Glossary
Terms and Definitions Relating to Macular Degeneration
Also published at
For diagrams, see “Anatomy of the Eye.”
A
Acuity – level of clarity, distinction, or sharpness.
Acuity test – use of an eye chart to measure accuracy of reading and perception at various distances. (See “Snellen Chart”).
Afterimage – continued visual perception after the source of the image has been removed.
AREDS – Age-Related Eye Disease Study, which recommended high dosages of certain antioxidant vitamins and zinc for early-stage AMD patients.
Alternative Treatment (or Medicine) – outside the realm of approved or generally-accepted intervention.
Amblyopia – diminished vision in one or both eyes without apparent physical reason, and despite best lens correction.
Amsler grid – a grid chart used for checking distortion in the vision and central vision defects.
Anesthesia – a drug-induced (anesthetic) decreased sensitivity to pain.
Aneurysm – localized, pathological, blood-filled dilatations of a blood vessel caused by a disease or weakening of the vessel’s wall.
Angiogenesis – new blood vessel growth.
Anterior – the front or forward portion.
Antiangiogenic – a general term for drugs which have the capability of preventing new vessel growth (neovascularization) in the retina.
Antioxidants – substances produced by the body which counteract the effects of free radicals. Present in dark green, leafy vegetables such as spinach and kale, and may also be acquired through supplements such as Vitamins C, E, and carotenoids, including beta-carotene.
Argon laser – laser light produced from argon gas. Nine separate wavelengths in the blue-green visible light spectrum are produced, but the main wavelengths are 488.0 nm blue and 514.5-nm pea green light.
Asymptomatic – no symptoms present.
Atrophic macular degeneration – “dry” macular degeneration.
Atrophy – a wasting of the tissue due to loss of nutrition or neural stimulus.
Automated perimeter – a computer-driven device used to plot defects in the visual field.
Autosomal dominant – a trait or disease that is produced when only one copy of a gene is present.
Autosomal recessive – a trait or disease that is produced only when two copies of a gene are present.
B
Best corrected visual acuity – a measure of best focus while wearing corrective lenses.
Beta-blocker – a drug (eg thalidomide) which inhibits the growth of blood vessels. Currently being studied as a cancer cure, with possible benefits in the field of macular degeneration.
Betacarotene – a yellow photopigment chemical synthesized by plants and present in vitamin A.
Bilateral – referring to both eyes.
Binocular vision – blending of the separate images seen by the two eyes. Normal binocular vision produces a stereoscopic image and parallax-induced depth perception.
Blind – a condition of the retina resulting in no sensory response to light.
Blind spot – a natural area of no vision in the outer periphery where the optic nerve enters the eye. Also, an area of no vision as a result of degenerated photoreceptor cells (see “scotoma”).
Blue light – potentially hazardous light rays that are near ultraviolet (400-500nm) and which cause production of free radicals in the retinal cells.
Brachytherapy – Radiation treatment delivered by a small plaque sewn to the sclera.
Braille – a system of raised dots on a page representing letters and words, invented by Louis Braille.
Bruch’s membrane – the tissue which separates the choroid (blood vessel) layer from the retinal pigment epithelial (RPE) layer of the retina. See Anatomy of the Eye.
C
Carotenoids – photochemical and photosensitive agents in plants and animals, composed of fat-soluble, highly-unsaturated pigmented organic chemicals.
Carrier – an individual with one mutated gene paired with one normal gene. A carrier of a gene for a recessive disease does not have the disease.
Cataract – a clouding of the crystalline lens of the eye or its surrounding transparent membrane, obstructing the passage of light and causing a reduction in vision.
Cell – the smallest unit of living matter. The human body is made up of about 10 trillion cells.
Central retinal artery – the vessel that delivers blood into the eye and supplies nutrients to the retina.
Central retinal vein – the vessel that carries blood away from the retina.
Choroid – the layer of the eye behind the retina containing blood vessels that nourish the inner cell layers.
Chromosome – a microscopic, rod-like structure in the cell’s nucleus that carries genetic material.
Classic – a type of wet macular degeneration wherein the leaking blood vessels are identifiable under magnification.
Clinical depression – a physical/mental state of depression that meets the criteria accepted by most clinicians and which lasts two weeks or longer.
Clinical testing (or trial) – direct observation of a living patient to answer specific questions about vaccines, therapies, or new methods. The four phases of a clinical trial are:
- Phase I: Determination of safety and side effects on 20-80 people;
- Phase II: Determination of effectiveness and safety on 200-300 people;
- Phase III: Confirmation of results on 1000-3000 people; and
- Phase IV: Studies done after FDA approval and public use.
Color vision – the ability to perceive differences in color, including hue, saturation and brightness.
Complication – an undesirable effect of a disease or its treatment.
Computerized perimeters test – an examination wherein the doctor uses a computer to present lights or other targets in various positions and map out the field loss areas.
Cone cells – the photoreceptor cells in the retina which are responsible for central and color vision under bright conditions (photopic Focal Points). See Anatomy of the Eye.
Confrontations test – and examination where the doctor moves his hand or lights in from the side to see if there is any loss of peripheral vision due to stroke.
Contrast sensitivity – the ability to differentiate between an object and its background.
Control group – that segment of an experimental study population that receives a sham, or fake, treatment.
Cornea – the transparent part of the front of the eyeball which covers the iris and pupil. See Anatomy of the Eye.
Cup/disc ratio – the area of the level part of the optic disc divided by the area of the deep part, or cup, of the optic disc
Cyst – a membrane sac containing fluid or semisolid matter.
D
Degeneration – deterioration as a result of chemical change or invasion of abnormal matter.
Degenerative myopia – loss of central vision caused by separation of the retina as a result of abnormal elongation of the eyeball.
Depth perception – the ability to judge the relative distance of objects and the spatial relationship of objects at different distances.
Diagnosis – the name of a disease or condition.
Dilation – the process wherein the pupil automatically enlarges to allow more light to reach the retina. Also, chemically-induced enlargement of the pupil by a doctor to allow easier examination of the interior of the eye.
Disciform AMD – the disciform (wet) type of macular degeneration involving neovascularization.
Disease – an abnormal and troubling mental/physical condition.
DNA – deoxyribonucleic acid, the molecule that holds genetic information. It is the biochemical molecule that makes chromosomes and genes.
Dominant eye – the eye which looks directly at an object, while the non-dominant eye views it from the side.
Double image (or “diplopia”) – a second image (usually dimmer) caused by the eyes not aiming equally on an object. Also called “ghosting.”
Double-blind (more appropriately “double-masked”) – a type of experiment in which neither the subject nor the administrator knows whether the test treatment is real or fake.
Dose-escalation (also “dose-ranging”) – an experiment wherein all subjects receive the treatment in different amounts of a drug to test for safety and efficacy.
Drusen [DRU-zen] – small yellowish, protein lipid deposits in the retina appearing in the early stages of dry (atrophic) macular degeneration. Two types: hard and soft, with the latter being more likely to signal future retinal problems.
Dry eye syndrome – a condition in which the tear ducts do not supply sufficient moisture to the eyeball, resulting in sensations of pain and stinging.
Dry macular degeneration (also “atrophic” macular degeneration) – the form of macular degeneration wherein the retinal cone cells degenerate due to age.
Dystrophy – degeneration, abnormal or defective development, insufficient nutrition.
E
Eccentric viewing – the practice of seeing peripherally as a substitute for loss of central vision.
Edema – an abnormal excess accumulation of fluid in a tissue.
Enzyme – a protein involved in an important biochemical reaction in the body. A defective enzyme can be the result of a mutated gene.
Experimental group – that segment of an experimental study population that receives the treatment being tested.
Exude – to discharge moisture.
Extrafoveal – outside of the fovea, or very center of the macula.
Eye – the organ of sight. Spheroid in shape, approximately one inch in diameter.
F
FDA – abbreviation for the United States Food and Drug Administration. Responsible for approving and regulating treatments, procedures, and pharmaceuticals.
Figure-ground perception – the ability to differentiate images from the background.
Flasher – an illusion of flashing light created when the vitreous gel, which fills the inside of the eye, rubs or pulls on the retina.
Floaters – small clumps of vitreous gel or cellular debris in the vitreous fluid.
Fluorescein [FLOR-eh-seen] angiogram (FA) – a procedure for viewing and photographing the inner eye nvolving injection of a non-toxic dye into the bloodstream.
Fovea – the concave center of the retina. The region of highest visual acuity and cone cell density. See Anatomy of the Eye.
Free radicals – atoms with single missing electrons, which cause cellular damage by taking electrons from molecules in healthy cells. This process is called oxidation.
Fundus [FUN-duss] photo – image of the back of the eye.
G
Gene replacement therapy – the procedure of introducing a non-defective gene into the body to take the place of a defective one.
Glare – intense light into the eyes causing discomfort.
Glaucoma – a condition in which the pressure inside the eye increases beyond the norm, damaging the optic nerve and causing loss of peripheral vision.
H
Headache (ocular) – cranial pain thought to result from eye disease or excessive use.
Hemorrhage – leaking of blood from the vessels.
Hypertension – high blood pressure. Possibly-but not proven to be-linked to the wet form of macular degeneration.
Hyperopia (or “far-sightedness”) – a condition in which rays of light from nearby objects are focused behind the retina, causing blurred vision.
Hypoxia – a deficiency of oxygen supply to a tissue.
I
Idiopathic – a disease having no known cause.
Informed consent – The process of learning key facts about a clinical trial before participating, including:
Why the study is being done
What is to be accomplished
What will be done and for how long
What risks are involved
What benefits can be expected
What other treatments are available
Whether the subject may quit the trial at any time
Illumination (or “illuminance”) – a light source. Scientifically, the amount of flux per unit area on a lighted surface.
Indocyanine [in-doe-SIGH-uh-neen] green angiography – photography of the retina using a green dye that fluoresces under ultraviolet light.
Infection – spreading of micro-organisms throughout bodily tissue or parts.
Infusion – introduction of fluid into the body by gravity through an intravenous (IV) tube.
Inheritance pattern – the way in which a gene or trait is passed through generations of a family.
Injection – introduction of fluid into the body by forced penetrance with a needle and syringe.
Intraocular – inside the eyeball.
Intravitreal – within the vitreous fluid of the eyeball.
Iris – the colored diaphragm in the anterior chamber of the eyeball which contracts and expands to adjust for light intensity. See Anatomy of the Eye.
Irradiate – to expose to radiation for diagnostic or therapeutic purposes.
J
Juxta- – next to, as in juxtaf oveal and juxtascleral.
L
Laser photocoagulation – an outpatient treatment whe rein blood vessels are cauterized by the heat from a fine-point laser beam.
Legal blindness – a standard of visual acuity set at 20/200 with correction in the better eye (see “Snellen Chart”) or a visual field of less than 20 degrees.
Lens – the transparent, dual-convex body at the front of the eye which focuses light rays onto the retina. See Anatomy of the Eye.
Linked – two or more markers that are close enough together on a chromosome to be inherited together.
Lipofuscin [LIP-oh-fuss-kin] – fatty deposits in the retina which are thought to be toxic to retinal cells. A by-product of drusen.
Low vision (or visually impaired) – significantly impaired vision which is not correctable with conventional devices.
Low vision devices – equipment designed to allow improved vision, usually by magnification.
Low vision rehabilitation – training for the visually impaired in adaptability and in the use of low vision devices, computer software and motility aids.
Low vision specialist – an optometrist who has been specially-trained in the examination, treatment, and management of patients with impaired vision.
Low vision therapist – a person who is certified to assist eye care specialists in providing training for vision impaired patients.
M
Macula [MACK-you-luh] (also “macula lutea,” or “yellow macula”) – the center of vision, containing mostly cone cells for detail, color, and daytime viewing. See Anatomy of the Eye.
Marker – a gene or DNA fragment with a known location on a chromosome that is associated with a certain disease. It can be used as a point of reference when looking for disease-causing mutations.
Melanin – the substance which gives color to the eyes and protects the macula by trapping light rays.
Membrane – a thin layer of tissue, which covers, surrounds, lines or separates parts of the body.
Migraine flashers – zigzag, shimmering, or even colorful lines that sometimes move within the visual field bilaterally. Thought to be caused by a sudden spasm of blood vessels in the brain.
Minimally classic – a type of wet AMD wherein the leaking blood vessels occupy half or less of the area of the entire lesion.
Mutation – a change in a gene.
Myopia (also “nearsightedness”) – a condition in which rays of light from distant objects are focused in front of the retina, causing blurred vision.
N
Nasal – toward the nose.
Neovascularization – growth of new, fragile blood vessels which may leak beneath the retina.
Non-optical devices – equipment used for supplementing or replacing vision, such as audio tape players, scanners, etc.
Nucleus – The central structure within the cell, which contains genetic material.
Nutraceutical – a natural food or supplement that is beneficial to health.
O
O&M – abbreviation for “Orientation & Mobility” training in the use of the white cane.
Optical Coherence Tomography (OCT) – A diagnostic method which uses an optical device to generate a cross-section image of the retinal layers, allowing for measurement of tissue thickness.
Ocular motility – movement of the eyes in relation to one another.
Occult CNV– The type of sub-foveal blood vessel presence in wet AAMD that has a source not readily defined.
OD – (oculus dexter) Latin abbreviation for “right eye.”
Ophthalmoscopy – examination of the internal structures of the eye using an illumination and magnification system.
Ophthalmologist [off-thall-mall-o-jist] – a practitioner in the medical science of surgery and care of the eye and its related structures. An M.D. degree is required.
Optic disc – the junction of all of the retinal nerve fibers at the beginning of the optic nerve. Appears as a grayish disc shape near the fovea in fundus photos. See Anatomy of the Eye.
Optic nerve – transmits neural impulses from the retinal cell layers to the brain. See Anatomy of the Eye.
Optician – a person who designs or manufactures ophthalmic appliances or optical instruments (“ophthalmic optician”) or deals in prescriptions (“dispensing optician”).
Optometrist – an independent, primary health care provider who is skilled in the co-management of eye health and vision care, to include examination, diagnosis, treatment, management of diseases and disorders, prescription of eyeglasses and contact lenses, and provision of low vision aids and vision therapy. An O.D. degree is required.
OS – (oculus sinister) Latin abbreviation for “left eye.”
OU – (oculi uniter, or unitas) Latin abbreviation meaning both eyes working simultaneously as a unit.
Oxidation – loss of electrons from molecules in healthy cells, caused by free radicals and leading to loss of vision.
P
Pathological – caused by or having to do with a disease.
Pedigree – a multigenerational family tree using symbols to denote lineage and genetic information.
Peripheral vision – the outer part of the field of vision made possible by the rod cells.
Pharmaceutical – a substance, such as a drug or medicine, used in medical treatment.
Photodynamic therapy (PDT) – the process of blood vessel coagulation in the retina through activation of a light-sensitive drug injected into the system.
Photophobia – sensitivity to light.
Photoreceptor – a cell in the retina which converts light into nerve impulses. See Anatomy of the Eye.
Pigment Epithelial Detachment (PED) – separation of the retinal pigment epithelial (RPE) layer from the photoreceptor cell layer, resulting from fluid buildup.
Placebo – an inactive substance which has no effect on the body.
Pluripotent – stem cells which have the potential to develop into a number of different cell types, such as red blood cells, platelets, or lymphocytes.
Polarization – a process whereby a chemical film is applied to glass to reduce horizontal glare (i.e. reflection off of water or roadways).
Posterior – behind, or the back surface.
Posterior Vitreous Detachment (PVD) – a condition in which the vitreous humour (gel) separates from the retina.
Predominantly classic CNV – a type of wet AMD wherein the leaking vessels are well-defined.
Preferred retinal locus (PRL) – the favored fixation point for viewing an image.
Prosthesis – an artificial device which replaces a missing part of the body.
Proteins – large organic molecules that are made up of all of the basic substances of the body.
Pupil – the opening at the front of the eye in the center of the iris, through which light passes. See Anatomy of the Eye.
R
Reduced penetrance – a gene whose effect has been modified or reduced.
Retinal cell layers – The membrane on the inner wall of the eyeball which receives the image from the lens and converts it into neural impulses. See Anatomy of the Eye.
Retinal Pigment Epithelium (RPE) – The layer of the retina lying between the blood vessels and the photoreceptor cell layer. See Anatomy of the Eye.
Retinal specialist – a medical doctor who specializes in diseases such as retinal detachments, advanced diabetic retinopathy, and some forms of macular degeneration.
RNA (ribonucleic acid) – a molecule, similar to DNA, which carries information into the cell from DNA to synthesize proteins.
Rod cells – the photoreceptor cells in the retina which are responsible for peripheral and night vision (scotopic Focal Points). See Anatomy of the Eye.
Ruyschian [ROY-she-an] membrane – a network of capillaries in the choroid which supplies the outer five retinal layers. This network is most dense at the macula.
S
Scanning laser ophthalmo scopy (SLO) – a device for photographing the retina, wherein a quickly scanning low intensity laser sends images to a computer monitor.
Sclera – the white, dense, fibrous outer coating of the eyeball. See Anatomy of the Eye.
Scleral buckle – a surgical procedure for high myopes which inhibits further stretching of the eyeball.
Scotoma – a blind spot, or area of diminished sensitivity in the visual field.
Scotopic vision – night vision
Sex Chromosome – an X or Y chromosome. The XX pair determines female, and the XY pair determines male.
Sham – a fake treatment or drug administered to the control group in a experimental study.
Slit lamp – an instrument with a light source that is focused into a slit for use, in combination with a biomicroscope, in examining the frontal structures of the eye.
Snellen visual acuity chart – the standard tool for the measurement of visual acuity, displaying letters of progressively smaller size.
Statin – a type of cholesterol-reducing drug that lower the levels of fats (lipids) in the blood
Stem cells – undeveloped structures which are able develop into any of the nearly 220 cell types that make up the human body, and which can theoretically reproduce themselves infinitely.
Stereopsis – the capability of depth perception in both eyes.
Subcutaneous – beneath the skin.
Subfoveal – beneath the fovea.
Surgical – a medical procedure involving an incision or laser procedure.
Symptomatic – displaying symptoms
Syndrome – a group of symptoms that identify a particular disease or condition.
T
Tangent screen test – an examination during which the patient identifies a spot of light moving into his peripheral field.
Tear film – the clear saline fluid which cleanses and lubricates the front surface of the eye.
Temporal – toward the ear.
U
Ultrasonography (ultrasound) – the use of sound waves to examine the eye and surrounding area for analysis of tumors, retinal detachments, or cataracts.
Ultraviolet (UV) – light wavelengths which are shorter than the violet end of the visible spectrum and longer than the roentgen radiations.
V
Variable expressivity – a gene whose effect varies from one person to the next.
VEGF (Vascular Endothelial Growth Factor) – a protein that is responsible for blood vessel development (angiogenesis).
VIP – Visually Impaired Person
Vitreous gel (humour) – A clear jelly-like substance which fills the posterior chamber of the eyeball.