Retinitis pigmentosa (RP)
What is retinitis pigmentosa?
With a morbidity rate of 1 per 4000 people, retinitis pigmentosa is the most common form of all hereditary, non-inflammatory retinal diseases, whereas men are more commonly affected than women. It was first described in 1855 by the Dutch ophthalmologist, Franziscus C. Donders. In Germany, more than 40,000 people get RP per year and 1,000 people per year become blind from this disease.
This congenital, mostly hereditary disease is characterised by a (sometimes slow) progression of the demise of the sensory cells in the retina. This disease especially affects the rods, which are responsible for the perception of light and dark. The more often the rods fall prey to cell death, the more severe the symptoms. The pigment layer of the retina also increasingly loses its function. The cause of this disease is a defect in the receptor genes of the sensory cells. In the past 30 years, 20 genes have been identified which are responsible for the appearance of RP. The first discovery was a defect in the so-called Rhodospin gene, which is responsible for the production of photo pigments. Because in most cases both eyes are affected, RP patients suffer from an increasingly larger loss of vision.
How is retinitis pigmentosa recognisable?
One of the first signs of this illness is a loss of visual acuity in dark surroundings. This so-called night blindness with a slowed adaptation of the sensory cells to twilight and darkness, follows the narrowing of the field of vision. At the beginning, affected persons report a ring-formed loss in their field of vision; in later stages they describe their visual perception as looking through a telescope. A massive constriction of vision causing the pipe or tunnel vision, makes it increasingly difficult for patients to orient themselves in a room so that in the end they are practically blind. In the beginning, affected patients have problems adjusting to dark rooms (in a cinema, theatre, restaurant, or when they come out of daytime sunlight into a room) and trip over stairs, inadvertently kick things and bump into things with their knees because they can’t see them.
How can retinitis pigmentosa be diagnosed by the eye doctor?
- Storage of pigment (bone-spicule) accumulated in a retina affected by retinitis pigmentosa
In addition to the patient’s description of the symptoms mentioned above, as well as recurring signs through small injuries, the experienced ophthalmologist can make a diagnosis through the appraisal of the ocular fundus and therewith the retina and optic nerve. In the middle and outer retinal periphery, so-called bone-spicules are recognisable (dark clumps in the retinal pigment epithelium). In addition to the demise of further layers of the retina and the constriction of small retinal vessels, later stages of retinitis pigmentosa result in irreversible damage to the optic nerve. Myopia (nearsightedness) is also diagnosed by eye doctors in many RP patients. Further examination methods, such as the electroretinogram, show (even in early stages of retinitis pigmentosa) a ceased activity of the sensory cells. In the beginning, only the rods (responsible for light and dark vision) are affected by a loss of function and in further progression of the disease the cones (responsible for colour vision) are also affected. Common later consequences of RP are the development of cataracts and the appearance of retinal swelling in the macular area, which is the sharpest point of vision in humans.
What are the possible treatments for retinitis pigmentosa?
Basically retinitis pigmentosa currently cannot yet be healed. It is, however, possible to try slowing the progress of this disease, in order to keep a certain amount of vision throughout the patient’s lifetime. It has been proven in clinical long-term studies that the daily intake of vitamin A can marginally slow the decline of vision. At the moment, further experimental studies are looking at omega-3 fatty acids and growth factors for connective tissue cells (FGF-- fibroblast growth factor). These new approaches to treatment will perhaps give a new perspective to the successful treatment of RP in the future. In order to retain the remaining retinal function as long as possible, it is surely sensible to provide optimal and healthy care of the retinal metabolism. The combination of vitamin A, antioxidants (e.g. vitamins C and E) and lutein in the form of capsules or tablets can serve as valuable support. Treatment of the symptoms should naturally be mentioned as well, for example such measures as operating on cataracts, treatment for macular swelling, sunglasses to reduce glare, as well as reductive visual supports which enlarge the visual field (it sounds paradoxical but is in some cases useful!). Self help groups and early intervention groups provide great support and help in dealing with illness and learning practical skills for the patient him/herself as well as for parents and immediate family members of the RP patient.
Which check-ups are important for retinitis pigmentosa?
It is immensely important to have frequent check-ups in order to enable an optimal and individually suited treatment. Regularly determining the current visual acuity and glasses prescription as well as the exact appraisal of the ocular fundus and the documentation of changes is the basis of RP treatment. Further, it is important to have an examination of the field of vision at least once a year, in order to make an exact judgment of the patient’s visual constraints. Administering an electroretinogram to check the function and sensory cells (rods and cones) as well as the determination of the threshold adaptation to dim and/or dark surroundings, are supporting diagnostic measures in the course of this hereditary retinal disease.
Subretinal chip implantation: Music of the future?
- Ocular fundus of an RP patient after implant of a photo chip under the retina
Currently, the implant of a retinal prosthetic in the form of an electronic chip is at the centre of retinal research, with the goal of giving blind persons a little of their lost vision back. In a several-hour-long operation, under general anaesthesia, the square-shaped microchip, about the size of a grain of rice, is placed near point of sharpest vision under the retina, where incoming light is converted into amplified signals, electrically stimulating the remaining functional sensory cells. By way of the optic nerve, this information ends up in the visual cortex of the brain where the visual images are then made conscious. A prerequisite for the function of the chip is however a normally functioning optic nerve. For this reason, the use of this technological innovation is currently reserved only for treating certain eye diseases that lead to blindness. Those affected by RP have first priority for the use of retina chips. The subretinal chip implant was performed on a human for the first time in 2005 within the framework of a pilot study, and has until now shown exceptionally positive and successful results. The blind participants in the study were able to recognise and to place light sources again, as well as to perceive light objects on dark backgrounds. With a future of large research efforts and the further development of current technology, one day many blind people will perhaps be able to realise their dream of seeing within a limited range again.
WEBSITE ADDRESSES
Funding and Associations
Verein Contrast (Vienna, Lower Austria, Burgenland):
www.contrast.or.at
ProRetina Deutschland:
www.pro-retina.de
Tiroler Blinden- & Sehbehindertenverband:
www.tbsv.org
Hilfsgemeinschaft der Blinden und Sehschwachen Österreichs:
www.hilfsgemeinschaft.at
Subretinal Chip Implants
Universitätsklinik für Augenheilkunde und Optometrie, Tübingen, Deutschland (Prof. Dr. E. Zrenner):
http://www.medizin.uni-tuebingen.de/kliniken/augen_kl/index.html
Universitätsklinik für Augenheilkunde und Optometrie, Graz
(Univ.-Prof. Dr. M. Velikay-Parel):
http://www.meduni-graz.at/augenheilkunde/
Interesting Links
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