Choroideremia vs Retinitis Pigmentosa

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Choroideremia vs Retinitis Pigmentosa - Symptoms & Differences a

Choroideremia vs Retinitis Pigmentosa – Symptoms & Differences:

Choroideremia

It is a rare, congenital eye disorder that is inherited in an X-linked recessive manner.

Statistics

According to the data, 1 in 50,000 to 100,000 people has this eye disorder, and it occurs almost exclusively in males.

Choroideremia accounts for about 45 of all blindness. Most people who suffer from this eye disorder lose their vision completely by the time they are middle-aged.

Choroideremia is occasionally misdiagnosed since it can be confused with retinitis pigmentosa, which is also genetic and presents with similar symptoms.

Symptoms

The signs and symptoms include:

  • atrophy of retinal layers;
  • night blindness;
  • blindness;
  • loss of peripheral vision;
  • progressive vision loss;
  • obesity;
  • deafness;
  • mental retardation;
  • reduced central vision.

Causes

The cause of atrophy of retinal layers is a mutation in the CHM gene which encodes for a certain protein (Rab escort protein-1), that is required for normal and healthy eye function. Without the help of Rab proteins in intracellular trafficking, cells die prematurely.

Diagnosis

Your healthcare professional will perform tests that examine your visual field. In addition, he will look inside the eye for the degeneration of the retina. Furthermore, there is a genetic blood test to diagnose the disorder that was created by Dr. Ian MacDonald.

Treatment

There is currently no cure or effective treatment for Choroideremia.

Retinitis Pigmentosa

Retinitis pigmentosa comprises a large group of inherited vision disorders that cause progressive degeneration of the retina – the light-sensitive tissue at the back of the eye which contains photoreceptors. There are two types of photoreceptors:

  • cones – they are not sensitive to lower light levels and require bright light to function. They are responsible for high spatial acuity and are capable of color vision.
  • rods – they provide peripheral vision and are most sensitive to movement/motion. Rods are also responsible for dark adaptation. They have a low spatial acuity and do not mediate color vision.

In retinitis pigmentosa, the rod cells and the cone cells stop working, leading to vision loss.

Note – one part of the retina does not contain photoreceptors. This is called the blind spot.

Statistics

According to statistics, retinitis pigmentosa affects roughly 1 in 4,000 individuals. Also, around 100,000 Americans have the disorder, mainly caused by gene mutations inherited from one or both parents.

It commonly starts later in life and progresses to blindness. By age 40, most sufferers have a central visual field of less than 20 degrees in diameter and are legally blind.

The term retinitis pigmentosa was first coined by a Dutch pioneer of vision and psychological sciences called Frans Cornelis Donders, in the middle of the 19th century.

Symptoms

Common symptoms include:

  • need for more light;
  • decreased response to magnification;
  • night blindness;
  • donut shaped visual field loss progressing to severe constriction.

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Causes

Parents can pass the affected genes on to their kids in 3 different ways:

  • x-linked – fathers who have the affected gene can’t pass it to their children. However, a mother who carries the gene can pass it down to her children (50 percent chance);
  • autosomal dominant – a parent with the gene has a 50 percent chance of passing it to each child;
  • autosomal recessive – both parents need to have the gene and each child has a 25 percent chance of being affected.

Risk Factors

Having a family history of RP increases the chance of developing a genetic disorder. But, some patients with retinitis pigmentosa have no family history of the disorder.

Diagnosis

RP is typically diagnosed during the teenage years, however, it may be present at birth.

There are special tests that can be used to detect retinitis pigmentosa:

  • electrophysiological test – it records the electrical currents which are produced by the retina due to a light stimulus;
  • dark adaptation test – it is usually done on an instrument called the Goldmann-Weekers adaptometer and measures how well your eyes adjust to changes in lighting;
  • color testing – it helps determine the status of the cone cells;
  • acuity test – it measures the accuracy of the central vision.

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Treatment

No medical treatment can reverse the damage caused by RP. However, some treatments can reduce the symptoms:

  • carbonic anhydrase inhibitors (such as – dorzolamide or acetazolamide) are given as eye drops or by mouth;
  • lutein and zeaxanthin (carotenoids that are found concentrated in leafy green vegetables) may slow the rate of vision loss;
  • omega-3 fatty acid supplements;
  • gene therapy – it is an experimental therapy that involves deactivating or replacing mutated genes which are causing RP;
  • vitamin A palmitate – it may help slow the progression of the disorder in some sufferers.

Important note – vitamin A toxicity can occur if taken at high dosages. Symptoms  of vitamin A toxicity include:

  • clumsiness;
  • liver problems;
  • dizziness;
  • blurred vision;
  • headache;
  • vomiting;
  • nausea.

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Bottom Line – Choroideremia vs Retinitis Pigmentosa

Choroideremia is a genetic condition that causes progressive loss of vision due to degeneration of the retina and the network of blood vessels behind the retina. The first symptom of this genetic condition is commonly an impairment of night vision, which can occur in early childhood. Night vision is followed by peripheral vision. Unfortunately, the field of vision slowly shrinks, affecting a patient’s central vision around age 45, and eventually leading to blindness.

Retinitis pigmentosa is an inherited disease in which the light-sensitive retina of the eye progressively and slowly degenerates. Individuals with retinitis pigmentosa experience a gradual decline in their vision because of the photoreceptor cells in the retina which degenerate. Symptoms can include:

  • difficulty in judging changes in peripheral vision, like – steps or curbs;
  • loss of peripheral vision;
  • problems seeing things in dimly lit environments;
  • poor night vision.

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References

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5757363/
https://www.ohsu.edu/xd/health/services/casey-eye/clinic
https://jamanetwork.com/journals/jamaophthalmology/article-abstract/628584