Glossary of Terms


Also known as ‘lazy eye’. Decreased vision in one or both eyes without detectable anatomic damage to the retina or visual pathways. Usually not correctable by eyeglasses or contact lenses.

Amsler Grid

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


This is the 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).


This is 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.


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


Astigmatism is when the cornea (the clear cover over the iris and pupil) is more half rugby ball shaped than the spherical, half football shape it is meant to be. The effect on the vision is to stretch out the image viewed in the area that the bulge occurs.

Sometimes the brain can compensate for astigmatism although it may be too strong for this to happen without the aid of glasses.

Autosomal Dominant Disease

Disease caused when an individual inherits a disease-causing mutation in one copy of a gene pair. Click here for more information about inheritance patterns.

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. Click here for more information about inheritance patterns.


Any chromosome within the 22 pairs of non-sex (not X or Y) chromosomes inherited by every individual from their biological parents. Click here for more information about human genetics.

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)


Clouding of the lens is known as cataract. It can be present from birth (congenital) or can develop later in life. They are usually progressive, so require regular monitoring.


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 a retinal degenerative disease.

Central Nervous System

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


A sheet of blood vessels behind the retina that brings oxygen and nutrients and removes waste. Click here for more information about the parts of the eye and how the eye works.


A “package” of DNA that holds the genetic code to life. In humans, each non-sex cell has 23 pairs of chromosomes. Click here for more information about human genetics.

Chronic Illness

An illness or disease that lasts a long time.

Colour Blindness

Colour blindness is 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. Click here for more information about the parts of the eye and how the eye works.


The clear dome or “window” that covers the front of the eye. It provides a large part of the focusing ability of the eye. Click here for more information about the parts of the eye and how the eye works.

Corneal Opacity

Corneal opacities mean that 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.


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

DNA (deoxyribonucleic acid)

The chemical “blueprint” for life. Genes are made of DNA and gene mutations can cause diseases. Click here for more information about human genetics.

Dry Eye

Dry eye, known medically as keratoconjunctivitis sicca or keratitis sicca, is a condition where there is a problem with the production of tears. Usually eyes feel irritated, dry and uncomfortable. Eyes may be red and there may be a burning sensation, or it may feel as if there is something in the eye. Sometimes there may be periods of blurred vision but these normally go away after a short while or on blinking. There are three main ways to help with dry eye; preserving the existing tear flow by reducing the temperature in rooms or blinking more, using artificial tears such as drops, gels or ointments, and reducing the draining away of the tears by a process called punctual occlusion which blocks the drainage holes in the lower eyelids.


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.

Electroretinogram (ERG)

This is a test carried out by your eye doctor. It measures the electrical response of the light sensitive cells in the eye, the rods and cones, and it also measures retinal function.

Flashes and Floaters

Flashes and floaters are 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

This is 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.


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.


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.




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)

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


The study of inheritance. Specifically, it is the determination of genes linked with causing retinal degenerative disease.

Geographic Atrophy

This 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.


Glaucoma is 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.


Also known as hypermetropia, hyperopia is 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

This refers to injections directly into the eye.

Intra Ocular Pressure

Increased pressure within the eye. E.g. Glaucoma.


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


This is a degenerative condition where the cornea thins and is pushed outwards, usually in the centre, by the internal pressure of the eye. Usually this is hereditary, occurs in both eyes and appears in the teens. It is associated with conditions such as Downs Syndrome. If untreated, it can result in a rupture, but sometimes it may stop in an earlier stage of its development or simply not progress that far. It is a condition which requires regular monitoring. In mild cases, spectacles will offer correction of the refractive problems. Contact lenses may be required for more advanced cases.


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

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).


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

Macular Hole

Macular hole is 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. However, 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.


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


Myopia is 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.


The specialised compartment within a cell that houses DNA.


Nystagmus is a constant, rapid and involuntary oscillation of the eyes – one of the symptoms that can be experienced by patients who have a retinal degenerative disease, like Leber congenital amaurosis. This is a condition where the eye moves almost constantly. It can either be vision related or due to muscular imbalance. If vision related, it often indicates deterioration in the central field of vision, such as macular degeneration or loss of central vision. It occurs as the eye is relying largely on rod cells in the peripheral retina which require movement to focus on an object or else it will fade out. If the object is not moving then the eye will move as it attempts to keep the object in focus.


A medical doctor specialising in the eye that can carry out specialised treatments or surgery.



Optic Nerve

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


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


A licensed professional who examines your eyes for defects in vision or eye conditions in order to prescribe corrective lenses or appropriate treatment.

Oxidative Stress / Oxidation

Oxidation is 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 a retinal degenerative disease.


Usually results from a head injury. Optic disc appears raised above the level of the retina.

Pathological (Degenerative) Myopia

Pathological myopia is 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 with the growth of leaky blood vessels that grow in the back of the eye, a condition your doctor may call choroidal neovascularisation. The development of choroidal neovascularisation is associated with serious impairment of vision and, in some cases, profound vision loss.


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

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


This is 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.


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

A 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).

Retinal Tear / Detachment

Retinal detachment is a condition where the retina separates from the underlying choroid layer of the eye. Retinal detachments have many causes, including aging, surgery, trauma, inflammation, high myopia and diseases such as diabetic retinopathy, retinopathy of prematurity and scleritis. Symptoms include light flashes, floaters, shadow coming down over vision, blurred vision and vision loss. A retinal tear often occurs before a detachment. When the fluid migrates beneath the retinal tear, it can lift the retina off of the back of the eye leading to detachment. Surgical outcomes have now vastly improved in recent years and anatomic re-attachment of the retina most often leads to recovery of at least some visual function. Visual outcomes are best when the detachment is discovered and treated without delay.


Retinopathy of Prematurity

Retinopathy of Prematurity (ROP), also known as retrolental fibroplasia, is a potentially blinding condition affecting the retina of new-borns. ROP mainly affects the retinal blood vessels. When the development of the retinal blood vessels is incomplete, the retina is not receiving enough oxygen so tries to grow new vessels. These new vessels are fragile and cause scarring. The factors that put infants at greatest risk of developing ROP are low birth weight (less than 3.5 pounds) and premature delivery (26-28 weeks). The overwhelming majority of these babies will have mild ROP and will not require treatment. Although the incidence of ROP is on the rise due to increased survival of very premature babies, medical advances mean fewer babies require treatment. If treatment is required, laser therapy is used to stop the growth of these blood vessels. Other therapies including Anti-VEGF injections are currently being explored for their effectiveness in ROP.


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.


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

Rod Cell

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


The white, tough, outer, protective shell of the eye.

Stem Cell

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


A strabismus is basically a squint. The main effects of a strabismus are that usually the person will have one eye that is stronger than the other. This is because the brain has to give priority to one eye over the other with the result that the weaker one does not ‘learn’ to see as well as the stronger one. In practical terms, a person should be guided from their weaker side to allow them to make full use of their stronger eye, but in contrast, should be approached from or have objects presented to their stronger side.

Sub Retinal Injection

This refers to injections that are given directly into the sub retinal space.


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


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.

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).


The 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).