What forms of retinitis pigmentosa are there?
As already mentioned at the beginning, retinitis pigmentosa is basically a collective term for a variety of diseases in which similar processes occur. The classification is sometimes different in different works of technical literature, but basically one can distinguish between three groups of Retinitis pigmentosa: In addition to these three basic forms, there are other forms of retinitis pigmentosa that cannot be clearly assigned to one of these groups. These include the extremely rare treatable forms of retinitis pigmentosa: atrophia gyrata, Bassen-Kornzwei syndrome (also known as abetalipoproteinemia) and Refsum syndrome.
Here, good cooperation with a metabolism and nutrition specialist is essential in order to be able to control the disease.
- Primary retinitis pigmentosa
- Associated retinitis pigmentosa
- Pseudo-retinitis pigmentosa.
The symptoms and processes in the eye treated in the text so far are primary retinitis pigmentosa, from which 90% of those affected suffer. The exact genetic causes underlying this disease have not yet been sufficiently researched.
Until now, it has only been possible to establish that various changes in the genetic make-up and various protein defects are present in those affected. Thus, the course of the disease can be quite different from person to person, only the final stage with the complete loss of the photoreceptors of the retina is identical for all of them.If retinitis pigmentosa does not occur alone, but patients suffer from other symptoms that are not related to the eye, it is called associated retinitis pigmentosa, usually as a partial symptom of a syndrome. Frequently occurring concomitant diseases can be Hearing problems, muscle weakness to muscle paralysis, walking disorders, growth disorders, problems with highly scaly and light-sensitive skin, a mental disability, congenital cystic kidneys and/or heart malformations and cardiac arrhythmia.
The two most frequently occurring syndromes are the so-called Usher syndrome and the Bardet-Biedl syndrome. Pseudo-retinitis pigmentosa or phenocopy, on the other hand, is when the patients show the typical symptoms of primary retinitis pigmentosa described above, but no hereditary components can be identified, and the destruction of the retinal cells was caused by other diseases. This can be the case, for example, with autoimmune diseases, inflammation or even poisoning (by poisons or even by drugs or other substances).
Among the characteristic symptoms that occur are The severity and the order in which the symptoms occur can be different for each person. In retinitis pigmentosa, the visual field is gradually reduced due to the destruction of the visual cells. Typically, it narrows more and more from the peripheral areas until only a small remnant of visual cells is left at the very center.
This is usually referred to as “tunnel vision” or “tube vision”. The name alone illustrates quite well, even to the non-affected, how this form of limited vision can be imagined. The visual acuity, on the other hand, can still be reasonably good, so that there are people who need aids such as a blind person’s wand to cope with everyday life, but are still able to read a newspaper or a book.
Unfortunately, this combination often leads to the assumption in healthy people that those suffering from retinitis pigmentosa are only simulating their visual impairment. It is also not uncommon for those affected to become aware of the limitations of their visual field only after an incident or even an accident, since the brain is very well able to compensate for failures in the visual field and to calculate a good image of the surroundings despite everything. In many patients with retinitis pigmentosa, however, the failures manifest themselves quite differently, for example as a circular ring around the focal point (a so-called ring scotoma) or as differently distributed black spots.
Rarely, but in principle also possible, is a beginning of the visual field failures in the center, at the place of the macula (place of sharpest vision in the retina). Those affected then need aids such as magnifying glasses and the like at a very early stage in order to be able to recognize objects sharply, while the orientation in space is still relatively well preserved. Since in retinitis pigmentosa the rods are affected before the cones, the symptom of night blindness occurs much earlier than the loss of visual field.
For the patient, this means that he or she is almost blind at night and dependent on help, whereas with sufficient light he or she does not notice any major limitations. As soon as the cones are also affected, the described failures in the visual field and increased light sensitivity occur, patients are quickly dazzled and darker parts of the image are outshined by brighter ones. This is due to the fact that the perception of contrast in the human eye only comes about through the interaction of adjacent cones.
However, if these are damaged, not only color perception is impaired, but also contrast perception. This symptom is further aggravated by glaucoma, which often occurs in patients suffering from retinitis pigmentosa. The lens becomes cloudy and is no longer able to bundle the incoming light properly, but rather scatters it, which further enhances the glare effect.
Since in retinitis pigmentosa the rods are affected before the cones, the symptom of night blindness occurs much earlier than the loss of visual field. For the patient, this means that he or she is almost blind at night and dependent on help, whereas he or she does not notice any major limitations when there is sufficient light.As soon as the cones are also attacked in the further course of the procedure, the described failures in the field of vision and increased light sensitivity occur, patients are quickly dazzled and darker parts of the image are outshone by lighter ones. This is due to the fact that the perception of contrast in the human eye only comes about through the interaction of neighboring cones.
However, if these are damaged, not only color perception is impaired, but also contrast perception. This symptom is further aggravated by glaucoma, which often occurs in patients suffering from retinitis pigmentosa. The lens becomes cloudy and is no longer able to bundle the incoming light properly, but rather scatters it, which further enhances the glare effect.
- The narrowing and loss of the visual field
- The night blindness or even at light twilight reduced vision
- Photosensitivity
- A disturbed color perception and
- A noticeably longer period of time until the eyes have adapted to different light conditions and contrasts
To date, there is still no cure for retinitis pigmentosa. Some studies indicate a slightly slower course of the disease when vitamin A is taken. Others consider hyperbaric oxygen therapy to be helpful.
Gene therapy approaches and stem cell therapies that attempt to attack the disease at its cause, the defective genes, are currently only being researched and have not yet been tested. Also under discussion are retinal implants that are intended to serve as prostheses. In people suffering from retinitis pigmentosa, many of the functions of the eye or retina already described are no longer possible due to the destruction of rods and cones.
The light receptors gradually die off during the course of the disease, usually affecting the rods first and then the cones. Depending on where the destruction of the receptors is most severe, various failures of the visual field and different functional failures can occur. In most cases, Retintis pigmentosa is caused by hereditary or spontaneous mutations of certain genes, which lead to a degeneration of the retina or the rods and cones.
If the retinitis pigmentosa is not based on a hereditary component, it is also known as pseudo retinitis pigmentosa, in which case the photocells are also destroyed. Triggers are e.g. autoimmune diseases or inflammatory processes. Anyone who discovers that they have Retinitis pigmentosa will sooner or later probably ask themselves the question of whether this disease is hereditary, or with what certainty the causative genes will be passed on to the offspring.
The number of genes that can lead to the development of retinitis pigmentosa is not certain. So far, more than 45 genes have been identified where mutations could be the cause of the disease. Before statements can be made about the probability of inheritance, an exact diagnosis must be made, which involves a genetic examination.
In general, it can be said that more than 50% of all patients suffering from retinitis pigmentosa give birth to children with completely healthy eyes (here it is assumed that only one of the two parents is affected). The remaining 50% have a 50% chance of having healthy children. However, a 100% safety for a healthy child cannot be predicted.
The disease can be based on different gene mutations as well as on different inheritance processes. However, the majority of the genes discovered so far follow a monogenetic inheritance. This means that the harmful mutation is restricted to a single gene and does not affect several. The hereditary factors can be passed on autosomal-dominantly, autosomal-recessively as well as gonosomally (mostly it is the X-chromosome).
