Retinitis pigmentosa

Retinitis pigmentosa

What is retinitis pigmentosa?

Retinitis pigmentosa (RP) is the name for a group of eye diseases in which the sensory cells in the retina gradually degenerate. This leads to severe vision loss over the course of time. Reasons for this are mutations: permanent alterations of the genetic material. Such genetic defects force the retina to synthesise erroneous proteins. This leads to disturbances of the cellular metabolism and, in the end, to the death of  photoreceptor cells. Retinitis pigmentosa affects approximately 30,000 to 40,000 people in Germany alone; worldwide there are approximately 3 million people living with this condition1.

Scientists have identified more than 80 different genetic mutations that can cause retinitis pigmentosa2. That is also the reason why the course and severity of the disease can vary strongly in individuals. Commonly, retinitis pigmentosa commences with the loss of the rods in the periphery of the retina, which are responsible for our low-light and night vision. This loss of night vision is therefore a first indicator of the disease, which often starts in the early youth. With the disease progressing further the visual field gradually decreases, usually from the periphery inwards. In contrast to the rods, the cones that are primarily located in the centre of the retina are not affected until the later stages. Many affected patients therefore do not completely lose their vision. What remains in the end stage of the disease, however, is typically a very small visual field directly in the line of vision (tunnel vision), which is also called tubular vision, since it resembles the view through a very narrow tube. Eventually the ability to recognise contrast and colours decreases as well. 

Images of the narrowing of the visual field in retinitis pigmentosa
Possible course of vision loss in retinitis pigmentosa (RP). In the course of the disease, the field of vision narrows more and more to tunnel vision. Source: © Okuvision GmbH.

Retinitis pigmentosa is a hereditary condition. This means that people who are affected can pass it on to their children. The disease can be triggered by a great variety of genetic defects and inheritance patterns, which in turn have a strong influence on its course and severity. Careful genetic counselling can help patients to understand the likelihood of passing on RP to their children.

What are the symptoms of retinitis pigmentosa?

Retinitis pigmentosa involves the loss of sensory cells in the retina, starting with the so-called rods, and followed later by the cones. This causes the increasing loss of retinal function, which leads to the typical vision impairment, including, for example:

  • Gradual narrowing of the visual field, ending in tunnel vision
  • Restricted ability to see in twilight or at night
  • Glare sensitivity
  • Impairments of contrast and colour vision

The type of symptoms and their sequence and severity depend on the areas of the retina that are affected by the loss of sensory cells.

What is the course of retinitis pigmentosa?

Typical for RP is a slow, sometimes staged, but steady progression. Systematic examinations show an exponential decrease of the visual field. On average, the remaining visual field of an RP patient decreases by half every 4-5 years.

 

Curve for limitation of the visual field of an RP patient

 

 

 

 

 

 

 

Exponential decrease of visual fiedl area in retinitis pigmentosa (Massof and Finkelstein, 1987).

Most people affected by RP realise this already at an early age, for example through night-blindness, in which the vision in low light and darkness are strongly impaired. Night-blindness is related to the early degeneration of the rods, the photoreceptor cells in the retina responsible for low-light vision.

Although in retinitis pigmentosa the rods are affected first, the disease will spread to the cones as it progresses further. These are responsible for colour vision and contrast distinction. When the cones start to become affected, this leads to impairment of colour vision of blue and yellow tones in the first instance. At the same time the contrast distinction is deteriorating with dark areas appearing overly bright. This contributes to an increased glare-sensitivity.

In the final stage of the disease, those affected can go completely blind. There are currently no therapies available to prevent and cure retinitis pigmentosa. Several so-called neuroprotective strategies are being researched to combat the degeneration of photoreceptors and other cells of the retina and to limit the loss of vision4.

The therapy of transcorneal electrical stimulation (TES) aims at slowing down the decrease of the visual field by electrical stimulation of the retina.


SOURCE:

  1. Retinitis pigmentosa. Online-Information der PRO RETINA Deutschland e.V. www.pro-retina.de/netzhauterkrankungen/retinitis-pigmentosa/krankheitsbild
  2. Verbakel SK, van Huet RAC, Boon CJF, den Hollander AI, Collin RWJ, Klaver CCW, et al. Non-syndromic retinitis pigmentosa. Prog Retin Eye Res. 2018;66:157-86.
  3. Massof RW, Finkelstein D. A Two-stage Hypothesis for the Natural Course of Retinitis Pigmentosa. Advances in the Biosciences. 1987;62:29-58.
  4. Pardue MT, Allen RS. Neuroprotective strategies for retinal disease. Prog Retin Eye Res. 2018;65:50-76