A condition where the brain and the eye do not work well together. Also called “lazy eye,” this condition results in poor vision in the affected eye.


A medical test that looks at blood vessels in the body. This test helps doctors see how well blood is flowing through the vessels. Using something called a contrast, this test is conducted in a similar way to an x-ray. The most common angiography used for the eye is called “fluroscein angiography,” which looks at the tiny blood vessels at the back of the eye.


Aniridia is a condition where the iris is partially or completely missing. This condition is usually present at birth (congenital). Aniridia may cause a number of symptoms, such as rapid eye movements, lazy eye, and enlarged eyeball.


The natural process of cell death that occurs in the body. Part of the natural life cycle, apoptosis is a regulated process that happens throughout the body all the time (billions per day).

Batten Disease

A group of inherited diseases of the nervous system that may result in vision loss. Often diagnosed in childhood, this group of rare diseases is progressive and results in shortened life expectancy. Vision loss is one of the common symptoms of Batten disease. There are 10 different forms of the disease, defined by what gene causes the disease.


CADTH stands for Canadian Agency for Drugs and Technologies in Health. This is an independent organization that provides government and other decision-makers with evidence to help them make decisions regarding the Canadian health care system.


Some organisms such as bacteria are made of a single cell. In humans, different cell types come together to form different structures and organs. A cell is microscopic (very tiny) and is made of a small mass surrounded by a membrane. It contains important products that allow it to promote life. A cell contains different molecules that are unique and perform fundamental roles in all living beings. Cells are the smallest independently functioning living matter.


Layer of cells that lie between the retina and the sclera at the back of the eye. The purpose of the choroid is to provide oxygen and nutrients to the retina.


Thread-like structure that packages DNA sequences known as genes. DNA, the chemical composition of organic life, is strung together into sequences called “genes.” These are in turn packaged into larger, thread-like structures called “chromosomes.” Human beings have 23 pairs of chromosomes; 22 of these are shared between men and women, but the 23rd pair, the sex chromosomes, are different: women have two X chromosomes and men have an X and a Y chromosome, which is why diseases resulting from genetic mutations on the sex chromosomes are typically more common in men (women have an extra copy that is not mutated). Chromosomes and all their genetic information can be found within each cell of a body, making up a vast, though very tiny, library of repeated information.


Clear layer at the front of the eye that acts as a barrier, protecting the eye from dirt and germs.


A molecule that makes up the physical structure and function of all living things. Sometimes referred to as “the code of life,” DNA (deoxyribonucleic acid) is an extremely important molecule that determines the physical structure and functionality of almost all organisms. Shaped like a ladder that has been twisted, the famous “double helix,” DNA contains four chemical bases arranged like rungs holding the ladder together: A, T, C, and G, with A always pairing with T on the other side of the ladder, and C always with G. The order of these bases, collected in larger segments called “genes,” defines the shape of an organism and how its parts function. Because of its structure, DNA can replicate itself, a process at the heart of cell division: the ladder is “unzipped” down the middle, allowing the detached sides to pair with the appropriate bases and form new sequences.


Drusen are fatty deposits that develop in the eye. Sometimes this symptom is related to a higher risk developing age-related macular degeneration. Drusen usually have no symptoms, and are diagnosed during routine eye exams.


The progressive weakening of tissue or organs in the body. The word dystrophy is used to describe cell death. In the eye, dystrophy means certain parts of the eye are getting weaker or dying.

electroretinograph (ERG)

A test that measures how well the retina is working. During this test, you will wear a sensor on your eye to measure the electrical activity at the back of your eye on your retina. This test is used to diagnose inherited retinal diseases, as well as measure of the progression of retinal disease. As photoreceptors die, electrical activity on the retina decreases.

Fundus photograph

The process of taking a picture of the back, or fundus, of the eye. This picture shows the retina, optic disc and macula. Eye doctors use this medical test to measure the progression of eye diseases


One of the basic building blocks of biological life, regulating an organism’s physical structure and how it functions. They usually do this is through the creation of specific proteins, important molecules that build and repair tissue. Often, when a gene is mutated, it no longer creates the protein it has instructions for, leading to any number of issues, including vision loss. A person’s entire set of genes—called their “genome”—is contained within each of their cells, and the information those genes encode gets passed to one’s offspring.

genetic disease

A disease that is controlled by the genetic makeup of a living being.


A living being’s complete set of DNA. Each genome has all of the information needed to build and maintain the living being.

intraocular pressure

Similar to blood pressure, your intraocular pressure is an important diagnostic tool to determine your eye health. High intraocular pressure puts you at risk for glaucoma. This is measured using tonometry.


The iris is the coloured part of our eye that surrounds our pupil (the black center of our eye). The iris is a muscle that controls the size of the pupil. It helps the pupil change size depending on how much light is coming into the eye.


An eye condition that results in the progressive deterioration of the cornea. Symptoms include blurred vision that is not corrected with glasses. Depending on the stage and progression of the disease, treatments range from eye drops to surgery. The cause of keratoconus is not fully known, but has been linked to certain genes and environmental factors.


Small, central portion of the retina at the back of the eye, responsible for central vision.


Microbes are microscopic forms of life. They are found in water, soil, the air and in living bodies. The most common type of microbes are bacteria, viruses and fungi. While most microbes aren’t dangerous to humans, some are responsible for diseases.

National institute of health

National Institutes of Health (NIH) is similar to Health Canada. In the United States, the NIH manages the health and well-being of Americans, and people around the world. They include 20 separate organizations that work under the larger agency. Once of these organizations is the National Eye Institute


Ophthalmology is a division of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a Doctor of Medicine who focuses on the diagnosis and treatment of infections in the eye. All assessments that are designed to analyze eye disease should be performed by a physician. The practice of ophthalmology includes all features of visual function in health and disease.

Optical coherence tomography

Optical coherence tomography is a non-invasive imaging test. It uses certain light waves to create very detailed pictures of the layers of the retina, including the macula. These pictures help opthalmologists learn more about the health of a patient’s eyes, including whether there is fluid behind the retina, or thinning of the macula.


Way of using light to control genetically engineered cells. Researchers use optogenetics to very finely control nerves to better understand their function.


A tool used to measure the thickness of the cornea. There are a few methods for conducting this test. Doctors will use this test in the diagnosis of glaucoma, before certain eye surgeries, or in the diagnosis of keratoconus.


A type of cell that converts light into signals that the brain uses to create a picture. Housed in the retina at the back of the eye, photoreceptors are specialized cells that convert incoming light into electrical signals that can be interpreted by the brain. They come in two varieties: rod photoreceptors are responsible for peripheral and low-light vision, while cone photoreceptors are responsible for color and high-acuity vision. Many inherited retinal diseases entail the degeneration of rods and cones, leading to vision loss of various kinds.


The retina is a thin layer of light-sensitive tissue lining the back of the eye. Its role in vision is crucial: specialized retinal cells called “photoreceptors” convert incoming light particles into visual signals that, once sent along the optic nerve, are interpreted by the brain as vision. Every component of the human eye is designed to optimally receive and transfer light so that the retina can do its work.

Retinal Pigment epithelial (RPE) cells

Layer of cells at the back of the eye attached to the choroid. RPE cells provide nourishment to retinal cells, help absorb some light that comes into the eye, and provides other functions that support the retina.


A molecule that supports DNA in making all living things. Ribonucleic Acid, or RNA, is one of the three building blocks essential to creating life (the other two are DNA and proteins). Known as DNA-photocopy, RNA is created when a cell needs to produce a protein. RNA translates genetic code from DNA into usable proteins. RNA defects can result in a number of diseases, including heart disease, some cancers, and stroke.


The protective layer of the eye. Also known as the “white” of the eye, due to its white color.

stem cells

Stem cells are unspecialized cell that can be turned into a variety of cell types. Found in both adult tissue and embryos, stem cells have enormous medical potential because of their ability to be transformed into and replace cells that have been damaged or lost, including the retinal cells that are compromised in many retinal diseases.


A condition where the eyes are not properly aligned, which results in difficulty seeing. The eyes have trouble focusing on an object. This difficulty may be occasional or consistent. Some cases of strabismus may be treatment with physical therapy or surgery.


A tool used to measure intraocular pressure. After numbing drops have been applied, the doctor puts this pencil-shaped tool on your eye to determine the pressure in your eye.

vascular endothelial growth factor (vegf)

Vascular endothelial growth factor is a protein in the body that promotes the production of blood vessels. During conditions where a part of the body is not getting enough blood, VEGF is stimulated to form new blood vessels to bring more blood. In the eye, the release of VEGF can cause too much blood to enter the eye. This contributes to a number of diseases that may affect vision.

Visual acuity

A measurement of how well you see in front of you. Visual acuity of 20/20 is considered “perfect” vision. 20/20 visual acuity means you can see something 20 feet in front of you what can normally be seen at 20 feet. If you have 20/50 visual acuity, it means you need to be 20 feet away from an object that someone with perfect vision can see 50 feet away.

visual field test

A measurement of how well your central and peripheral vision are functioning. This test is used to measure how much peripheral vision you have. In the case of retinitis pigmentosa, your peripheral vision deteriorates over time. One type of field test is called automated perimetry. This test can show you how much vision you have left.

During a visual field test you will me asked to look at a central object, and detect objects (moving or still) on the edge of your vision. You may be asked to complete this test one eye at a time.


Zebrafish are a type of small fish that are often used in research. They belong to the minnow family. These fish provide useful models to study eye diseases because they are less expensive, smaller, and easy to grow. Their eyes also have a similar structure and function as human eyes.

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