Glossary

achromatopsia

Achromatopsia is a type of cone dystrophy where there are normally problems only with vision from cone photoreceptors, the ones responsible for color and day vision and visual acuity. Therefore individuals mainly see by their rod cells, may be completely colorblind or almost colorblind, and have poor visual acuity. They also may have a variable degree of nystagmus (involuntary movement of the eyes). Other types of cone dystrophies may involve some degree of loss of rod cell vision.

adult stem cell

see stem cell

see AREDS

amd

see age-related macular degeneration

angiogenesis

The growth of new blood vessels. When growing in places they shouldn’t, they can cause disease, such as wet age-related macular degeneration (AMD). Angiogenesis refers to the growth of new blood vessels. When uncontrolled, angiogenesis can cause destruction of the retina due to leakage of blood.

antioxidant

A nutritional supplement (like vitamins C or E), drug, or naturally occurring product that protects cells from damage induced by light, stress or metabolic processes (called oxidation). Antioxidants are also prevalent in foods, such as vegetables and fruits.

apoptosis or programmed cell death

A controlled process for cell death, triggered by a signal or biochemical reaction, in response to an accumulation of cellular damage.

AREDS was a clinical study sponsored by the Federal government’s National Eye Institute that determined a specific nutritional supplementation regimen for slowing progress of vision loss 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). Another study-AREDS II, started in October 2006-is designed to test modified minor adjustments to the original supplement combinations (e.g., removing beta-carotene from the formulation, lowering zinc), along with different dosages of lutein, zeaxanthin and/or omega-3 fatty acids. If you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring or a non-typical approach and nutritional supplements may interfere with prescribed medicines.

autosomal dominant disease

Disease caused when an individual inherits a disease-causing mutation in one copy of a gene pair.

autosomal recessive disease

Disease caused when an individual inherits a mutation(s) that may not cause disease unless both copies of a gene pair are mutated.

autosome

Any chromosome within the 22 pairs of non-sex (not X or Y) chromosomes inherited by every individual from their biological parents.

An autosome is a chromosome (or DNA package) that does not play a primary role in determining a person’s sex (i.e., not an X or Y chromosome). Autosomal recessive and autosomal dominant diseases are caused by mutations in genes that reside on one of the 22 paired autosomes.

bardet-biedl syndrome (bbs)

Bardet-Biedl syndrome is a complex disorder that affects many parts of the body including the retina. Individuals with BBS have a retinal degeneration similar to retinitis pigmentosa (RP).

bbs

see bardet-biedl syndrome

best disease

Best disease is an inherited form of juvenile macular degeneration characterized by a loss of central vision.

beta-carotene

A nutritional pigment (and antioxidant) that can be used in the visual cycle of the eye. It is responsible for the orange color of carrots and other fruits and vegetables.

bruch's membrane

The blood-retina barrier that separates the retina from the rest of the body, that is often broken in individuals with wet AMD.

The Bruch’s membrane is the blood-retina barrier that separates the RPE cells of the retina from the choroid. This membrane is structurally similar to the blood-brain barrier, because the retina is an extension of the brain. A rupture of this barrier can cause diseases, like AMD, where the choroid blood vessels grow abnormally into the retina and cause damage, ultimately affecting vision.

carotenoids

Tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus.

Carotenoids can be synthesized fats and other basic organic metabolic building blocks by all these organisms.

cbt

see cell-based therapy

cell

The smallest building-block of a living being that is capable of functioning on its own.

A cell is 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). Conversion of many cells (of either the same or different functions) at the same spot in the body can form an organ with specialized purposes, like the retina, liver or brain.

cell-based therapy (cbt)

Using cell transplants or stem cells to treat a retinal degenerative disease.

Cell-Based Therapy (CBT) is one of the Foundation’s seven research priority areas. Scientists and clinicians are testing treatments for retinal degenerative diseases with stem cell and retinal transplants. This therapy has the 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 (cmm)

Determining how and why disease begins, and ultimately using this information to design an effective, targeted treatment.

Cellular and Molecular Mechanisms of Disease (CMM) is one of the Foundation’s seven 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. The resulting knowledge is being used to create effective, directed treatments.

central nervous system

The “central command system” of the body, it includes the brain, spine and retina.

The central nervous system (CNS) is the “central command system” of the body, and includes the brain, spine and retina. Every nerve outside of the blood-brain and blood-retina barriers is considered part of the peripheral nervous system. Since the retina is part of the CNS, it is possible that treatments for other neurodegenerative diseases of the CNS (like Lou Gehrig’s disease or Alzheimer’s disease) could work for retinal degenerative diseases.

choroideremia

Choroideremia is a rare inherited disorder that causes progressive loss of vision due to degeneration of the choroid and retina.

chromosome

A “package” of DNA that holds the genetic code to life. In humans, each non-sex cell has 23 pairs of chromosomes.

ciliary body

A ring of tissue that contains muscles and “fibers” that adjust lens thickness to focus light on the retina, so that we can see. In addition, it produces fluid to provide nutrients and take away waste from the lens and cornea, thus helping to control eye pressure.

The ciliary body, located in a “ring” around the iris, is responsible for controlling the shape of the lens, via muscle connections to “fibers” attached to the lens, a process that controls how light focuses on the retina. In addition, it creates fluid (called aqueous humor) that provides nutrients to and takes waste away from the lens and the cornea. Glaucoma drugs target the ciliary body to lower aqueous humor production and cause a drop in the intraocular pressure.

cilia (singular, cilium)

Cilia are very small, hair-like structures that are found in or on many specialized cell types (for example, photoreceptors and ear, kidney, and lung cells). A mutation in a gene whose protein helps maintain the structure of these “hairs” can cause diseases with symptoms in one or more affected body systems, creating a syndrome. For example, some Usher syndromes involve vision and hearing problems, caused by altered cilia proteins found in both photoreceptors and ear cochlear cells.

cmm

see cellular and molecular mechanisms of disease

cone cell

A type of photoreceptor, it detects light and is responsible for providing fine detail, daylight and color vision.

Cone cells are cone-shaped photoreceptors that detect light for vision. 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 discerning facial features 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.

cone dystrophy

see achromatopsia

cone-rod dystrophy

Cone-rod dystrophy results from a primary loss of cone photoreceptors, followed by loss of rods.

Cone-rod retinal dystrophy characteristically leads to early impairment of vision. An initial loss of color vision and of visual acuity (due to loss of cone function) is followed by nyctalopia (night blindness) and loss of peripheral visual fields (due to loss of rod function). In extreme cases, these progressive symptoms are accompanied by widespread, advancing retinal pigmentation and chorioretinal atrophy of the central and peripheral retina. For related but different diseases, see achromatopsia, cone dystrophy and rod-cone dystrophy.

congenital stationary night blindness (csnb)

An inherited eye disorder that is not progressive (“stationary”) and principally affects the rod photoreceptors in the retina, impairing night vision.

There may also be moderate to high myopia (short sightedness). The disorder is usually diagnosed by electroretinogram.

copper

A nutritional mineral that is required for proper functioning and maintenance of the body.

Copper is a mineral that is required for nutrition and proper functioning and maintenance of the body. Copper (2 mg) is one component of the AREDS clinical trial daily nutritional supplementation for treatment to slow vision loss in AMD. Copper was added to the AREDS formulation to protect the retina from potential unwanted damage from too much zinc oxide supplementation. If you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring or a non-typical approach and nutritional supplements may interfere with prescribed medicines.

cornea

The clear dome or “window” that covers the front of the eye, it provides a large part of the focusing ability of the eye.

The cornea is the clear dome that covers the front of the eye. It starts to focus light onto the lens. If the eye is like a camera, consider the cornea to be like a UV (ultraviolet) filter screwed onto the end of the camera lens. This is the part of the eye that undergoes vision-correcting LASIK surgery.

cortical implant

An implant into the part of the brain that interprets vision signals that come from the retina. Connecting this implant with a vision aide, like camera-glasses, may be a way to return vision to those who are blind.

A cortical implant is a chip or cable that is implanted into the visual cortex, the specific portion of the brain found at the back of the head that interprets visual information. This device would theoretically transmit to the cortex the visual images received from camera-like sunglasses (or another type of vision-detecting machine). The goal of this device is similar to a retinal prosthetic, but bypasses the retina and optic nerve completely, possibly restoring vision in patients who are completely blind.

csnb

see congenital stationary night blindness

dha (docosahexaenoic acid)

A healthy, highly unsaturated fatty acid (a type of omega-3 fatty acid) that is found in foods (e.g., tuna, salmon) and dietary supplements, implicated in photoreceptor function.

DHA is 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. Clinical trials are currently in progress to test whether DHA used as a nutritional supplement can slow the progression of X-linked RP, the dominant form of Stargardt disease, Usher syndrome and age-related macular degeneration. If you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring or a non-typical approach and nutritional supplements may interfere with prescribed medicines.

dna (deoxyribonucleic acid)

The chemical “blueprint” for life. Genes are made of DNA and gene mutations can cause diseases.

DNA is a long chain of building-blocks (called nucleotide bases) that carries the genetic instructions (genes) for making living organisms. Each DNA building-block can be thought of as a “letter.” When there’s a gene mutation (or “spelling mistake” for even one letter), it can potentially create a non-functioning protein that causes disease. Each gene makes a messenger called RNA, which then is the template for making proteins, the actual work-horses of the cell. DNA is found in the nucleus of a cell where it is packaged into highly specific, long chains called chromosomes (there are 23 chromosome pairs in humans).

docosahexaenoic acid

see dha

dominant

see autosomal dominant disease

drusen

Yellow-white retinal deposits thought to include proteins, pigments and fats. Dry AMD or juvenile macular degeneration may occur when drusen become too large or numerous and collect around the macula.

Drusen are yellow-white retinal deposits that may contain a mixture of proteins, pigments, fats and other wastes, and mainly concentrate around the macula. These 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. Scientists are still determining the exact composition and origin of drusen deposits, and how they can promote retinal disease.

FDA

Acronym for the Food and Drug Administration, a branch of the United States (US) Department of Health and Human Services.

FFB

Acronym for Foundation Fighting Blindness.

Foundation Fighting Blindness Clinical Research Institute

The Foundation Fighting Blindness Clinical Research Institute (CRI) has become the Retinal Degeneration Fund, a 501©(3) not-for-profit subsidiary of the Foundation Fighting Blindness. The RD Fund is a venture philanthropy vehicle created to help accelerate life-changing outcomes for people with retinal degenerations through direct mission related investments in therapeutic companies. RD Fund investments are funded by donations and serve the mission of the Foundation Fighting Blindness – to develop preventions, treatments and cures for retinal degenerative diseases, including Stargardt disease, retinitis pigmentosa, Usher syndrome, and macular degeneration. The RD Fund was launched with over $70M under management and is governed by an independent board of directors. With success, all proceeds are returned back to the RD Fund and the Foundation Fighting Blindness to provide resources to further its mission. For more information, please visit www.RetinalDegenerationFund.org

gene

A unit of inheritance, encoded by DNA. If there’s a mutation in a gene, this may cause a disease.

A gene is an organized sequence of building blocks for DNA (nucleotide bases or “letters”) that “spells out” the information necessary to create a specific messenger called RNA that, in turn, makes a specific protein. Every cell in the body has the same genetic “blueprint”; however, each organ uses a highly specialized combination of genes to produce proteins that are essential to the function and specialty of its particular cells. For example, in the eye, 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. Any disruption in the function of the above-mentioned (and other) proteins can cause a retinal degenerative disease.

gene mapping

Identifying a region of a chromosome that is responsible for causing a disease (or causing some known function), but not yet identifying the exact gene.

Gene mapping is the process of identifying a specific region (or locus) along one of the 23 paired chromosomes that contains a gene with a disease-causing mutation. This is also known scientifically as “positional cloning.” You can think of a region as a “neighborhood” and the gene that causes a disease as the “house” in that neighborhood. Once scientists have narrowed down the possibility to a particular locus/neighborhood on the chromosome, then they can identify the exact gene/house linked with that disease.

gene therapy (gt)

A therapeutic process that replaces or turns off the “bad” or mutated disease-causing gene and restores some level of normal protein function.

Gene therapy (GT) is one of the Foundation’s seven research priority areas and can be defined as the delivery of a gene or genetic information into cells for the purpose of achieving a therapeutic effect. At least three forms of gene therapy (gene replacement therapy, ribozyme therapy and RNA interference or 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 (ge)

Generally, it is defined as the study of inheritance; specifically, it is the determination of genes linked with causing retinal degenerative diseases.

Genetics (GE) is one of the Foundation’s seven research priority areas. Scientists and clinicians are looking for new genes linked to retinal degenerative diseases. It is thought that over half of retinal degenerative disease-causing genes have already been identified.

Genetic Testing (also called Genotyping)

Generally, is defined as determining the genetic make-up of an individual; specifically, is looking for the gene(s) that cause an individual’s retinal degenerative disease.

Genotyping is the process of screening patients’ DNA samples 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 on the FFB website. Scientists are attempting to connect the genotype (see Genetic Testing) with the phenotype (physical and clinical symptoms) for every disease.

geographic atrophy (ga)

Geographic atrophy may be considered the end stage of dry age-related macular degeneration (AMD), causing severe vision loss. Over time, sometimes over many years, the atrophy of the RPE cells (due to drusen deposits in the retina) gets more prevalent with all of the macula being affected.

Geographic atrophy looks like a circle or spot of degeneration, right in the center. Also see age-related macular degeneration.

gt

see gene therapy

gyrate atrophy (ga)

Gyrate atrophy is an autosomal recessively inherited disorder, which is due to a lack of the protein enzyme ornithine keto-acid aminotransferase (OAT), resulting in an increased blood serum level of ornithine (hyperornithinemia).

The symptoms are progressive “night blindness” and peripheral vision loss.

inner segment

The part of a photoreceptor cell that is closest to the front of the eye and is thought to channel light to the outer segment, where the visual cycle takes place.

The inner segment is one of the regions of a photoreceptor. In all vertebrates (animals with a spine), the inner segment serves not only as the site of energy production and oxidation, but also as a region of high refractive index (for light). The latter property causes the inner segment to act as a “waveguide” that channels light to the outer segment (where it is transformed into an electrical signal that travels down the optic nerve).

iris

The colored “ring” that regulates the amount of light that’s admitted into the eye.

An iris is 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 the iris to be like an aperture.

juvenile macular degeneration

see best disease; stargardt disease

lancelot

A Briard dog born blind with a mutation in the RPE65 gene that caused a dog-form of the human retinal degenerative disease called Leber congenital amaurosis (LCA). Lancelot has been treated with gene therapy and can now see.

As reported in the scientific journal, Nature Genetics, in 2001, researchers injected into 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. Three human clinical trials based upon this research began in 2007.

lca

see Leber Congenital Amaurosis

leber congenital amaurosis (lca)

Leber congenital amaurosis (LCA) is an inherited retinal degenerative disease characterized by severe loss of vision at birth. A variety of other eye-related abnormalities including roving eye movements, deep-set eyes, and sensitivity to bright light also occur with this disease. Some patients with LCA also experience central nervous system abnormalities.

lens

The transparent part of the eye that focuses light onto the retina, so that we can see.

The lens is an oval-shaped, clear (transparent) part of the eye behind the cornea and iris that focuses incoming light onto the retina. If the eye is like a camera, consider the eye lens to be like a camera lens.

locus (plural, loci)

A locus is the chromosomal “neighborhood” where a gene (a “house”) resides; specifically, a potential disease-causing gene.

A locus is a location in one part of a chromosome where a particular gene(s) might reside, like a “house” (gene) might reside in a “neighborhood” (locus). Scientists who are looking for genes associated with retinal degenerative diseases call it a locus until they definitively prove that one (or more) gene(s) in this region cause(s) that disease.

lucentis®

A blood vessel growth-blocking drug approved by the FDA in June 2006 for treatment of wet AMD.

Lucentis® is a drug approved by the FDA in June 2006 for treatment of wet AMD. In wet AMD, there is misdirected generation of vascular endothelial growth factor (VEGF) protein in the retina that causes choroid blood vessels to grow into the retina and become leaky, forming blood pockets in the retina. Lucentis®, an anti-VEGF drug, is actually a fragment of an antibody that binds to and blocks the parts of VEGF protein that promote vessel growth and leakiness, thereby reducing blood pockets. Approximately 95 percent of people treated with 0.5 milligrams of Lucentis® (in the MARINA clinical trial) lost only 1-2 lines (less than 15 letters) on a visual acuity chart one year after treatment. Up to 40 percent of treated individuals experienced three lines of improvement in visual acuity (15 letters) one year after treatment. On average, individuals treated with Lucentis® experienced an improvement of approximately 7 letters at two years compared to a loss of 15 letters in individuals who did not receive Lucentis®. Visit Genentech’s website for more information about this drug and the clinical trials.

lutein and zeaxanthin

Nutrient pigments chemically related to beta-carotene that are abundant in green leafy vegetables and yellow and orange-colored fruits and vegetables. These are the only two known food pigments that collect in the macula, where they are thought to protect it from light damage (blue light).

Lutein and zeaxanthin are nutrient pigments that are abundant in green leafy vegetables and yellow and orange-colored fruits and vegetables. These pigmented carotenoids (the general term for nutrient pigments, of which lutein zeaxanthin and beta-carotene belong) are highly concentrated around the macula and provide its characteristic yellow appearance. Lutein and zeaxanthin are thought to protect the macula from oxidative stress due to ultraviolet light exposure. A clinical trial-AREDS II, begun in October 2006-is testing a slightly adjusted AREDS supplementation in combination with different dosages of lutein, zeaxanthin and/or omega-3 fatty acids. If you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring or a non-typical approach and nutritional supplements may interfere with prescribed medicines.

macugen®

An anti-VEGF drug approved by the FDA in 2004 for treatment of wet AMD.

Macugen® is an anti-vascular endothelial growth factor (VEGF) drug approved by the FDA in 2004 for treatment of wet AMD. In wet AMD, there is over-expression of the VEGF protein in the retina that causes choroid blood vessels to grow into the retina and become leaky. This drug causes VEGF proteins to “stick” together, thereby inactivating them. This was the first approved anti-VEGF drug for treatment of a retinal degenerative disease and treated individuals showed an increase in 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%). Visit (OSI)eyetech’s website for more information about this drug and the clinical trials.

macula

The center of the retina that has a concentration of cone photoreceptor cells and is responsible for fine detail, day and color vision.

The macula is the central portion of the retina. The macula contains a dense concentration of cone photoreceptor cells that help us to see fine visual detail (see visual acuity), daylight and color vision. Only primates (including humans and monkeys) have a macula in their retina.

Messenger RNA (mRNA)

The processed gene “messenger” (derived from DNA) that is the template for making proteins. Also, see RNA.

Messenger RNA (mRNA) is the gene messenger that results from the transfer of genetic information from DNA into RNA. Often the orginal mRNA requires processing (i.e., cutting and “re-glueing”) into a shorter mRNA template for production of the final, proper protein.

metabolic process

A series of pathways the body uses, both to break down nutrients into simple energy packets and to create building blocks that then build-up cell components and help the body to function.

A metabolic process refers to methods used by the body to break down nutrients, using oxygen, and converting them into simple energy packets that the body can then use for maintaining cell functions necessary for life. Some waste products from this process include water and carbon dioxide. Oxidation (interaction between oxygen and all the different substances it may contact) is one part of the metabolic process; anti-oxidants help to control damage from too much oxidation. Please note: If you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring or a non-typical approach and nutritional supplements may interfere with prescribed medicines.

mutation

A change or “spelling mistake” in the DNA of a gene that can cause a disease (but sometimes does not cause disease).

A mutation is any change in the normal order of DNA “letters” (bases), a “spelling mistake” in the DNA, that define a specific gene. A disease-causing mutation is one which either disrupts the process of making mRNA (see mRNA) or alters the activity of the protein coded by that gene sufficient to make it non-functional. For example, many different mutations in the rhodopsin gene may cause retinitis pigmentosa (RP).

ne

see nutritional and environmental therapy

nei

Acronym for the National Eye Institute, a part of the research-funding government organization, the United States (US) National Institutes of Health.

neuroprotective therapy (np)

Delivering a protein or drug to the eye that prevents the photoreceptors and/or RPE cells from dying, thus saving vision.

Neuroprotective therapy (NP) is one of the Foundation’s seven research priority areas. Scientists and clinicians are testing delivery of survival proteins or drugs to protect the photoreceptors and/or RPE cells from dying (or preventing loss of light-detection capability). This is an especially important priority area that is sometimes called a “cross-cutting advance,” since neuroprotective survival proteins or drugs could potentially treat many different retinal degenerative diseases.

np

see neuroprotective therapy

nucleus

The specialized compartment within a cell that houses the DNA.

The nucleus is the specialized compartment within a cell that houses the DNA, packaged as chromosomes. The nucleus is also the location where RNA (messenger RNA) is made from genes and transported out of the nucleus to serve as a template for protein production.

nutritional and environmental therapy (ne)

A clinically-tested nutritional supplement or lifestyle change that has been proven to slow or stop the loss of vision in a retinal degenerative disease.

Nutritional and environmental therapy (NE) is one of the Foundation’s seven 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. Lifestyle changes, like the decision to stop smoking, can also lower risk for vision loss. If you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring or a non-typical approach and nutritional supplements may interfere with prescribed medicines.

nystagmus

Nystagmus is a constant, rapid and involuntary oscillation of the eyes - one of the symptoms that can be experienced by individuals who have a retinal degenerative disease, like Leber congenital amaurosis.

The constant, rapid and involuntary oscillation or movement of the eyes can be caused by a number of physiological problems, including issues with balance, eye muscles or fixation of vision. The eye movement can be side to side, up-down and/or circular. Individuals with Leber congenital amaurosis (LCA) may have nystagmus due to an inability to fixate their vision from an early age. It is interesting to note that dogs with LCA due to a mutation in the RPE65 gene had a reduction of nystagmus after having the RPE65 gene corrected with gene therapy treatment in only one eye.

omega-3 fatty acid

A type of fat that is important for cell function. Also, see DHA).

Omega-3 fatty acids are types of fat that are important for cell processes. The term “omega” refers to the specific configuration of chemical “double-bonds” and thus predicts the shape of the fat. There are many types of omega-3 fats that can be obtained from a number of food sources, including EPA (eicosapentaenoic acid; found in cold water fish and algae) and DHA (docosahexanoic acid; found in cold water fish and algae) and ALA (alpha-linolenic acid; found in some vegetable oils and nuts). AREDS II, sponsored by the Federal government’s National Eye Institute, is a clinical trial which started in October 2006 that is testing whether supplementation of omega-3 fatty acids and lutein and zeaxanthin can enhance the clinical effect of the already-proven AREDS supplementation (a specific combination of antioxidants and minerals). If you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring or a non-typical approach and nutritional supplements may interfere with prescribed medicines.

optic nerve

The bundle of nerve cells, or “cable,” that transmits signals from the retina to the visual processing center of the brain.

The optic nerve is the “cable” that receives the light detection signals from other retinal cells (photoreceptors initially detect the photons of light) and transports them to the part of the brain called the visual cortex where they are processed. A person doesn’t actually “see” until their visual cortex processes the signals. If the eye is a digital camera, consider this to be like the cable used to download the images from the camera onto a computer.

outer segment

The part of the photoreceptor cell that is directly adjacent to RPE cells, near the back of the retina, and is responsible for the conversion of light into electrical signals, via the visual cycle.

One of the parts of a photoreceptor cell. Specifically, it is the last part of the photoreceptor that light passes through on its first pass (i.e.,before any reflections) through the retina. Outer segments are composed of stacked disks (think of a stack of pancakes) that are flattened in planes perpendicular to the path of the light. The proteins involved with the visual cycle are found in the outer segments and convert light into electrical energy transmitted to the optic nerve.

oxidative stress/oxidation

Oxidation is the interaction between oxygen molecules and all the different substances they may contact. Oxidative Stress can occur when there’s an imbalance and a biological system can’t readily detoxify or easily repair the resulting damage, thereby promoting development of a retinal degenerative disease).

Oxidation is the interaction between oxygen molecules and all the different substances they may contact. Oxidative stress can occur when there’s a metabolic imbalance between the production of reactive oxygen species and a biological system’s ability to readily detoxify the reactive intermediates or easily repair the resulting damage to a cell. This damage may promote apoptosis, which may cause retinal degenerative disease. Certain anti-oxidants can protect a cell from this damage. Please note: if you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring or a non-typical approach and nutritional supplements may interfere with prescribed medicines.

peripheral nervous system

Nerves that are not part of the brain, spinal cord or retina, normally found in the extremities (e.g., arms, legs).

The peripheral nervous system (PNS) is not part of the brain, spinal cord or retina [although the cell bodies (control centers) for nerves that extend into the extremities (including arms and legs) are anchored in the brain and spinal cord]. The PNS is not protected by bone or the blood-brain barrier, leaving it exposed to toxins and mechanical injuries. Normally, peripheral nerves either control voluntary muscle movement (i.e., controllable processes like lifting an arm) or are involved in involuntary processes, like breathing, heart rate, etc. The retina is not considered to be part of the PNS.

phagocytosis

The process by which cells engulf materials (e.g., bacteria, dead cells) that are eventually killed, destroyed or digested. The outer segment tips of photoreceptor cells are phagocytosed every day by RPE cells.

Phagocytosis is the cell’s process of engulfing solid particles by the cell membrane, forming an internal “food vacuole” or “sack”. This sack is internalized and the contents are subsequently degraded and either released or retained for recycling. Some retinal degenerative diseases (e.g., some forms of Stargardt disease) are thought to be caused by problems with this phagocytosis.

phenotype

Physical symptoms of a retinal degenerative disease that can be clinically defined. Each phenotype is normally associated with a particular genotype (see genetic testing).

A phenotype consists of 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 therapy for the wet form of AMD that involves using a drug and a “cold” laser to destroy new, unwanted blood vessels.

Photodynamic therapy is for treating the wet form of AMD. This treatment involves injecting a light-activated drug (e.g., Visudyne® or Verteporforin®) into a 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 offers 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 after treatment.

photoreceptor cells

The light sensitive cells (rods and cones) in the retina.

Photoreceptor cells are 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 fine visual detail (see visual acuity, color, central and day vision. There are three types of cone cells, each of which detects colored light of a different wavelength (red, green and blue). In humans, rod cells are mainly found in the retinal periphery while cone cells are concentrated in the central portion of the retina (macula). Toxins, produced as byproducts of light detection by photoreceptor cells, are removed and/or recycled by the adjacent RPE cells.

phototransduction

The process of detecting light and converting it to an electrical signal that is then relayed to the brain via the optic nerve.

Phototransduction is also called the visual cycle. It is 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. Problems with proteins involved in phototransduction are responsible for causing certain retinal degenerative diseases.

proof of principle

The first measurable evidence that an experimental theory or therapy works.

A proof of principle is a scientific confirmation that a previously unproven idea or experimental therapy actually works (for instance, a drug produces a therapeutic effect in an animal model(s)). Proof of principle provides the first measurable evidence that an experimental therapy might also work in humans.

recessive

see autosomal recessive disease

retina

Thin layer of light-detecting cells at the back of the eye, similar to the film or digital sensor found in a camera.

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 considered to be an extension of the brain, and thus part of the central nervous system. The cell types and structures that are considered to be part of the retina include: photoreceptor nerve cells (rods and cones); other types of nerve cells that relay the signal to the optic nerve “cable” (horizontal, bipolar, amacrine, ganglion, Müller cells); retinal vessels; RPE cells; and, Bruch’s membrane. The photoreceptor cells of the retina absorb light and convert this light into electrical signals (see phototransduction). The electrical signals are transferred from the photoreceptors to other, secondary nerve cells (listed above) which then send the electrical signals through the optic nerve to the visual cortex region of the brain for interpretation.

retinal chip (also called artificial retina)

A light-detecting computer chip, designed to mimic basic photoreceptor cell light-detection function, that is implanted into the retina.

A retinal chip is a light-detecting 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. The chip works similar to a digital sensor found in the back of a digital camera. One example of this device: the company, Intelligent Medical Implants AG, is currently testing the “Intelligent Retinal Implant System (IRIS)TM” in a phase II clinical trial in Europe. Note: A retinal chip can be different from a retinal prosthetic.

retinal pigment epithelium (rpe)

A very thin cell layer found directly beneath the photoreceptor cells. RPE cells bring nutrients and oxygen to the photoreceptor cells, and supplies, recycles, and detoxifies products involved with the phototransduction process.

The retinal pigment epithelium (RPE) is a very thin, pigmented cell layer found directly beneath the photoreceptor cells. RPE cells sit 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 them to the photoreceptor cells, while also carrying away waste products from photoreceptor cells for disposal to the choroid. In addition, RPE cells recycle proteins and other components involved in the phototransduction process and provide other survival proteins to the retina. RPE cells phagocytose or “chew up” the ends of photoreceptor outer segments every day as a “preemptive strike” to prevent damage from built-up waste products.

retinal prosthetic

An implantable device that electrically stimulates the retina with information that it receives from a secondary light detection device (i.e., camera glasses).

This implantable device is not designed to detect light on its own (as found in a retinal chip), but stimulates the retina to send signals to the optic nerve in response to input from camera glasses (or another secondary vision detection device). One example of this device: the company, Second Sight, is currently testing the “ArgusTMII Retinal Stimulation System” in phase II clinical trials in the US. Note: A retinal prosthetic is not necessarily a retinal chip.

retinal transplantation

Injecting a layer of cells (already composed of photoreceptor and/or RPE cells) into the retina to replace dying cells.

Retinal transplantation is injecting a layer of cells (already composed of photoreceptor and/or RPE cells) into the retina, near the macula, with the purpose of replacing dead or dying retina cells. 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 (either with or without integration into the retina) by producing survival proteins that would keep remaining photoreceptor cells from dying and improve their detection of light and/or transmission of signals. Clinical trials are currently underway.

retinal vessels

The vessels found on top of the retina at the back of the eye that look like “tree branches” when viewed by an ophthalmologist during an eye exam.

Retinal vessels are the vessels found on top of the retina at the back of the eye that look like “tree branches” when viewed by an ophthalmologist during an eye exam. These vessels become damaged and leaky during eye diseases like diabetic retinopathy, retinopathy of prematurity and other diseases.

retinitis pigmentosa

Retinitis pigmentosa (RP) refers to a group of inherited diseases causing retinal degeneration. The most common feature of all forms of RP is a gradual breakdown of rods and cones.

Most forms of RP first cause the breakdown of rod cells. These forms of RP, sometimes called rod-cone dystrophy, usually begin with night blindness. RP is typically diagnosed in adolescents and young adults. It is a progressive disorder. The rate of progression and degree of visual loss varies from person to person. RP can be inherited in a dominant, recessive or X-linked fashion.

retinoschisis (also known as x-linked retinoschisis; xlrs)

Retinoschisis is vision loss due to the splitting of retinal layers and retinal deterioration due to a mutation in the retinoschisin (RS1) gene.

The RS1 protein is thought to act like a “glue” to hold together the retina. RS1 is an X-linked gene, where it is normally males who show symptoms of this disease. In addition to visible degeneration of the retina, the electroretinogram (ERG) is a negative (b-wave more reduced than a-wave).

rhodopsin

A light-detecting component (a visual pigment) of rod photoreceptor cells composed of a protein called opsin that is chemically linked to a processed fragment of vitamin A.

Rhodopsin is formed when a protein called opsin is chemically linked to a specialized/processed fragment 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 vitamin A fragment 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 that reduces the amount of “bad” gene product (“bad” RNA) to allow “good” protein to be made from good, non-mutated RNA.

Ribozyme therapy is a form of gene therapy normally used for autosomal dominant forms of retinal degeneration (to reduce the amount of “bad” gene product in a cell). In autosomal dominant disease, individuals 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. In this instance, ribozymes disrupt the mutant gene’s ability to produce the harmful protein by “chewing-up” the gene’s RNA messengers. For autosomal recessive disease, ribozyme therapy can be used in combination with gene therapy to install a “good” copy of the gene that produces RNA that is resistant to the ribozyme.

RNA

A family of gene products whose most common member, messenger RNA (mRNA), isused as a template for making protein.

“Messenger” RNA (mRNA) is derived directly from a gene and becomes the template for making a protein. Scientists and clinicians are currently testing approaches that target mRNA in many treatments for retinal degenerative diseases.

rnai therapy

A treatment method that destroys “bad” RNA to get rid of “bad” disease-causing protein.

RNA interference (RNAi) therapy involves creating a short piece of gene “sequence” or DNA “letters” that, when injected into the eye, can interact with native RNA and mark them for destruction. This method is useful for destroying “bad” RNA from mutated genes, to prevent production of toxic or harmful proteins (dominant disease). Scientists and clinicians are currently testing combinations of RNAi therapy with gene therapy to also replace the “bad” gene with a “good,” or functioning, gene (recessive disease).

rod cell

A photoreceptor cell responsible for black and white, night and peripheral (side) vision.

A rod cell is a rod-shaped photoreceptor cell that is located throughout the retina but is more common outside of the central macular region of the retina (i.e., is found in the periphery of the retina). The rod cell is particularly important for black and white, night and peripheral (side) vision. In many forms of RP, rod cell loss leads to what is sometimes referred to as “tunnel vision.”

rod-cone dystrophy/degeneration

Rod-cone dystrophy results from a primary loss of rod photoreceptors, followed by loss of cones.

The term, rod-cone dystrophy is used as an ‘umbrella term’ to imply retinal defects that impact primarily rod cells, with cone cells spared, at least until later stages of the disease. It can be used to generically define any retinal degenerative disease that exhibits this condition.

Retinitis Pigmentosa is considered a rod cone dystrophy, as is Leber Congenital Amaurosis and Usher syndrome. Note that rod-cone dystrophy is a different disease entity than Cone-Rod Dystrophy.

rp

see retinitis pigmentosa

rpe

see retinal pigment epithelium

sclera

The tough, outer, protective shell of the eye.

The sclera, also called the “white of the eye” is the tough outer protective shell of the eye. If the eye is like a camera, consider the sclera to be like the camera body.

sex chromosomes

The chromosomes inherited from both parents that contain the genetic material that determines the sex of an individual. X-linked diseases are caused by mutations of genes on the X chromosome.

The sex chromosomes are the X and Y chromosomes inherited from a biological mother and father. The inherited combination of X and Y chromosomes determine the sex of the baby. Normally, a female/woman inherits two X chromosomes (one from each parent) and a male/man inherits 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 X-linked retinal degenerative diseases.

stargardt disease

Stargardt disease is the most common form of inherited juvenile macular degeneration. The progressive vision loss associated with Stargardt disease is caused by the death of photoreceptor cells in the central portion of the retina called the macula.

Decreased central vision is a hallmark of Stargardt disease. Side vision is usually preserved. Stargardt disease typically develops during childhood and adolescence. Also involved in Stargardt disease is a region beneath the macula called the retinal pigment epithelium. Since mutations in certain genes may cause the build-up of a toxin called A2E (a break-down product of vitamin A), vitamin A supplementation nutritional therapy is not recommended for some individuals with Stargardt disease. if you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring or a non-typical approach and nutritional supplements may interfere with prescribed medicines. For information on another juvenile macular degeneration, see Best Disease.

stem cell

A self-renewing, unspecialized cell that is capabile of becoming any one of a number of more specialized cells.

A stem cell is a primitive, unspecialized cell that has the capacity to self-regenerate, but develops 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 in the human retina have been found in the ciliary body, a specialized structure that sits on either side of the iris, near the retina. These ciliary stem cells usually lie dormant in the adult. Stem cells have now been isolated by many scientific groups and are being evaluated as a potential source for replacement of RPE and photoreceptor cells. There are many different types of stem cells, including adult and embryonic stem cells. Adult stem cells are from mature tissue that can renew itself but has a limited ability to transform into specialized cell types (i.e., fewer cell options). Embryonic stem cells, being from early stages of development, have the theoretical potential to produce any kind of cell in the body.

strabismus

A misalignment of the eyes (pointing in and/or out). This situation may be due to eye muscle problems.

A misalignment of the eyes in which each eye, simultaneously can point in a different direction. Crossed eyes (esotropia) are one type of strabismus; “wall-eyes” (exotropia) are another. The exact cause is unknown, but it appears to be a problem with the eye muscles. Strabismus can affect depth perception.

survival factors/proteins

Also see neuroprotective therapy. Proteins, or drugs, that promote the health and survival of nerve cells, including photoreceptors.

Survival factors are drugs or biologically-occurring proteins 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). CNTF is a survival factor/protein that is being used in clinical trials for RP and dry AMD.

trans fats (also, see unsaturated fatty acid)

Unhealthy types of fat that may increase the risk of developing AMD.

Trans fats are unhealthy types of fat that may increase the risk of developing AMD. These are chemically-modified fats that increase the shelf life of the products to which they are added (to prevent the products from going “rancid”). The FDA now requires that companies list the amount of trans fats in their product on food labels. However, 0 grams of trans fats means that there are less than 0.5 grams per serving. If the label says that there are 0 grams trans fats, but the ingredients list that there are “hydrogenated” or “partially hydrogenated” fats or oils, then there are trans fats in the product (just less than 0.5 g per serving). Please consult with your personal physician and ophthalmologist before making any nutritional or lifestyle changes, as your personal health situation may require monitoring or a non-typical approach.

ultraviolet (uv) light

A radiant component of sunlight, invisible to the eye, that is characterized by short wavelengths and high energy. It will damage the retina (as well as the skin) with lengthy, unprotected exposure. If you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring or a non-typical approach and nutritional supplements may interfere with prescribed medicines.

Ultraviolet (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 (wavelengths of 400-315 nm), also called Long Wave or “blacklight”; UVB (wavelengths of 315-280 nm), also called Medium Wave; and UVC (wavelength less than 280 nm), also called Short Wave or “germicidal” (because it kills pathogenic organisms on exposed surfaces). To protect your eyes, it is recommended that you wear sunglasses that block all forms of UV light. This is particularly important for those who have retinal degenerative diseases, because their retinas may be more susceptible to damage or vision loss from exposure to UV light (depending on the nature of their disease).

unsaturated fatty acid

There are many different types of this dietary fat - some have been linked to positive health effects (see DHA; docosahexaenoic acid) and others have been linked to a risk of developing cardiovascular disease and AMD (see trans fats).

usher syndrome

Usher syndrome is an inherited condition characterized by hearing impairment and progressive vision loss. Balance may also be affected. Symptoms vary from person to person and progress at different rates.

There are at least three different forms of Usher syndrome. People with Usher syndrome type 1 (USH1) are born completely deaf and experience problems with balance. The first signs of RP - night blindness and loss of peripheral vision - usually appear in early adolescence.

In Usher syndrome type 2 (USH2), newborns have moderate to severe hearing impairment. Symptoms of RP typically start shortly after adolescence. Visual problems progress less rapidly than in Usher type 1 and hearing loss usually remains stable.

A rarer third type of Usher syndrome (USH3) was documented in 1995. Children with USH3 are usually born with good or only mild impairment of hearing. Their hearing and vision loss is progressive, starting around puberty. Balance may be affected.

Hearing loss in Usher syndrome is due to a genetic mutation (alteration) affecting nerve cells in the cochlea, a sound-transmitting structure of the inner ear. The same genetic defect also adversely affects photoreceptor cells in the retina, leading to vision loss. Recently, scientists have discovered that some Usher syndrome genes code for proteins that support cilia, fingerlike projections found on many cells, including photoreceptors and cochlea cells. This may explain why one individual may have both vision and hearing problems.

For another disease where damage to cilia may be causing visual impairment paired with problems in another system, see Bardet-Biedl-Syndrome.

vector

The “vehicle” or carrier for delivering genes or genetic information into the cell, particularly useful for gene therapy.

A vector is 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 (“good”) 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 two decades, researchers have been working to genetically modify viruses to be safe and have few immune side effects, without compromising their delivery capabilities. Examples of viral vectors include: lentiviral vectors, adeno-associated vectors (AAV), and encapsidated adenovirus minichromosome (EAM). The clinical trials for LCA (RPE65) gene therapy use retina-specific AAV vectors.

vegf (vascular endothelial growth factor)

A class of proteins that causes new blood vessel growth (angiogenesis) and maintains the natural “leakiness” inherent in vessels. These are normal body functions, which, if they happen where they shouldn’t (such as in the retina), can cause disease, such as AMD.

VEGF is comprised of a class of proteins that cause new blood vessel growth (angiogenesis), which are needed for normal body functions, like development, wound repair and the menstrual cycle. It is thought that abnormally high levels of VEGF (or its presence in places where it shouldn’t be expressed) cause disease. Several anti-VEGF targeted treatments are being used for treatment of wet AMD (as well as several other diseases that have unwanted blood vessel growth, like colon cancer), including the drugs Macugen® and Lucentis®.

verteporforin®

see photodynamic therapy

visual acuity

A measure of the ability to distinguish fine visual details.

Visual acuity is the clarity of vision held by an individual and is measured as a fraction of normal vision: 20/20 vision indicates an eye that sees at 20 feet what a normal, “standard” eye should see at 20 feet; 20/400 vision indicates an eye that sees at 20 feet what a normal eye sees at 400 feet. Usually measured with a letter chart (Snellen), it can also be measured using pictures, black and white lines or visual evoked potentials.

visual cycle

see phototransduction

visual field

The entire area that the eye can see from side to side without physically moving the eyes or head (includes peripheral vision).

The portion of the environment that the eye sees, on fixed forward gaze, includes the entire field of vision (central and peripheral) and is measured by a perimetry test. The normal field of vision is about 140 degrees for each eye (monocular vision) and about 180 degrees for both eyes (binocular vision).

visudyne®

see photodynamic therapy

vitamin a (vitamin a palmitate)

see also Beta-carotene, Rhodopsin: Vitamin A is found in certain animal and milk products, fruits and vegetables (and as a commercial supplement) that is used as part of a nutritional treatment of RP.

vitamin c (ascorbic acid)

An anti-oxidant found in certain fruits and vegetables (and as a commercial supplement) that is used as part of a nutritional treatment of AMD.

vitamin e

An anti-oxidant found in certain oils, nuts, and other foods (and as a commercial supplement) that is also used as part of a nutritional treatment of AMD.

vitreous

The clear, jelly-like substance found in the middle of the eye that helps to regulate eye pressure and shape.

The vitreous is 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

A measure of the character of light, where certain wavelength ranges define and distinguish different “types” of light. The photoreceptor cell detects and chemically converts light of certain wavelengths within the visible range (between 400-700 nanometers or nm) into electrical signals that travel, via the optic nerve, to the visual cortex in the brain.

x chromosome

The inherited package (or chromosome) of DNA that contains genes that help to determine the sex of an individual. Two X chromosomes are inherited by females and one X chromosome and one Y chromosome are inherited by males. Mutation of a gene found on the X chromosome can cause X-linked diseases.

Of the 23 pairs of chromosomes that humans carry in each cell of their body (except egg and sperm cells), genes on a single pair of chromosomes (called X and Y) determine gender. A female/woman can only give the X chromosome to her offspring (children), because females have two X chromosomes (XX), while males/men can give either an X or a Y chromosome to an offspring, because males have one X and one Y chromosome (XY). Importantly, the X chromosome also contains many genes that have nothing to do with determination of gender. Mutations in genes on the X chromosome result in diseases that are transmitted to male offspring (who have a single X-chromosome) only from their biological mother (maternal inheritance), or to female offspring from their mother or father (maternal or paternal inheritance). These are called X-linked diseases. In most cases, male offspring are affected by X-linked disease while females may either be unaffected carriers or may be affected with an X-linked disease.

x-linked disease

see x chromosome

x-linked retinoschisis (xlrs)

see retinoschisis

xlrs

see retinoschisis

y chromosome

The chromosome (DNA package) passed-down from biological father to son that contains genes that determine male gender.

The Y chromosome is the sex chromosome passed-down from biological father to son that contains genetic instructions that give men their gender (and other body characteristics). Males inherit one Y chromosome from their father and one X chromosome from their mother, and are therefore 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

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 daily nutritional supplementation for treatment to prevent progression of vision loss in AMD (findings from AREDS clinical trial). Zinc oxide is also being tested in a new nutritional supplement formulation for the AREDS II clinical trial. If you use nutritional supplementation, please consult with your personal physician and ophthalmologist as your personal health situation may require monitoring.