Inherited retinal diseases, sometimes called hereditary retinal dystrophies or congenital retinal degenerations, are a group of rare genetic disorders that can cause severe vision loss or blindness. IRDs are caused by mutations in one of more than 250 genes. IRDs affect around 2 million people worldwide.
What are IRDs?
Inherited retinal diseases (IRDs) are a diverse group of rare eye diseases, characterized by the progressive loss of function or death of photoreceptor (light-sensitive) cells in the retina, resulting in associated vision loss or blindness.
The underlying cause of all IRDs is the presence of mutations in genes involved in the development and normal function of photoreceptors or other retinal cells.
What causes IRDs?
Inherited retinal diseases are caused by mistakes, or mutations, in a specific gene that you inherit at birth. Depending on the gene involved one or both copies of the gene have to be mutated to cause IRDs. If one mutated gene is sufficient the inheritance mode is called dominant, if both are needed, the disease is recessive. In X-linked disease, the inheritance is different between men and women. In all cases the mutation causes the dysfunction of a specific protein so the retina cannot function properly. IRDs can be caused by hundreds of different mutations and only a genetic test can determine exactly what type you have.
Genetic testing is the only way to receive an accurate diagnosis and will help find out if there are treatments or clinical trials available.Genetic testing
Symptoms related to IRDs typically stem from the specific genetic mutation underlying the condition. Some people living with IRDs experience a gradual loss of vision, eventually leading to complete blindness, while others may be born with or experience vision loss in infancy or early childhood.
Going blind / progressive vision loss
Many IRDs are characterized by gradual vision loss during a patient’s lifespan that may eventually lead to blindness. In some IRDs severe visual impairment may be present as early as the first year of life. Some IRDs predominantly impact cone photoreceptors that are located in the central retina, leading to central vision loss. Other IRDs impact rod photoreceptors that are mostly located in the peripheral retina, leading to side, or peripheral, vision loss.
Tunnel vision is the loss of peripheral vision. As tunnel vision occurs, the only usable vision a person might have is central vision, which creates a tunnel effect as if someone is looking through a narrow tube. There are many different causes of tunnel vision and vision fields may eventually become so narrow that patients are blind. A few common causes of tunnel vision are optic nerve damage from glaucoma, eye ‘strokes’ or specific injury to the brain. Various inherited retinal diseases, including retinitis pigmentosa, lead to tunnel vision because genetic mutations cause degeneration of rod photoreceptors in the peripheral retina.
Night blindness “Nyctalopia”
Night blindness, or nyctalopia, is the inability to see well at night or in low light conditions. In the retina rod photoreceptors allow for seeing in dim light. Night blindness can occur if rods are affected by a certain condition or disease. Retinitis pigmentosa is an IRD that frequently causes night blindness in the early stages of disease. Treating night blindness depends on the cause and visiting an eye doctor will help with a proper diagnosis.
Sensitivity to light “Photophobia”
Photophobia is a common yet debilitating symptom that causes light sensitivity or an intolerance of light. A patient who has photophobia may experience eye discomfort in the sun or harsh indoor light. Photophobia is a symptom of many conditions, including infection or inflammation, that can irritate the eye. Light sensitivity might also be a symptom of an underlying disease not directly affecting the eye, such as migraine or meningitis. Other common causes of photophobia include detached retina, corneal abrasions and inherited retinal diseases including Leber congenital amaurosis.
Eye shaking “Nystagmus”
Nystagmus occurs when the eye makes involuntary repetitive back-and-forth eye movement and is sometimes called ‘wiggly eyes’ or ‘dancing eyes’. These movements can be up and down, rotational or side to side, and usually affect both eyes. Nystagmus often results in reduced vision and depth perception along with balance and coordination issues. This symptom occurs when the part of the brain or inner ear that regulates eye movement and positioning does not function correctly and can be either genetically based or acquired through injury or other circumstances.
Color blindness is a deficiency in the way a person sees color. People with colorblindness have a difficult time distinguishing certain colors and typically occurs when one or more types of color cone photoreceptor in the eye are absent or not working properly. Changes in color vision can sometimes signify a more serious problem and any variation to color perception should be reported to an eye specialist. Color blindness is also observed in people with inherited retinal diseases.
Is there a cure for IRD?
For people with RPE65 mediated retinal disease, a gene therapy is available. But, for the vast majority of IRD patients, there is currently no treatment available. At ProQR we are working hard to change that. We are developing several investigational RNA therapies for different forms of inherited retinal diseases including Leber congenital amaurosis, retinitis pigmentosa and Usher syndrome.
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