Document Index

Glossary: Vision – Related Terms

Adaptive and Assistive Devices – Prescription and nonprescription devices that help people with low vision enhance their remaining vision. Some examples include magnifiers and telescopes, talking devices, and computer software.

Age-Related Macular Degeneration (AMD) – an eye disease that results in a loss of central, “straight-ahead” vision. AMD is the leading cause of vision loss. It makes reading, seeing faces, and performing other daily living tasks difficult.

Amsler Grid – a simple screening tool used for monitoring early signs of wet AMD (age-related macular degeneration).

Angiogenesis – growth of new blood vessels. When this process takes place in places where it should not, it can cause disease, for example in the wet form of age-related macular degeneration (AMD).

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 or fruit.

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

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 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.

Bionic Eye – A light-detecting computer chip designed to mimic basic photoreceptor cell light detecting function that is implanted into the retina. (Also called Retinal Chip)

Cataract – clouding of the lens. It can be present from birth (congenital) or can develop later in life. They are usually progressive, so require regular monitoring. People with a cataract see through a haze. In a usually safe and successful surgery, the cloudy lens can be replaced with a plastic lens.

Cell – the smallest building block of a living being that is capable of functioning on its own.

Cell Based Therapy – using cell transplants or stem cells to treat disease.

Choroid – a sheet of blood vessels behind the retina that brings oxygen and nutrients and removes waste.

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

Colour Blindness – the inability to identify colours in a normal way. Colour blindness is a colour vision deficiency that makes it difficult to impossible to perceive differences between some colours. Although colour blindness is usually an inherited condition, it may also occur because of eye, nerve, or brain damage, or due to exposure to certain chemicals. Colour blindness is typically identified as either total or partial, with total colour blindness being quite rare (see Achromatopsia on page 55).

Cone Cell – a type of photoreceptor that detects light and is responsible for providing fine detail, daylight and colour vision.

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.

Corneal Opacity – the cornea, which is normally clear, has become opaque for one of a number of reasons such as dystrophy (degeneration) or scarring or cloudiness caused by dehydration or over-hydration.

Degenerative – a gradual loss of function, as in degenerative retinal diseases – a gradual loss of sight as the retina stops working.

Diabetes – chronic disease related to high blood sugar that may lead to vision loss (diabetic retinopathy).

DNA (deoxyribonucleic acid) – the chemical “blueprint” for life. Genes are made of DNA and gene mutations can cause diseases.

Drusen – yellow-white retinal deposits thought to include proteins, pigments and fats.

Electroretinogram (ERG) – a test carried out by your eye care professional. It measures the electrical response of the light sensitive cells in the eye, the rods and cones, and it also measures retinal function.

Eye Care Professional – an optometrist or ophthalmologist.

Flashes and Floaters – a very common occurrence for many people. Floaters are little specks or threads that sometimes drift across the line of vision and flashes are little sparks of light that sometimes flicker across the visual field. Both are usually harmless but in some cases they can be a warning sign of trouble in the eye. If your flashes and floaters become more plentiful, you should consult your doctor for an eye exam.

Fluorescein Angiogram – a test carried out by your eye doctor. A dye, called fluorescein, is injected into the bloodstream and highlights the blood vessels in the back of the eye so they can be photographed.

Fovea – a small pit at the centre of the macula with a high concentration of cone cells.

Free Radical – a highly reactive chemical or nutritional breakdown product that can cause damage to a cell or tissue.

Fundus – the interior surface of the eye that includes the retina, fovea and macula.

Fundus Photographs – these are carried out by your eye doctor to look for any changes or abnormalities in the back of the eye.

Gene – a unit of inheritance, encoded by DNA. These stores of information tell our cells what to do and pass down family traits including hair and eye colour, as well as certain diseases. If there is a mutation in a gene, this may cause a 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 Therapy – a therapeutic process that replaces or turns off the faulty or mutated disease causing gene and restores some level of normal protein function.

Genetic Testing (also known as Genotyping) – determining the genetic make-up of an individual. In a clinical setting, it is looking for the gene(s) that cause an individual’s disease.

Genetics – the study of inheritance. Specifically, it is the determination of genes linked with causing disease.

Geographic Atrophy – an end stage of 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.

Glaucoma – the name for a group of eye conditions which cause damage to the optic nerve, typically caused by a clinically characterised pressure build-up in regards to the fluid of the eye (intraocular pressure-associated optic neuropathy). Early detection and treatment can limit vision loss due to glaucoma.

Hyperopia – long sightedness. When a person is long sighted, this means that they can see objects that are further away more easily than those that are nearer to them. Most people will have glasses that they need to wear for reading, watching TV, table top activities etc. This is because the eyes struggle to focus at all distances and this, if uncorrected, can lead to eyestrain.

Intra Ocular Injections – injections directly into the eye.

Intra Ocular Pressure – pressure within the eye.

Iris – the coloured “ring” that regulates the amount of light that is admitted into the eye.

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

Low Vision Therapist – a vision rehabilitation professional who trains people with low vision to use optical and non-optical devices and adaptive techniques to make the most of their remaining vision.

Low Vision – a visual impairment, not corrected by standard eyeglasses, contact lenses, medication, or surgery, which interferes with the ability to perform everyday activities.

Lutein and Zeaxanthin – nutrient pigments chemically related to beta-carotene that are abundant in green leafy vegetables and yellow and orange- coloured fruit 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).

Macula – centre of the retina that has a concentration of cone photoreceptor cells and is responsible for fine detail, day and colour vision.

Macular Hole – a problem that affects the very central portion of the retina. It happens for a variety of reasons such as eye injuries, certain diseases, and inflammation inside the eye. The most common cause is related to the normal aging process. Macular holes often begin gradually and affect central vision depending on the severity and extent of the problem. Partial holes only affect part of the macular layers, causing wavy, distorted, blurred vision. Patients with full-thickness macular holes experience a complete loss of central vision. Some macular holes seal spontaneously and require no treatment. In many cases, surgery is necessary to close the hole and restore useful vision.

Mutation – a change or “spelling mistake” in the DNA of a gene that can cause a disease (but not always).

Myopia – short sightedness. This means that the eye has difficulty when focussing on more distant objects; so glasses should be worn when prescribed.

Neuroprotective Therapy – delivering a protein or drug to the eye that prevents the photoreceptors and/or RPE cells from dying.

Nucleus – specialised compartment within a cell that houses DNA.

Occupational Therapist – a rehabilitation professional who works with persons with disabilities, including low vision, to complete the everyday activities that they need for independence and quality of life.

Ophthalmologist – a medical doctor specialising in the eye that can carry out specialised treatments or surgery. They diagnose and treat all diseases and disorders of the eye and prescribe glasses and contact lenses.

Optic Nerve – the bundle of nerve cells, or “cable” that transmits signals from the retina to the visual processing centre of the brain.

Optician – someone who makes or sells lenses (glasses or contacts) in accordance to an optometrist’s prescription.

Optometrist – a licensed professional who prescribes glasses and contact lenses, and diagnoses and treats certain conditions and diseases of the eye.

Orientation and Mobility Specialist – a vision rehabilitation professional who trains people with low vision to move about safely in the home and to travel by themselves.

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

Pathological (Degenerative) Myopia – a rare type of short-sightedness where the eyeball continues to grow becoming longer than it should be. Pathological myopia is quite different from the simple refractive myopia or near-sightedness that affects so many people.

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).

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.

Photoreceptor Cells – light-sensitive cells (rods and cones) in the retina.

Presbyopia – a refractive condition in which the accommodative ability of the eye is insufficient for near vision work due to ageing.

Proof of Principle – the first measurable evidence that an experimental theory or therapy works.

Retina – the thin layer of light-detecting cells at the back of the eye.

Retinal Chip – a light-detecting computer chip designed to mimic basic photoreceptor cell light detecting function that is implanted into the retina. (Also called Bionic Eye).

Retinal Pigment Epithelium (RPE) – very thin 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.

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).

Rhodopsin – 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.

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

Rod Cell – photoreceptor cell responsible for black and white, night and peripheral (side) vision.

Sclera – the white, tough, outer, protective shell of the eye.

Specialist in Low Vision – an ophthalmologist or optometrist who specializes in the evaluation of low vision. This professional prescribes magnifying devices.

Stem Cell – a self-renewing, unspecialised cell that is capable of becoming any one of a number of more specialised cells.

Sub Retinal Injection – injections that are given directly into the sub retinal space.

Vector – the “vehicle” or carrier for delivering genes or genetic information into the cells, particularly useful for gene therapy.

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

Vision Rehabilitation Therapists (VRTs) – Professionals who teach adaptive independent living skills, enabling adults who are blind or have low vision to confidently perform a range of daily activities.

Visual Acuity – a measure of the ability to distinguish fine visual details.

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

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

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

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, while one X chromosome and one Y chromosome are inherited by males. Mutation of a gene found on the X chromosomes can cause X-linked diseases.

Y Chromosome – the chromosome (DNA package) passed down from biological father to son that contains genes that determine male gender.

Zeaxanthin and Lutein – nutrient pigments chemically related to beta-carotene that are abundant in green leafy vegetables and yellow and orange- coloured fruit 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).


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