Glossary of Retinal Degenerative Disease Research
Angiogenesis: Refers to the growth of new blood vessels. When uncontrolled, angiogenesis can cause destruction of the retina due to leakage or cause accelerated growth of a tumor in certain cancers. Angiogenesis is associated with the wet form of age-related macular degeneration, where it is thought that blood vessels grow from the choroid (vessels behind the retina) through the Bruch’s membrane (blood-retina barrier) and leak blood into the retina where RPE and photoreceptor cells reside.
Antioxidant: Is a substance that protects a cell from damage that may occur from light, stress, or metabolic processes (called oxidation). Some well-known antioxidants include compounds normally present in food such as, vitamin E, beta-carotene, lutein and zeaxanthin, and vitamin C. If you do take nutritional supplementation, please consult yearly with your personal physician and ophthalmologist for monitoring.
Apoptosis or Programmed Cell Death: A genetically-controlled process that causes degenerating photoreceptor cells (or any other cell type) to die. Apoptosis is common to all retinal degenerative diseases. Scientists don’t know exactly how this process is triggered, but it is hoped that an understanding of apoptosis will lead to sight-saving therapies that prevent or delay photoreceptor cell death.
AREDS (Age-Related Eye Disease Study): A specific nutritional supplementation regimen approved by the FDA for prolonging retention of vision in individuals with AMD. The AREDS supplementation is: Antioxidants (500 mg Vitamin C, 400 IU Vitamin E, 15 mg Beta-carotene) and Minerals (80 mg Zinc Oxide, 2mg Copper). If you do take nutritional supplementation, please consult yearly with your personal physician and ophthalmologist for monitoring.
Autosomal Dominant Disease: The affected person has one altered/mutated gene paired with one normal gene. These genes lie on one of the 22 pairs of autosomal chromosomes [the non-sex chromosomes (X or Y); see autosome below] that are inherited from parents.  A larger number of identified disease-causing genes are from dominant diseases, since there is normally an affected person in every generation.
Autosomal Recessive Disease: The affected person needs to have both copies of the gene altered. These genes lie on one of 22 pairs of autosomal chromosomes [the non-sex chromosomes (X or Y); see autosome below] that are inherited from parents. The double-inheritance of the same recessive gene mutation occurs less frequently than inheritance of a dominant disease gene mutation (and there isn’t necessarily an affected person in every generation), making it more difficult to identify recessive disease-causing genes.
Autosome:  A chromosome (how our DNA is packaged) that is not a sex chromosome (X or Y). Autosomal recessive and autosomal dominant diseases are caused by mutations in genes that reside on one of the 22 paired autosomes.
Axokine: A survival factor. Axokine is a genetically altered form of the survival factor known as ciliary neurotrophic factor (CNTF). Survival factors are naturally-occurring substances that promote the health of nerve cells such as photoreceptors. Axokine has delayed retinal degeneration in a variety of animal models with retinal degeneration.
Beta-carotene: A nutritional pigment found in certain orange vegetables, like carrots, that is an anti-oxidant. Chemically, this pigment is like two vitamin As connected together that needs to be processed by the body to “disconnect” them. Beta-carotene (15 mg) is one component of the FDA-approved AREDS daily nutritional supplementation for treatment to prevent progression of vision loss in AMD. It’s important to note that beta-carotene can be taken as a nutritional supplement for those with AMD, but is thought to be damaging to those who have RP (where it has been clinically-tested that instead, 15,000 IU of vitamin A palmitate can help prolong vision retention). This is a good demonstration that the same nutritional supplementation is not good for all retinal degenerative diseases. If you do take nutritional supplementation, please consult yearly with your personal physician and ophthalmologist for monitoring.
Bruch’s membrane: The blood-retina barrier that separates the RPE cells from the choroid. It is synonymous with the blood-brain barrier because the eyes are extensions of the brain. A rupture of this barrier can cause diseases, like AMD, where the choroid blood vessels grow through into the retina and cause damage, ultimately affecting vision.
Cell: The smallest biological unit of specialized function capable of self-replication. A cell consists of an outer membrane (like a porous plastic bag), which encases the fluid of the cell, and the nucleus, a specialized compartment that contains the DNA and directs the production of proteins. Many cells put together can form an organ, like the retina or the brain.
Cell Based Therapy: One of The Foundation’s six research priority areas. Scientists and clinicians are testing treatments for retinal degenerative diseases with stem cell replacement and retinal transplants. This therapy has potential to treat all retinal degenerative diseases, even in those people who have completely lost all photoreceptor and/or RPE cells.
Cellular and Molecular Mechanisms of Disease: One of The Foundation’s six research priority areas. Scientists and clinicians are determining how mutations in each identified gene cause retinal degenerative disease and specifically what goes wrong in the cells of the eye as a result of this mutation.
Central Nervous System: The “central command” of the body, including the brain and retina. Every nerve cell outside of the blood-brain and the blood-retina barrier is considered part of the peripheral nervous system.
Choroid: The layer of cells that sits just below the retinal pigment epithelial (RPE) cells. The choroid is rich in blood vessels, and is a major supplier of oxygen and nutrients to the RPE and photoreceptor cells. It also takes away the waste from these cells.
Chromosome: One of the "packages" of genes in the nucleus of a cell. A chromosome is mainly composed of DNA. Humans have 23 pairs of chromosomes (22 pairs of autosomes and one pair of sex chromosomes). Each parent contributes one chromosome to each child, so children inherit half of their chromosomes from their mothers and half from their father. This is important to understand when one tries to understand the difference between recessive, dominant and X-linked inherited retinal degenerative diseases (see individual definitions).
Ciliary Body: A part of the eye near the iris that contains the “strings” that control the thickness of the lens, thus making adjustments to the “focus” and how light falls onto the retina.
Cone Cell: A type of photoreceptor cell that detects light. Although cones are present throughout the retina, they are mainly found in the macula (the central portion of the retina). Cone cells are particularly important for color and day vision and discriminating fine visual detail, like that required for driving a car or reading a book. There are three types of cone cells (blue, green and red) that respond to different wavelengths of light to make up the full rainbow of colors.
Copper: A mineral that is required for nutrition and proper function and maintenance of the body. Copper (2 mg) is one component of the FDA-approved AREDS daily nutritional supplementation for treatment to prevent progression of vision loss in AMD. Copper was added to the AREDS formulation to prevent potential unwanted damage from too much zinc oxide supplementation. If you do take nutritional supplementation, please consult yearly with your personal physician and ophthalmologist for monitoring.
Cornea: The clear dome that covers the front of the eye. It lets in light and starts to focus it onto the lens. If the eye is like a camera, consider this to be like a UV (ultraviolet) filter screwed onto the end of a camera lens. This is the part of the eye that undergoes vision-correcting LASIK (Laser-Assisted In Situ Keratomileusis) surgery.
Cortical Implant: A chip/cable implanted in the visual cortex, the specific portion of the brain found at the back of the head that interprets visual information. This chip device would theoretically transmit visual images from camera-like sunglasses directly to the brain. The goal of this device is similar to the retinal chip and could possibly restore vision to patients who are completely blind or to those who don’t have a functioning optic nerve.
Cortical Implant: A microelectrode chip implanted in the visual cortex, the portion of the brain that interprets visual information. This device would theoretically transmit visual images from a camera-like device to the brain. The goal of this device is similar to the retinal chip and could possibly restore ambulatory vision to patients with end-stage retinal degeneration.
DHA (docosahexaenoic acid): A highly unsaturated fatty acid (a type of omega-3 fatty acid) that is greatly concentrated in rod photoreceptor cells. Foundation-supported scientists have found that patients with some forms of RP and Usher syndrome have lowered serum levels of DHA. A clinical trial is currently in progress to test whether DHA used as a nutritional supplement can slow the progression of X-linked RP, Usher syndrome and Age-related macular degeneration. If you do take nutritional supplementation, please consult yearly with your personal physician and ophthalmologist for monitoring.
DNA: The long chain of building-blocks that carries the genetic instructions (genes) for making living organisms. Each DNA building-block can be thought of as a “letter,” and when there’s a gene mutation (or “spelling mistake” for even one letter) it can create a non-functioning protein and disease may be the result. DNA is found in the nucleus of a cell where it is organized into highly specific sequences that define each gene on the 23 chromosomes. Each gene makes a messenger called RNA, which then is the template for making proteins, the actual work-horses of the cell.
Dominant: see Autosomal Dominant Disease
Drusen: Yellow-white deposits found under the macula. Drusen deposits are associated with the dry form of Age-related macular degeneration (AMD) and with some juvenile forms of macular degeneration, like Best disease and Stargardt disease. They are thought to be an accumulation of waste materials, including fats and proteins. Scientists are still determining their composition and why they help to promote disease.
Free Radical: A molecule that can cause oxidative damage to a cell or tissue. Antioxidants are used to destroy free radicals.
Gene: An organized sequence of molecules that "spells out" the information necessary to construct a specific messenger called "messenger RNA" which, in turn, makes a specific protein. Every cell has the same genetic make-up; however, different genes are turned on in different cells. These genes act as blueprints to produce a highly specialized combination of proteins that are essential to the cell's function and specialty. For example, the genes ROM-1 and peripherin are important in forming the outer segment membranes of photoreceptor cells. Other proteins, like rhodopsin, are involved in a rod cell's response to light.
Gene Mapping: The process of identifying a specific region (or locus) along one of the 23 paired chromosomes that contain a gene with a disease-causing mutation. Also known scientifically as "positional cloning". Once scientists have narrowed down the possibility to a particular locus on the chromosome, then they can identify the gene linked with the disease.
Gene Therapy: One of The Foundation’s six research priority areas. The delivery of a gene or genetic information into cells for the purpose of achieving a therapeutic effect. In other words, it’s replacing the “bad” or mutated gene with the “good” or non-mutated, functioning gene (the gene mutation or “spelling mistake” has been corrected). Three forms of gene therapy (gene replacement therapy, ribozyme therapy and RNAi) have shown promise in the treatment of retinal degenerative diseases. Gene replacement therapy is replacing the “bad” gene with the “good” form, ribozyme therapy chews-up the “bad” RNA (the gene messenger) so that it can’t make a “bad” protein that will do harm and RNAi treatment causes the “bad” RNA to be destroyed by existing cell defense processes.
Genetics: One of The Foundation’s six research priority areas. Scientists and clinicians are looking for new genes linked to retinal degenerative diseases. It is thought that only approximately half of disease-causing genes have already been identified.
Genotyping: The process of screening patients’ DNA to identify the specific gene and the specific mutation (spelling mistake) in a gene that causes a disease. The DNA samples are normally obtained by collecting a blood sample (since all cells of the body have the same genetic code). For more information on genotyping and how you can be tested, please obtain a copy of The Foundation’s Genetic Testing Information Packet. Scientists are attempting to connect the genotype with the phenotype for every disease.
Iris: The colored ring “surrounding” the pupil that regulates the amount of light that is admitted into the eye. If the eye is like a camera, consider this to be the aperture.
Lancelot: A briard dog born blind with a mutation in the RPE65 gene, causing a dog-form of the human retinal degenerative disease called Leber’s Congenital Amaurosis (LCA). As reported in 2001, researchers injected into the retina of one of Lancelot’s eyes a “good” copy of the RPE65 gene that corrected his vision in that one eye. Since Lancelot’s treatment, over 50 dogs have been treated in a similar manner and can now see. A human clinical trial based upon this research will begin in 2006.
Lens: The oval-shaped, clear part of the eye behind the cornea and iris that focuses incoming light onto the retina. If the eye is like a camera, consider this to be like a camera lens.
Locus/Loci: A location in one part of a chromosome where a particular gene might reside, like a “house” might reside in a “neighborhood.” Scientists who are looking for genes associated with retinal degenerative diseases call it a locus until they definitively prove that one gene in this region causes the disease.
Lucentis: A drug approved by the FDA in June 2006 for treatment of wet AMD. It is an anti-VEGF drug, a fragment of a VEGF antibody that binds to and blocks the parts of VEGF protein that promote vessel growth and leakiness. This reduces the pockets of blood in the retina, allowing not only 90-95% of those treated to not lose 3 lines on a visual acuity chart one year after treatment, but also helps approximately one-third of treated individuals to improve 3 lines of vision.
Lutein and Zeaxanthin: Anti-oxidant nutrient pigments that are abundant in green leafy vegetables and yellow and orange fruits and vegetables. These pigmented carotenoids (another word used for lutein and zeaxanthin) are highly concentrated around the macula and give the macula its characteristic yellow appearance. Lutein and zeaxanthin are thought to protect the macula from oxidative stress due to ultraviolet light exposure. If you do take nutritional supplementation, please consult yearly with your personal physician and ophthalmologist for monitoring.
Macugen: The anti-VEGF drug approved by the FDA in 2004 for treatment of wet AMD. This drug “sticks” together VEGF proteins, making them inactive. This was the first approved anti-VEGF drug for treatment of a retinal degenerative disease and showed a dramatic increase of retention of vision (70-75% don’t lose 3 lines on a visual acuity chart one year after treatment) versus people who are untreated (50%). However, Lucentis (approved in June 2006) has been shown to have more dramatic improvement in treatment of AMD (90-95%).
Macula: The central portion of the retina. The macula contains a dense concentration of cone photoreceptor cells that help us see fine visual detail and color vision. Only primates (humans and monkeys) have maculas.
Macular Translocation Surgery: An experimental surgical procedure for the wet form of AMD. In this procedure, surgeons detach the retina and then relocate the macula to rest on healthy tissue, away from the area of abnormal blood vessel growth that causes vision loss.
Metabolic process: The body chemically breaks down nutrients and converts them into simple energy packets that the body can use for maintenance, movement and other functions. Oxidation is one of these processes and anti-oxidants help to control damage from too much oxidation.
Mutation: A truncation or change in the normal order or “spelling mistake” of DNA that defines a specific gene. A disease-causing mutation in a gene alters the gene blueprint/template and thus ultimately disrupts the construction and/or activity of the resulting protein.
Neuroprotective Therapy: One of The Foundation’s six research priority areas. Scientists and clinicians are testing delivery of survival proteins or drugs to protect the photoreceptors from dying (or losing their light-detection ability). This is an especially important priority area, since survival proteins or drugs could potentially treat all retinal degenerative diseases.
Nucleus: The specialized compartment within every cell that contains DNA. This is also the location where RNA (messenger RNA) is made from genes and transported out of the nucleus to be a template for protein production.
Nutritional and Environmental Therapy: One of The Foundation’s six research priority areas. Scientists and clinicians are using nutritional supplementation that has been clinically proven to slow or stop the loss of vision in some retinal degenerative diseases, like RP and AMD. If you do take nutritional supplementation, please consult yearly with your personal physician and ophthalmologist for monitoring.
Omega-3 fatty acid: see DHA. This is a type of fat that is important for cell processes. The term “omega” refers to the specific configuration of chemical “double-bonds” and thus predicts the shape of the fat. Omega-3 is found in many different sources, including some fish and nuts. AREDS II is a clinical trial which will begin in 2006 that will test whether supplementation of omega-3 fatty acids, lutein and zeaxanthin can add to the clinical effect of the already-approved AREDS supplementation (a specific combination of antioxidants and minerals). If you do take nutritional supplementation, please consult yearly with your personal physician and ophthalmologist for monitoring.
Optic Nerve: The “cable” that takes the signals of light detection from the retina and transports them to the part of the brain called the visual cortex. If the eye is a digital camera, consider this to be like the cable used to download the images onto a computer. The photoreceptors “detect” the photons of light and convert them into chemical and then electrical signals that are sent over the optic nerve “cable.” A person doesn’t actually “see” until their visual cortex processes the signals.
Oxidative Stress/Oxidation: A process whereby the metabolic balance of a cell is disrupted by exposure to environmental substances resulting in accumulation of free-radicals, which can damage the cell. It is thought that anti-oxidants can protect a cell from this damage.
Peripheral Nervous System: Not the brain or retina. Normally these are the nerves that control moveable muscles (and other voluntary, controllable processes done by individuals) or are the nerves involved in the involuntary processes, like breathing, heart rate, etc.
Phenotype: The observable characteristics or clinical symptoms present in an individual with a particular retinal degenerative disease. Scientists are attempting to correlate the phenotype with the genotype for every retinal degenerative disease.
Photodynamic Therapy: A new therapy for the wet form of AMD. This therapy consists of a light-activated drug (e.g. Visudyne) injected into the patient's bloodstream that preferentially collects in areas of new blood vessel growth (angiogenesis). Once this drug is administered, a surgeon aims a low-intensity or "cool" laser at the area of blood vessel growth. The laser activates the drug, which then destroys the leaky blood vessels. Since the drug is confined within the blood vessel, the laser treatment mainly targets the vessel and does not harm the overlying retinal tissue. It is thought that photodynamic therapy may offer patients with wet AMD a safer, more effective sight-saving therapy than traditional laser treatment. However, there are newer anti-VEGF drugs, called Macugen and Lucentis, that have been reported to cause better retention of vision one year after treatment.
Photoreceptor Cells: The light sensitive cells in the retina that absorb light and convert it into an electrical signal that is passed to the brain through the optic nerve (see phototransduction). There are two types of photoreceptor cells: rod and cone cells. Rod cells are responsible for black-and-white, peripheral and night vision. Cone cells are mainly responsible for color, central and day vision. There are three types of cone cells, red, green and blue, that detect color light of different wavelengths. In humans, rod cells are more numerous in the periphery while cone cells are concentrated in the central portion of the retina (macula). The toxins produced by the chemical conversion of light to an electrical signal are detoxified and/or recycled by the adjacent RPE cells.
Phototransduction: Also called the visual cycle. The cascade of biochemical reactions involved in detecting light and converting it to an electrical signal that is relayed to the brain via the optic nerve. Both photoreceptors and RPE cells are essential for this process.
Proof of Principle: Scientific confirmation that a previously unproven idea or experimental therapy actually confers a therapeutic effect in animal models. Proof of principle provides the first measurable evidence that an experimental therapy might also work in humans.
Recessive: see Autosomal Recessive Disease
Retina: The retina contains the light-detecting cells in the back of the eye. If the eye is a camera, consider the retina to be like the film or digital sensor. The retina contains several nerve cell types that are similar to brain cells since it is an extension of the brain, and thus part of the Central Nervous System. The cell types that are considered part of the retina include photoreceptor nerve cells (rods and cones) and other types of nerve cells that relay the signal to the optic nerve “cable” (horizontal, bipolar, amacrine, ganglion, Müller cells) as well as retinal vessels, RPE cells, and Bruch’s membrane. The photoreceptor cells of the retina absorb light and convert this light to electrical signals (also called phototransduction). The electrical signals are transferred from the photoreceptors to other, secondary nerve cells which then send the electrical signals to the optic nerve, then the visual cortex region of the brain for interpretation.
Retinal Cell Transplantation: Transplanting a layer of cells (already composed of photoreceptor and RPE cells) into the retina, near the macula. There are two ways that retinal transplantation could improve vision: 1) The transplanted, healthy photoreceptor and RPE cells would integrate into existing retina and signal through the optic nerve to the brain; 2) The transplants would slow or stop the progression of the disease by producing survival factors that would keep remaining photoreceptor cells from dying and improve their detection of light and transmission of signals (transplants wouldn’t integrate into the retina). Clinical trials are currently underway.
Retinal Chip: (also called Artificial Retina or Retinal Prosthesis) A computer chip designed to mimic basic photoreceptor cell function. Such a device, implanted on the surface of the retina, could possibly restore vision to patients with end-stage retinal degeneration. It works similar to a digital sensor found in the back of a digital camera.
Retinal Pigment Epithelium (RPE): A very thin, pigmented cell layer directly beneath the retina. RPE cells lie between the photoreceptor cell layer of the retina and the Bruch’s membrane and choroid. The RPE obtains nutrients and oxygen from the choroid and provides these to the photoreceptor cells. It also carries waste products from photoreceptor cells for disposal to the choroid. The RPE recycles proteins and other component involved in the phototransduction process and provides other survival factors to the retina.
Retinal Prosthesis: also Artificial Retina or Retinal Chip: A computer chip designed to mimic basic photoreceptor cell function. Such a device, implanted on the surface of the retina, could possibly restore ambulatory vision to patients with end-stage retinal degeneration.
Retinal Vessels: The vessels found on top of the retina that look like “tree branches” when viewed by an ophthalmologist when they shine a light onto the back of the eye. These vessels become damaged during eye diseases like diabetic retinopathy, retinopathy of prematurity and other diseases.
Rhodopsin: Rhodopsin is formed when a protein called opsin is chemically linked to a specialized/processed form of vitamin A. Rhodopsin resides almost exclusively in the outer segments of rod photoreceptor cells (near the RPE cells) and can only be formed in the dark. When light strikes, the rhodopsin molecule changes shape, generating the initial signal in the visual process. Ultimately, the specialized vitamin A splits off from the opsin protein to be recycled by the RPE cells and brought back to the photoreceptor outer segments, where it can be reattached to opsin in the dark. This series of reactions in light and dark is called the visual cycle (or phototransduction).
Ribozyme Therapy: A form of gene therapy normally used for for autosomal dominant forms of retinal degeneration. In autosomal dominant disease, patients have one healthy functioning gene and one gene with a disease-causing mutation. The mutant gene produces a dysfunctional protein that damages the photoreceptor cell. Ribozymes disrupt specifically the mutant gene's ability to produce the harmful protein, by “chewing-up” the gene’s RNA messengers. The healthy functioning gene would not be affected, and therefore there is still enough “good” protein to stop the disease and hopefully restore vision.
RNA: Also known as mRNA. The “messenger” (hence calling it mRNA) from a gene that becomes the template for making protein. Scientists and clinicians are currently testing mRNA targeting in many treatments for retinal degenerative diseases.
RNAi Therapy: A short piece of gene “sequence” or “letters” that when injected into the eye, can interact with native RNA and mark them for destruction. This method is useful for destroying RNA from mutated genes, to prevent production of non-functioning proteins. Scientists and clinicians are currently testing combinations of RNAi therapy with gene therapy to also replace the “bad” with the “good,” or functioning, gene.
Rod Cell: A type of photoreceptor cell that is located throughout the retina but is more common outside of the central macular region of the retina, i.e. the periphery of the retina. The rod cell is particularly important for night vision, black and white vision, and side or peripheral vision. In many forms of RP, rod cell loss leads to loss of peripheral vision (i.e., causing tunnel vision).
Sclera: The “whites of the eyes” that is a tough outer protective shell. If the eye is like a camera, consider it to be like the camera body.
Sex Chromosomes: These are the X and Y chromosomes inherited from a mother and father. The inherited combination of X and Y chromosomes determine the sex of the baby. A female/woman inherits two X chromosomes (one from each parent) and a male/man inherits only one X chromosome from his mother and one Y chromosome from his father. There are some genes on the X chromosome that, when mutated, will cause particular types of retinal degenerative diseases. Therefore the man normally is symptomatic and the woman is a carrier.
Stem Cell: A primitive, unspecialized cell that has the capacity to self-regenerate but develop a highly specialized function when grown in the appropriate environment and treated with specific proteins or survival factors. In other words, it’s a cell that “hasn’t decided what it wants to be when it grows up.” Stem cells for the retina have been found in the ciliary body, a specialized structure that sits on either side of the iris, near the retina. They usually lie dormant in the adult. Stem cells have now been isolated and are being evaluated as a potential source for RPE and photoreceptor cells for transplants.
Stem Cell: A primitive, unspecialized cell that has the capacity to develop highly specialized function when grown in the appropriate environment and treated with specific growth factors. Stem cells for the retina reside in the ciliary body, a specialized structure that sits on either side of the iris, near the retina. They usually lie dormant in the adult. Stem cells have now been isolated and are being evaluated as a potential source for RPE and photoreceptor cells for transplants.
Survival Factors:  See Neuroprotective Therapy. Naturally-occurring proteins or drugs that promote the health of nerve cells such as photoreceptors. There are many different types of survival factors. Examples include, ciliary neurotrophic factor (CNTF), pigment epithelium-derived factor (PEDF), basic fibroblast growth factor (bFGF) and glial-derived neurotrophic factor (GDNF). Ciliary neurotrophic factor (CNTF) is a survival factor that is currently being used in clinical trials for RP and AMD. Gene therapy (for the RPE65 gene) for Leber’s Congenital Amaurosis is rapidly approaching clinical trials.
Trans Fats: see Unsaturated fatty acid
Transpupillary Thermotherapy (TTT):  A treatment of the wet form of age-related macular degeneration, specifically in patients with a condition called occult choroidal neovascularization where blood vessel growth is hidden. The procedure involves using a low-intensity laser to apply heat to the area of new blood vessel growth. The slightly elevated temperature then stops the leakage of blood vessels and reduces the size of lesions in that area. Although preliminary studies were promising, further research is needed to refine this process. In addition, there are newer treatments like the anti-VEGF drugs Macugen and Lucentis which may have more beneficial results, depending on the individual’s clinical condition.
Ultraviolet (UV) light: UV light is part of the light/radiation that comes from the sun, with a wavelength shorter than that of visible light, but longer than soft X-rays. There are approximately three types of UV light: UVA (400–315 nm), also called Long Wave or "blacklight"; UVB (315–280 nm), also called Medium Wave; and UVC (< 280 nm), also called Short Wave or "germicidal" (because it can destroy DNA). To protect your eyes, it is recommended that you wear sunglasses that have protection against all forms of UV light. This is particularly important for those who have retinal degenerative diseases, because their retina may be extra-susceptible to damage or vision loss from exposure to UV light (depending on the nature of their disease).
Unsaturated fatty acid: A fat that has one or more chemical “double bonds” between the carbons of the fat “backbone.” Hydrogen molecules that are part of double bonds may be in a cis or trans position. The cis conformation hydrogens are on the same side of the double bond, whereas in the trans conformation they are on the opposite side. Trans fats are popular with manufacturers of processed foods because they are less vulnerable to rancidity and are more solid at room temperature than cis fat. But trans fats reduce the fluidity (and functionality) of cell membranes. A number of studies have linked trans fats to a risk of developing AMD.
Vector:  The vehicle for delivering genes or genetic information into the nucleus of a cell. Vectors act like a fleet of microscopic delivery trucks transporting new, therapeutic genes into retinal cells. Most vectors are modified forms of viruses (a “safe” form). Viruses are extremely effective at getting inside a cell. However, viruses also contain elements that may damage cells. Over the past decade, researchers have been working to genetically modify viruses to be safe and have few immune side effects, without compromising their delivery capabilities. Examples of vectors include lentiviral vectors, adeno-associated vectors (AAV), and encapsidated adenovirus minichromosome (EAM). The upcoming clinical trials for LCA with RPE65 Gene Therapy uses a retina-specific AAV vector.
VEGF (Vascular Endothelial Growth Factor): A class of proteins that cause blood vessel growth (angiogenesis) and leakiness, which are needed for normal body functions, like development, wound repair and women’s monthly menstrual cycle. It is thought that abnormally-high levels of VEGF (or its presence in places where it shouldn’t be expressed) causes disease. Several anti-VEGF targeting/treatments are being used for treatment of wet AMD (as well as several other diseases that have unwanted blood vessel growth, like colon cancer).
Visual Cycle: Where light is converted in the retina to an electrical signal that is sent down the optic nerve to be processed in the brain. See Phototransduction above.
Vitamin C: A water-soluble anti-oxidant found abundantly in certain fruits and vegetables, like citrus fruits, tomatoes and potatoes. Another name for vitamin C is ascorbic acid. Vitamin C (500 mg) is one component of the FDA-approved AREDS daily nutritional supplementation for treatment to prevent progression of vision loss in AMD. If you do take nutritional supplementation, please consult yearly with your personal physician and ophthalmologist for monitoring.
Vitamin E: A fat-soluble anti-oxidant found in vegetable oils, nuts, olives and other foods. Vitamin E (400 IU) is one component of the FDA-approved AREDS daily nutritional supplementation for treatment to prevent progression of vision loss in AMD. If you do take nutritional supplementation, please consult yearly with your personal physician and ophthalmologist for monitoring.
Vitreous: The clear, jelly-like substance found in the middle of the eye that helps to regulate eye pressure and shape. Light must pass through the vitreous to fall upon the retina, so it must be as transparent as possible to avoid vision distortion or disruption.
Wavelength: Light is made of many bundles of energy that are either visible or non-visible by humans that tends to travel in a “wave” pattern. A wavelength (measured in nanometers) is the distance between the repeating units of the wave and frequency (measured in Hertz; 1 Hz means it repeats once per second) is the number of times that unit repeats over a unit of time. Light with a shorter wavelength tends to be traveling at a faster frequency. Only light that travels in the visual spectrum, between 400-700 nm (or ~1015 Hz), is seen by the unaided eye. At one end of the electromagnetic spectrum is Gamma-Rays (short and fast: 124 pm or 1018 Hz) and at the other end is Radio Frequency, like that used by submarines (long and slow: 100,000 km or 3-30 Hz) or FM radio or television broadcasts (1-10 m or 30–300 MHz). The photoreceptor cell converts light from the visible range into chemical, then electrical energies that travel via the optic nerve to the visual cortex in the brain, where the signals are processed.
X-chromosome:  Of the 23 pairs of chromosomes that humans carry in each cell of their body, genes on a single pair of chromosomes (called X and Y) determine the gender of the baby. A female/woman is only capable of transmitting the X chromosome to her offspring since females always have two X chromosomes (XX), while males/men can transmit either an X or a Y chromosome to an offspring since males always have one X and one Y chromosome (XY). Importantly, the X- chromosome also contains many other genes that have nothing to do with determination of gender. Mutations in these genes on the X-chromosome result in diseases that are transmitted to male offspring (who have a single X-chromosome) through the maternal line. These are called X-linked diseases. Females can be carriers of the mutated genes but seldom show signs of the disease since they bear another X chromosome that does not have the same mutation and thus produces a normal protein.
Y-chromosome: The sex chromosome passed-down from father to son that contains genetic instructions to give men their body characteristics (amongst other functions). Males inherit one Y chromosome from their father and one X chromosome from their mother, therefore are normally symptomatic if they have an X-linked disease. So far, there are no known retinal degenerative diseases linked to the Y chromosome.
Zeaxanthin and Lutein: See Lutein and Zeaxanthin above
Zinc: A mineral that is required for nutrition and proper function and maintenance of the body. Zinc oxide (80 mg) is one component of the FDA-approved AREDS daily nutritional supplementation for treatment to prevent progression of vision loss in AMD. If you do take nutritional supplementation, please consult yearly with your personal physician and ophthalmologist for monitoring.