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__________________________________________ LAYPERSON DEFINITIONSClick on the letter of the word you want to look-up. Also look at the Q and A Archives for specific topics. Number of Visitors Since 10/11/00
A B C D E F G H I K L M N O P R S T U V
Accommodation In younger people, under age 40, the lens is adjusted by the ciliary muscles to focus clearly for near as well as far vision. With age the lens is less able to change, eventually requiring reading glasses or bifocals for close work.
Characterized by a lack of color vision with poor visual acuity, nystagmus, and sensitivity to sunlight. No treatment is available except, for example, sunglasses for the sensitivity to light.
Age Related Macular Degeneration The most common form of macular degeneration is Age-related Macular Degeneration (ARMD). It is believed that one contributing factor of ARMD is excessive light exposure over a person’s lifetime. Limiting excessive light exposure (e.g., wearing sunglasses and a hat outside) and a diet rich in antioxidants as well as zinc may prevent or retard the development of ARMD. In general, the lighter a person’s complexion the greater the risk of ARMD. See Recent Breakthroughs and see Simulations under True Stories.
Albinism A hereditary condition in which darker pigment fails to form in the eye, hair and skin. In ocular albinism, visual acuity ranges from 20/40 to 20/200 (legal blindness), the eyes may dance (nystagmus) and the person is very sensitive to sunlight. No treatment is available, except dark sunglasses for the photophobia. See NOAH under Links.
Amblyopia Commonly known as Lazy eye. A loss of vision in a young child due to the eye not being used. The eye is normal but the brain tends to suppress or ignore the image received by the amblyopic eye. The most common causes include a muscle imbalance, a focusing problem, or a problem such as a cataract or corneal scar. Sometimes both eyes can be affected. See recent Breakthroughs and Announcements.
Angioid Streaks Fragmentation of Bruch’s membrane due to the degeneration of the elastic layers and development of subretinal fibrovascular tissue. Sometimes does not cause vision problems; however, can cause a reduction of visual acuity leading to legal blindness. Often associated with another disease such as sickle cell disease and certain syndromes.
Aniridia A hereditary eye problem in which the iris, the colored part of the eye, is absent. There is poor vision, sensitivity to sunlight, nystagmus, and a tendency to develop glaucoma.
Anisocoria A difference in the size of the two pupils. It is present in about 5% of normal children. The most serious cause of an acquired Anisocoria follows a head injury with some brain or nerve damage; a disease such as a tumor also causes it.
Anisometropia A difference in the focusing power of the two eyes. One of the major causes of amblyopia; the brain is not able to clearly focus both eyes simultaneously. This is a "hidden" cause of amblyopia and very difficult to detect without an eye exam.
Anterior Chamber Dysgenesis See Q and A section.
Aphakia An absence of the lens in the eye. The lens is removed during a cataract operation. The natural lens may be replace with an artificial lens during the cataract operation.
Astigmatism An irregular curvature of either the cornea (front of the eye) or the lens. If either structure is shaped more like a football rather than a basketball, light is not sharply focused on the retina. This results in blurry vision for both distance and near.
Atrophy Decay or wasting away. Dying.
Best’s disease Also called Vitelliform macular dystrophy. Causes atrophy of the RPE and photoreceptors in the macula. Late in the disease there is a loss of visual acuity to legal blindness and a blind spot in central vision. No treatment is available. See Q and A section about Best's disease.
Blepharitis An inflammation of the eyelids or lid margins. It is often caused by an infection. A chronic form produces a scaling or crusting of the lid margins. This is treatable by an eye doctor.
Legal blindness is defined as: 1) visual acuity of 20/200 (only being able to see the big E on the eye chart) or less in the best eye even with the eyes corrected by glasses or contact lenses; or, 2) The peripheral visual field is reduced to 20 degrees of visual angle or less. Twenty degrees of visual angle is about the size of a one foot ruler held at arms length. Bright Red Spots See Q and A about bright red spots on the white part of the eye.
CAM Treatment CAM is an abbreviation for Cambridge (England) where a new therapy for amblyopia was proposed that used rotating gratings (series of black and white bars). Patients would view the rotating gratings while they performed various drawing tasks on top of the rotating gratings. Research has shown, however, that CAM treatment is not effective at improving visual acuity in ambyopic children.
Carbidopa Carbidopa is a peripheral decarboxylase inhibitor. Dopa decarboxylase is an enzyme that converts levodopa into dopamine - a major neurotransmitter and neuromodular of cellular function. Carbidopa is sometimes used to prevent the peripheral conversion of levodopa into dopamine in peripheral sites such as the gut, thus allowing more levodopa to reach the brain where it can have therapeutic effects.
Cataract An opacity or haziness of the lens of the eye. A cataract is noticed particularly at night when oncoming headlights produce glare disability or/and discomfort. It may or may not reduce the vision depending on size, density and location. If a cataract reduces visual acuity significantly, an Ophthalmologist can replace the defective lens with an artificial lens. (See Simulations)
Chalazion In the eyelid there are a number of glands that produce lubricants for the cornea and eyelid. A Chalazion occurs when a gland become plugged, enlarged, or infected. The lid looks like it has a lump about the size of a small pea. Occasionally it occurs as a thickness within the lid. Warm compresses help some disappear; others require surgical removal by an Ophthalmologist.
Choroideremia Atrophy or decay of the choroid, choriocapillaris and Bruch’s membrane of the eye, leading to a severe loss of vision. Usually progresses to light perception by 50 years of age. Leads to night blindness tunnel vision and reduced visual acuity. No treatment available.
Chorioretinitis An inflammation of the back of the eye involving the choroid and retina. It may be due to a number of different diseases, which affect the body such as toxoplasmosis, histoplasmosis, sarcoidosis, tuberculosis and syphilis.
Choroid This is the vascular coat between the sclera and the retina, which furnishes blood and nutrition to the outer layer of the retina.
Choroiditis An inflammation of the back of the eye involving the choroid and retina. It may be due to a number of different diseases, which affect the body such as toxoplasmosis, histoplasmosis, sarcoidosis, tuberculosis and syphilis.
Coloboma A congenital (born with) problem with the eye that is related to a maldevelopment or underdevelopment of a part of the eye. It may involve the eyelid, or interior part of the eye (involving the choroid and occasionally the optic nerve). No treatment is available.
Cone One of the two light receiving retinal cells (the other is the rod) that is responsible for daylight vision (e.g., color vision, high visual acuity, bright light vision). The area of the retina that provides central or reading vision, known as the fovea, contains only cones.
Also sometinmes refered to as cone degeneration. The cones of the eye degenerate over time leading to visual acuity between 20/50 and 20/200 – legal blindness. There may be a progressive vision loss, abnormal color vision and photophobia. No treatment is available, except for dark sunglasses for the photophobia. Patients with cone dystrophies and cone degenerations benefit for rehabilitation services.
Cone Rod Degeneration Also called cone-rod dystrophy. Leads to a loss of visual acuity between 20/25 to 20/400 – legal blindness. First there is a loss of cone photoreceptors followed by a loss of rod photoreceptors. Visual fields may be restricted, abnormal color vision and photophobia. No treatment is available. See Q and A about cone-rod degeneration.
Conjunctivitis An inflammation of the thin transparent tissue layer within the eye containing blood vessels. The conjunctiva covers the outer surface of the eyeball, starting at the limbus (edge of the cornea) and extends backward to form a recess under each lid before coming forward and covering the inside surface of each eyelid. It contains mucous secreting cells that allow the eye to move smoothly in various directions. It also helps lubricate the cornea during blinking. A contagious and treatable condition.
Cornea The front part of the eye that acts as a window for the entrance of light rays. It is attached to the other outer coat of the eye, the sclera; the white part of the eye. The cornea provides a significant amount of focusing power for the eye (the rest is provided by the lens). Because it has many nerve fibers, an injury or foreign body causes significant pain and discomfort.
Cortical Blindness A person with cortical blindness will have normal eyes and normal optic nerves but, nevertheless, will not be able to see. The cause of the blindness is with the cortex or surface of the brain that contains 32 or more sites for visual information processing. More recently, the preferred term for such individuals is cortical visual impairment, because many people will not be totally blind but will exhibit unusual visual losses; for example, they may be blind to stationary objects but be able to see moving objects.
Cortical Visual Impairment See cortical blindness. Also see Past Featured Articles.
Cortex The surface of the brain. The word cortex is derived from the Greek name meaning "bark" (like tree bark). The visual cortex contains 32 or more areas devoted to visual information processing. Two major cortical pathways are the "What" and the "Where" visual pathways, that are devoted to what an object is and where an object is.
Cover Test A test for a muscle imbalance. While the person is looking at a distant object, one eye is covered and then uncovered (cover-uncover). This is repeated on the other eye. Finally it is performed on both eyes, covering one then the other (alternate-cover). If one or both eyes shift during this test, there is a problem with alignment of the eyes. The misalignment with the eyes often cannot be seen with both eyes opened.
Cupping of the Optic Disc A depression of the optic nerve where the optic nerve leaves the eye. In glaucoma, the cup may be enlarged indicating damage to the nerves leading from the eye to the brain.
Cycloplegia A paralysis of the ciliary muscles following the instillation of eye drops. This produces a loss of accommodation or focusing ability. With the lens relaxed, a better estimate of the refractive error is possible in most cases. Most cycloplegic eye drops also dilate the pupil. Cycloplegia may last from a few hours to several days, depending on certain factors such as skin color – the lighter the longer.
Degenerative Myopia Pathologic progressive myopia. Causes RPE and choriocapillaris atrophy and photoreceptor degeneration. Leads to reduced visual acuity, night blindness and retinal detachment, the latter requires retinal surgery.
Dermoid Cyst A congenital (born with) tumor present in infancy as a yellowish swelling on the surface of the eye. It may enlarge during puberty. The dermoid cyst can be surgically removed by an ophthalmologist.
Detached Retina A condition in which the retina separates from another layer of cells in the back of the eye, resulting in a decrease in nutrition and visual function. It may be due to a hemorrhage, trauma, tumor, vascular malformation or from traction of the vitreous to which it is attached. Sometimes, people with high myopia will develop a retinal detachment, which requires emergency surgery.
Diabetic Retinopathy Pathologic changes in the back of the eye, retina, caused by diabetes. Background type is characterized by ongoing microaneurysms, retinal hemorrhages and swelling of the central part of the eye, known as the macula. The proliferate type involves the growth of abnormal blood vessels in the retina and optic disk, blood leaking into the jelly part of the eye, known as the vitreous, and detachment of the retina. (See Simulations under True Stories)
Diopter The unit used to measure the amount of refractive or focusing power of the eye. It also refers to the strength of lens required to provide clear vision. In general, the higher the refractive error, as measured in diopters, the worse the eye.
Diplopia Commonly known as double vision. In children, diplopia is often associated with a muscle imbalance such as esotropia. A refractive error may also cause enough blurring that a person sees two objects.
Dominant Progressive Foveal Dystrophy Dominant Stargardt’s disease. A degeneration of the RPE and photoreceptors of the eye. Slowly progressive, leading to legal blindness later in life. Usually starts in the 20s to 40s. Results in decreased visual acuity, central scotoma and defective color vision. There is no treatment.
Drusen Amorphous, sub RPE material; probably the remains of the RPE as a result of atrophy. Associated, sometimes with aging and with ARMD. There may be no symptoms present in the early stages and may lead to a reduction in visual acuity later in life.
Dyslexia A learning problem in which a person has difficulty with letter or word recognition. Children often are of normal or above normal intelligence; however, they have difficulty reading and sometimes naming pictures of objects. More recent evidence suggests that dyslexia is a decoding problem based on phonemes – the basic language components. This is a higher cortical processing problem and NOT a vision or eye problem, per se.
Electroretinogram (ERG) A test that measures the functional integrity of the retina, including the rod and cone photoreceptors. Usually involves the use of dilating drops in the eye and use of a contact lens electrode.
Electrooculogram (EOG) A test of the functional integrity of the Retinal Pigment Epithelium (RPE) – a layer of cells next to the retina of the eye. The EOG involves electrodes attached to the inner and outer corners of the eye and the patient is required to look back-and-forth between two small lights in a large white globe (ganzfeld) with bright lights on and off.
Endophthalmitis An inflammation involving the internal parts of the eye – i.e., choroid, retina, ciliary body and iris. A very serious condition sometimes seen after an injury to the eye by a foreign object. Vision is severely threatened. Large doses of cortisone and antibiotics are often needed. May lead to the removal of the eye. Must be treated by an eye doctor ASAP.
Enucleation An operation in which the whole eye and the front part of the optic nerve are removed. It is usually performed when the eye contains a tumor or is blind and very painful.
Esophoria A tendency for an eye to turn inward a little bit. It occurs under certain conditions such as fatigue. An esophoria is sometimes uncovered by the cover test.
Esotropia Commonly known as "crossed eyes". One eye is constantly turned inward toward the nose. In children, esotropia may lead to suppression of the visual signals from the eye to the brain and lead to amblyopia and decreased depth perception. In adults with previously straight eyes (for example after head trauma), esotropia causes constant double vision.
Exophoria A tendency for an eye to turn outward a little bit. Occurs sometimes under certain conditions such as fatigue, bright sun light or prolonged use of the eyes.
Exophthalmos An abnormal protrusion of the eyeball often caused by thyroid disease or a tumor behind the eye. Medical treatment is necessary.
Exotropia Sometimes called "Wall Eyes". One eye is constantly turned outward. A child may have an exophoria which progresses to a stage where the eye is straight one minute and turned-out the next (as when daydreaming or in bright sunlight). This is called intermittent exotropia. May need surgical correction.
Farsightedness Also called hyperopia. A refractive error in which the light rays entering the eye are focused behind the retina. With moderate degrees of farsightedness, accommodation can compensate so that glasses are not required. In later life everyone loses the ability to accommodate (presbyopia) and reading glasses become necessary. Children, up to about the age of 8 years, are often farsighted.
Floaters Small condensations of cells in the vitreous body, the fluid in the eye, which cast shadows on the back of the eye, known as the retina. This is normally associated with aging. Floaters may indicate a more serious problem such as a retinal detachment. If you suddenly see a lot of floaters, please see your eye doctor. See Q and A about floaters.
Fluorescein Angiography Fluorescein Angiography is a diagnostic test used to assess pathology that affects the retina, choroid and/or iris of the eye. Fluorescein angiography is used to assess the blood flow of the eye and abnormal states are referred to as either hyperfluorescence or hypofluorescence relative to the normal amount of fluorescence. Fluorescein angiography involves an intravenous injection of sodium Fluorescein ( a dye) into the antecubical vein ( a vein in the arm) and then photographs are taken of the eye as the dye enters and leaves the blood system of the eye. The doctor will evaluate prefilling ( i.e., what the retina and choroid look like before the dye enters the eye), transit ( i.e., first passage of dye through the retina and choroid), recirculation (i.e., fluoroscien has become equally distributed throughout the eye and then starts to circulate through again) and later phase ( i.e., as the fluoroscien is eliminated from the body by the kidneys). The test lasts about 30 minutes. Nausea and vomiting are the most common side effects, occurring in about 5% or less of patients. Severe side effects ( e.g., anaphylaxis, death) have been reported but are very rare.
Fovea A central portion of the retina and macula that contains only cones. The fovea is the only part of the eye that is capable of 20/20 or better vision.
Fundus The back part of the eye that can be seen with an instrument called an ophthalmoscope. Visible features include the retina with its blood vessels, the optic nerve and choroid. The fundus surrounds the fovea, that part of the eye used for reading.
Fundus Flavimaculatus See Stargardt’s disease.
Glaucoma An abnormal condition in which the pressure within the eye is elevated to the point where the visual cells and nerves are affected. Glaucoma is major cause of vision loss and blindness. Medicines and surgery are needed to control the elevated pressure. African Americans are at increased risk for glaucoma. Glaucoma often will lead to a loss of side vision before central vision is affected. Often the patient will not notice the loss of vision until it is too late for treatment. (See Simulations)
Gonioscopy The examination of the internal angle between the iris and cornea. This is accomplished by placing a contact lens over the cornea. It is vital in all cases of suspected glaucoma.
Gyrate Atrophy Diffuse total choroid vascular atrophy of the eye. Leads to night blindness, tunnel vision, cataracts and reduced visual acuity. Patients are usually myopic. Treatment involves pyridoxine; arginine free diet to reduce ornithinemia. Poor prognosis and usually leads to legal blindness by the age of 40 years.
Hemianopia A loss of one-half of the field of vision; for example, all of the right side of vision is gone. This is sometimes seen in older people with vascular problems, in certain types of brain tumors or after head trauma. See Simulations for an example of this condition.
Hyperopia Commonly known as farsightedness. Most children are hyperopic and see things in the distance better than very close things.
Hyperphoria A tendency for one eye to drift upward. A vertical type of muscle imbalance between the eyes.
Hypertropia A muscle imbalance in which one eye is straight and the other is turned upward.
Hyphema Blood in the aqueous fluid - front part of the eye, often caused by an injury. Patient should seek immediate medical attention since a hyphema may lead to glaucoma and permanent loss of vision.
Iridocyclitis An inflammation of the iris and ciliary body. It may be due to a disease within the eye or occur as a reaction to an injury or disease elsewhere in the body.
Iris The colored part of the eye with a hole (pupil) in the center. It regulates the amount of light entering the eye – the dimmer the lighting the more light the iris lets into the eye by widening the pupil.
Iritis An inflammation of the iris. See whole page on Iritis (Eyeritis).
Keratitis An inflammation of the cornea often caused by a virus or bacteria. Scarring and loss of vision may result.
Keratoconus An inherited disease where the cornea becomes progressively shaped like a cone. Wearing a contact lens may slow the progression of the disease. Corneal transplant surgery may be required.
Keratoplasty A corneal transplant.
Lacrimal Gland The tear gland located under the upper eyelid at the outer corner of the eye. The fluid it secretes cleans and provides moisture for the cornea. It is responsible for tearing during emotional stimulation or following corneal irritation by a foreign body or chemical.
Lacrimal Sac The tear sac located on the side of the nose adjacent to the inner corner of the eye. Tears normally drain from the eye into the tear duct and then through the sac, finally leaving by a drain which enters the nose. The tear sac remains filled with tears when an infant has a blocked tear duct. An infection of the tear sac is called a dacryocystitis.
LASIK A refractive surgery that requires the cutting of a large "flap" of cornea and the removal of the inner layer of cells, usually by use of a laser, in order to change the refractive state of the eye. Risks include problems with glare, particularly at night, and surgical complications. If serious infection occurs, blindness could result. Long term risks are not known.
Lazy Eye A term often used instead of amblyopia. A loss of visual function, usually measured by visual acuity, in one or both eyes that cannot be explained by identifiable causes(s) such as a cataract or retinal disease. An eye that turns in (esotropia) or out (exotropia) may have a certain degree of central visual loss (amblyopia). A lazy eye is often treated by placing a patch over the stronger eye and forcing use of the lazy eye. The earlier the detection of the lazy eye the better for recovery of central vision with patching. If left untreated, after the age of about 8 or 9 years, patching therapy is no longer effective and the child will have a permanent loss of vision and loss of binocular vision and depth perception. (see recent breakthroughs and L-dopa treatment and Announcements.
L-dopa See Levodopa.
Leber’s Disease (Leber’s Congenital Amaurosis) A severe form of rod-cone degeneration present at birth. Infant’s have very poor visual acuity, photophobia and nystagmus. Infant’s with Leber’s will often constantly rub their eyes with their fists and poke their eyes with their fingers and thumb. No treatment is available.
Legal Blindness See Blindness.
Lens The lens of the eye is like an adjustable lens of a camera and focuses light rays on to the retina for sharp images. A condition called presbyopia occurs when the lens is no longer able to adjust for objects at different distances.
Lens capsule The lens capsule is a membrane that surrounds the lens of the eye. In cataract surgery, the lens is usually replaced with an intraocular lens but the lens capsule remains in the eye.
Levodopa Levodopa is a precursor for the neurotransmitter/neuromodular dopamine. Levodopa is usually referred to as "L-dopa" and is often used to treat older adults with Parkinson's disease. Through enzymatic action of Dopa Decarboxylase, levodopa is converted into dopamine. However, levodopa can be converted to dopamine in peripheral sites such as the gut and then will not be able to cross the blood-brain barrier for central therapeutic effects. To prevent peripheral conversion of levodopa to dopamine, a peripheral decarboxylase inhibitor, such as carbidopa, is combined with levodopa to increase the amount of levodopa into the brain where it is then converted to dopamine. Carbidopa cannot cross the blood-brain barrier.
Macula A specialized part of the retina containing mostly cones. The macula is used for all detailed visual tasks. The center of the macula is called the fovea. If a disease process harms or destroys the macula, vision is usually reduced to 20/200 (legal blindness).
Macular Degeneration A degeneration or loss of the macula of the eye, usually hereditary. The most common form of macular degeneration is Age-related Macular Degeneration (ARMD). It is believed that one contributing factor for ARMD is excessive light exposure over a person’s lifetime. Limiting excessive light exposure (e.g., wearing sunglasses and a hat outside) and a diet rich in antioxidants as well as zinc may prevent or retard the development of ARMD. In general, the lighter a person’s complexion the greater the risk of ARMD. See Recent breakthroughs. (See Simulations under True Stories and see Links)
Microphthalmus A congenital problem in which the eye(s) is (are) smaller than normal. Vision is often reduced because other problems present within such an eye. No treatment is available.
Mydriatic A drug that dilates the pupil (see cycloplegia). Sometimes used to treat amblyopia, particularly if the child will not wear an eye patch over the stronger eye.
Myopia Commonly known as nearsightedness. A refractive error in which the light rays focus in front of the retina producing blurry distance vision. External optical correction (glasses or contact lenses) are required for clear distance vision. It is now believed that myopia is partly hereditary; you’re more likely to become myopic if your parents are myopic. Also, near work can lead to a further worsening of the myopia. If the myopia is greater than 6 diopters, a condition known as high myopia, the possibility of retinal detachment is increased.
Nearsightedness See myopia.
Nystagmus A rapid involuntary movement of the eyes. Sometimes referred to as "dancing eyes". The most common form of nystagmus is horizontal, but vertical and rotary nystagmus is also seen. In children, it is often congenital and associated with reduced visual acuity. Nystagmus in infants and children may be associated with other problems, such as optic nerve hypoplasia or a retinal degeneration. In adults, it may signify a serious problem within the brain, such as a tumor. Nystagmus can also occur after a brain injury.
(OD) Ocular Dexter Right eye
(OS) Oculus Sinister Left eye
(OU) Oculus Uterque Both eyes
Ophthalmologist A physician (MD or DO) who specializes in the diagnosis and treatment of eye problems and diseases. The ophthalmologist works with the use of glasses, contact lenses, eye medication and surgery.
Optic Atrophy A disease of the optic nerve in which the nerve fibers carrying the electrical impulses from the eye to the brain start to die off. In such cases the optic nerve has a pale or whitish appearance compared to the normal pink color. Optic atrophy is associated with poor reading vision and often the cause of legal blindness. May be associated with a serious medical condition and requires further medical examination to determine the cause of the atrophy. Not reversible. See Q and A Archives section about Optic atrophy.
Optic Disc The visible part of the optic nerve inside the eye. The axons of the ganglion cells of the inner retina make-up the optic nerve.
Optician A technician who fits a person for glasses. He/she does not test for glasses. Some opticians also fit contact lenses.
Optic Nerve Composed of nerve fibers that carry visual information from the retina to the brain. Optic nerve damage causes a loss of vision.
Optic Nerve Hypoplasia A small and underdeveloped optic nerve. Optic nerve hypoplasia is one of the leading causes of vision loss and blindness in infants and children. Optic nerve hypoplasia occurs in the early stages of fetal development, when the eyes are forming. The optic nerve never fully develops or, once developed, dies-off and reduces in size for unknown reasons. Recent evidence suggests that ganglion cell axons, that make-up the optic nerve, are not able to grow through the optic nerve head because certain chemical messengers are not present for directional growth from the eye to the brain. Optic nerve hypoplasia is variable, and can result in only minor vision problems to complete blindness. Usually, if the infant has nystagmus the optic nerve hypoplasia is more severe and vision is very much reduced. If the infant does not have nystagmus, the likelihood for significant vision loss in less. All infants with optic nerve hypoplasia should have a CT scan or MRI to look for midline brain defects that can result in body growth problems. If the infant does not have nystagmus, the chance of midline brain defects is small. If the infant has nystagmus, the chance of midline defects is greater. Some infants have optic nerve hypoplasia in one eye only. If only in one eye, the chance of midline defects is very small and the doctor may chose not to do a CT scan or MRI, depending on other factors. There is no treatment or cure for optic nerve hypoplasia.
Optic Neuritis An inflammation of the optic nerve usually with some loss of sight (may be temporary). It may signify a more serious neurological condition. A leading cause of optic neuritis is multiple sclerosis (MS).
Optometrist (OD) A licensed non-physician educated to detect eye problems with special emphasis on correcting refractive errors. Depending on training, an Optometrist may use diagnostic and therapeutic medicines. An Optometrist does not perform surgery.
Peripheral Vision Also called "side vision". That part of vision that detects objects outside of where we are directly focusing our eyes. When we look directly at something we are using the fovea - that part of our retina where there is a high density of cone photoreceptors and thus allows for detailed vision. The fovea is part of the macula - that part of our retina with mostly cone photoreceptors and used for day time vision. Outside of the macula is what is typically referred to as peripheral vision, and peripheral vision is dominated by the rod photoreceptors. Peripheral vision is used mainly for detecting objects and in directing where we should fixate our fovea or central vision. Peripheral vision is used mostly during the night. Without peripheral vision, we would have "tunnel vision". If a person has a significant loss of peripheral vision the person would be legally blind. See legal blindness.
Photophobia Severe discomfort to bright lights. Usually a symptom of eye disease, such as glaucoma, in an infant or retinal disease in a child or adult. Sometimes treated with dark sunglasses.
Presbyopia The normal decrease in focusing power (accommodation) of the eye which occurs with aging. It begins about age twelve but becomes most noticeable to the average farsighted person after age forty. Bifocals or reading glasses are required for clear near vision.
PRK PRK stands for Photo Refractive Keratectomy which is a form of refractive surgery to correct a refractive error such as myopia. A laser is used to remove a front layer of cells of the cornea to change the refractive state of the eye so that glasses are no longer needed. Complications include under or over correction of the refractive error and glare problems, particularly at night with oncoming head lights. If serious infection occurs, blindness might result.
Pseudostrabismus A child's eyes appear to be out-of-alignment, and usually one eye appears to turn in. In infants this appearance is especially noticeable when there is excessive skin on either side of the nose that covers the inner corner of each eye. As the child looks to one side, part of the eye disappears under this skin and looks crossed. This condition is common in Asian - Americans.
Pterygium A triangular membrane with blood vessels which grows from the sclera toward the occasionally onto the cornea. It occurs more often on the nasal side of the eye. It is more common in dusty and windy climates. Surgery is often necessary.
Ptosis A drooping of the upper eyelid. In children it is usually a congenital problem. It rarely causes amblyopia. Most children simply hold their heads back if the droop is severe. Surgery, the only treatment, is usually suggested prior to starting school when the appearance is cosmetically unacceptable.
Pupil A circular opening in the center of the iris. The size of the pupil changes according to the amount of light present. It is small in sunlight and large in a dark room.
Red Eye See Q and A section about Red eye.
Refraction In order for an eye to see clearly, the light rays must come to a perfect focus when they reach the fovea. The bending of the light rays is called refraction. Each eye has its own characteristic refractive error. An instrument (retinoscope) is used to determine this error. The examination is called refracting the eye. From the refraction, the examiner learns the strength of lens necessary to provide the clearest vision for each eye.
Retina The inner lining of the back of the eye that contains the visual cells (rods and cones). The function of the retina and visual cells is to convert light rays into electrical impulses that are transmitted to the brain by way of the optic nerve.
Retinal Detachment A retinal detachment occurs when the retina, that part of the eye that contains the photoreceptors, detaches from the underlying layers of cells, called the choroid. A retinal detachment my be the result of injury to the eye such as blunt trauma (remember Sugar Ray, the boxer) or it may result from other things like high myopia or age-related macular degeneration. In certain diseases, retinal breaks and tears occur and these may lead to a retinal detachment. Early warning signs include bright dots or lights or some of your side vision may appear dark. A retinal detachment may be treatable if detected early, so see your Ophthalmologist. See Q and A section about retinal detachment.
Retinitis Pigmentosa (RP) A hereditary degeneration of the retina which leads to a severe loss of vision, usually legal blindness. Progressive symptoms include night blindness, loss of side vision leading to tunnel vision and decreased central vision and visual acuity. Visual acuity may be compromised early by the formation of cataracts, requiring cataract surgery. There are three main forms of RP based on heredity: dominant, X-linked and recessive. In the dominant form, about 50% of all family members have the disease. In the X-linked form, RP skips every other generation because females are carriers and males get the RP. In the recessive form, there is no family history or only sporadic occurrences of the disease. If one member of the family (e.g., older son) is diagnosed with recessive RP there is a 25% chance that the other brothers and sisters, with the same mother and father, have the disease. About 1 in every 3600 people have RP. A possible treatment to slow down the progression of the disease is the use of vitamin A palmitate (15,000 IUs/day). However, Vitamin A therapy for RP is controversial and women of childbearing age must NOT get pregnant while on vitamin A because of an association with birth defects. (See Simulations under True Stories and see Links)
Retinoblastoma The most common cancer in the eye occurring in early childhood. A parent or doctor may first suspect a problem by detecting whiteness in the normally dark pupil. Occasionally it leads to a wandering eye (strabismus). It does not spread from one eye to the other but about 25% have a tumor in each eye. Immediate medical treatment is necessary. Sometimes the eye(s) must be removed to prevent spreading of the tumor into the brain.
Retrobulbar Neuritis An inflammation of the optic nerve. It causes a loss in vision. It is sometimes indicative of a neurological disease.
Rod Cone Dystrophy A number of retina diseases in which the rod photoreceptors first start to degenerate followed by the cone photoreceptors. Other parts of the retina and RPE are also adversely affected. Symptoms include loss of side vision and night blindness followed by the loss of central vision. RP is the most common form of rod-cone degeneration. Some forms occur at birth while other forms may start much later in life. Generally very poor prognosis.
Rods The rods are the visual cells of the retina that are important for night vision and peripheral vision. The rods are the first affected in rod-cone degenerations such as RP.
Sclera The sclera is the white part of the eye. The clear cornea is the front extension of the sclera.
Scotoma An absence of vision in part of the visual field. It is present in such conditions as glaucoma, or in more serious diseases within the brain. Often detected by a visual field test. (See Simulations under True Stories)
Snellen Chart The familiar eye chart with larger letters at the top and smaller ones at the bottom. It is used for measuring central vision.
Staphyloma An abnormal bulging of the cornea or sclera. It is usually a congenital problem.
Stereopsis Also known as depth perception. The separation between the eyes provides for slightly different views of an object by each eye. The brain for the purpose of telling the location of an object in 3D space uses this difference in views between the eyes or disparity.
Strabismus Misaligned eyes. See exotropia, esotropia and hyperopia.
Stargardt’s Disease Also called Juvenile macular degeneration. Early in the course of the disease the retina may look normal to the eye doctor. Later in the disease process, there is a total loss of the RPE and photoreceptors in the macula. Disease progression is rapid leading to a central scotoma, reduced central vision leading to legal blindness and some loss of color vision by the age of 20 years. Patients sometime become photophobic. No treatment is available. Also see dominant progressive foveal dystrophy.
Tear Duct Part of the drainage system for the tears. The dilated part of the tear duct is called the lacrimal sac. An obstruction along the tear duct in infancy will cause a watery or draining eye. A warm compress is sometimes used to open a blocked tear duct. A tear duct probing surgery may be necessary to relieve the blockage.
Tonometer An instrument used to measure the pressure within the eye. This is one of several factors used in diagnosis of glaucoma. The results may also be used to follow the response of treatment to this disease.
Toxoplasmosis See Q and A section about Toxoplasmosis.
Trichiasis The inward turning of an eyelash. If it scratches the cornea, there is discomfort similar to a foreign body sensation.
Trachoma A viral infection of the cornea and conjunctiva which may produce scarring and impaired vision.
Tunnel Vision A reduced visual field in which the eyes only see straight ahead (no peripheral vision). It may be due to certain eye diseases, such as glaucoma or RP.
Usher’s Syndrome Characterized by a severe sensori-neural hearing loss at birth and followed by the development of RP. Usher’s syndrome is the leading cause of deaf-blindness. Occurs in about 1 in 33,000 births. However, in the deaf population about 1 in 50 have Usher’s syndrome. No treatment is available, but see RP.
Uveal Tract The entire vascular coat of the eye composed of the iris, ciliary body, and choroid.
Uveitis Inflammation of the uveal tract. It may be anterior involving the iris and ciliary body (iridocyclitis), or posterior involving the choroid (choroiditis).
Visual Evoked Potential (VEP) See Visual Evoked Response.
Visual Evoked Response (VER) The VER is a test of the function of the visual pathways from the retina, along the optic nerve and optic tract to the early parts of the visual centers of the brain. Usually, EEG electrodes are placed on the head and the patient is required to view a flashing light and an alternating pattern (e.g., stripes or checks) on a TV. The VER is a diagnostic test for such things as Multiple Sclerosis, optic neuritis, optic neuropathies, cortical visual impairment and certain types of brain tumors. The pattern VER can also provide an objective estimate of a patient's visual acuity, even if the patient is nonverbal (e.g., too young, comatose or mentally impaired).
Visual Suppression This occurs when the brain ignores the visual image being transmitted from one eye. It is not voluntary. In the younger child it is associated with strabismus and amblyopia. An eye that is misaligned or is out of focus is likely to be suppressed by the child.
Vision Therapy Vision Therapy is a term that refers to a mixture of so-called "therapies" that employ eye movement tasks, eye-hand coordination tasks, 3D tasks, etc., which purportedly improve everything from golf games to dyslexia to reading problems in children and adults. The vast majority of these claims are unsubstantiated. Vision therapy is usually not covered by insurance. Warning: before signing-up for Vision therapy, ask the provided to support his or her claims with scientific evidence that has been published in a peer reviewed scientific journal. Be skeptical of therapies that seem to good to be true - Caveat emptor.
Vitreous The transparent, solid, gelatinous material which fills the interior of the eye behind the lens. It allows the eye to maintain its shape. Return to TOP Return to Home Page
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W. R. Bryan Diabetic Eye Disease Research Fund 2008 OLERF Annual Report (PDF file) |
