulants may make the hemorrhage more dramatic. Hemorrhages with any worsening of vision or pain should be evaluated. A subconjunctival hemorrhage is similar to a nose bleed.


Suture: A surgical thread or stitch used to hold together tissue such as an incision.

Systemic Disease: A disease that can affect the body in more than one specific area including endocrine disorders such as diabetes or thyroid disorders, or autoimmune diseases including rheumatoid arthritis or sarcoid.


Thyroid: An endocrine gland located on the front part of the lower neck that regulates how the body burns energy (metabolism), makes proteins, and indicates how sensitive the body should be to other hormones. The thyroid is regulated by the hypothalamus and pituitary in the brain, and can become dysregulated in diseases such as Graves’.


Tonometry: The process of measuring the intraocular (fluid) pressure of the eye with either a blue-light tonometer at the slit lamp or a digital instrument.


Topography: A test that maps the curvature of the cornea to evaluate it for irregularities.

Trabecular Meshwork: The spongy, mesh-like tissue located in the angle between the cornea and iris through which aqueous fluid (humor) flows to Schlemm's canal and out of the eye through ocular veins.


Uvea, Uveal Tract: The pigmented parts of the eye including the iris, ciliary body and choroid which lies under the retina.


Vasculitis: An inflammation of a blood vessel

Visual Acuity: The ability to distinguish details and shapes of objects which is a combined function of the focusing capacity of an eye, ability of a retina to capture the image, ability of the optic nerve to deliver the picture to the brain, and the ability of the brain to process the image. A problem in any part of the visual process can impair visual acuity. The ability to see the sizes of shapes in black and white is measured on a letter chart and is generally reported as Snellen vision of 20/xx. See Snellen acuity.

Visual Field: The entire area that can be seen with the eye, including peripheral vision. Particular deficit patterns on a visual field can represent different eye diseases such as glaucoma, optic nerve or brain disorders.


Vitreo-macular traction (VMT): An abnormal adhesion of a part of the vitreous interface to the retina causing traction that can thicken the retina and/or distort vision. These may spontaneously separate or may require surgical separation.


Vitreous: The colorless gel that fills the eye behind the lens and in front of the retina. The vitreous contains a fine meshwork of vitreous fibers that attach to the optic nerve and peripheral retina providing a fine scaffolding. With time, the vitreous fibers naturally separate from the optic nerve and retina – called a posterior vitreous detachment.


Wavefront: The use of light images to evaluate the way that waves of light pass through the visual system to detect problems with the way in which the optical system of the eye transmits light.

Wavescan Systems: New technology that records a "fingerprint" or precise, detailed analysis about the visual characteristics of the entire optical system. The information is integral to planning a more personalized approach to LASIK laser vision correction.


YAG Capsulotomy: The use of a YAG laser in the office to remove a hazy film over the back of an artificial lens called a secondary cataract or posterior capsular opacity. This procedure requires only a few minutes and is generally painless.


Zonules: The many radial fibers that suspend the lens in position and enable it to change shape during accommodation or focusing. Zonules radiate out from the lens to their attachment on the ciliary body similar to the rays of a sun.