Retinitis pigmentosa

Retinitis pigmentosa: description

Retinitis pigmentosa (retinitis pigmentosa) is a large group of genetically caused eye diseases, all of which lead to the creeping death of the visual cells in the retina (retina), ie the rod and cone cells. Visual disturbances up to blindness are the consequences. Mostly both eyes get sick; in rare cases, retinopathia pigmentosa affects only one eye.

Although it is one of the rarer eye diseases, retinitis pigmentosa is considered the most common cause of vision loss in middle-aged adults. Worldwide, about three million people suffer from it. In Germany, the number of those affected is estimated at 30,000 to 40,000. Retinitis pigmentosa affects women and men, both young and old.

The term “-itis” usually means inflammation in medical terminology. Retinitis is not retinal inflammation, but another form of retinal disease. The correct name is therefore Retinopathia, but the term retinitis has prevailed for this disease.

Forms of retinitis pigmentosa

When the disease begins in the course of life, how fast it progresses, and how severe vision loss will be depends on the genetic cause of the disease. There are various genes (genes), which can cause the disease in genetic modification (mutation). The numerous subtypes of retinitis pigmentosa are subdivided into three main groups depending on heredity:

• Autosomal dominant retinitis pigmentosa (frequency: 20 to 25 percent)
• autosomal recessive retinitis pigmentosa (frequency: 15 to 20 percent)
• X-recessive retinitis pigmentosa (frequency: 10 to 15 percent)

Read more about the three hereditary forms below in the section “Causes and risk factors”.

In addition, there are some special forms of retinitis pigmentosa, in addition to the typical vision problems cause even more discomfort such as hearing, tingling (nystagmus), lens cataract (cataract) or morbid obesity. The main groups are:

• congenital hepatic amaurosis (frequency: 4 percent)
• Digenic retinitis pigmentosa (frequency: very rare)
• Usher syndrome (frequency: 10 percent)
• Bardet-Biedl syndrome (frequency: 5 percent)

An early diagnosis of the particular form is important to ensure individual treatment. This also applies to eye changes that often occur with retinitis pigmentosa. For example, cataract develops in about half of those affected and accelerates vision loss if left untreated. The slow blindness also strains the psyche of those affected. Depression is not uncommon and should be early detected and treated to improve quality of life.

Retinitis pigmentosa: symptoms

Common to all forms of retinitis pigmentosa is the fact that the retinal cells responsible for vision (rod and cone cells) gradually die off.

Rod cells are found predominantly in the periphery of the retina. They enable people to see at night or twilight, as they react to light of the lowest intensity and transmit this information to the brain. There, the impulses are processed in a complex way, so that the human being is able to distinguish between about 500 shades in the dark.

Zapfenzellen are predominantly located in the center of the retina and allow humans the color vision in the day and the sharp eye.

The symptoms of retinitis pigmentosa can be attributed to the gradual dying of the two cell types:

• progressive night blindness (usually the first sign)
• increasing tunnel vision (early sign)
• increased glare sensitivity
• decreasing color vision
• disturbed contrast vision
• prolonged adaptation time of the eyes, for example when switching from a light to a dark room quickly
• insidious loss of visual acuity
• complete blindness

Retinitis pigmentosa: night blindness

In many cases of retinopathy pigmentosa, the rod cells die first, and later the cone cells. Night blindness is therefore usually the first sign: those affected become increasingly disoriented in the dark. They also find it difficult to adjust their eyes to a rapid change from light and dark (for example, from the sun to a dark room).

Retinitis pigmentosa: visual field restriction

The visual field restriction manifests itself depending on the form of retinitis pigmentosa. The visual field often narrows from the outside inwards to the tunnel view. In other cases, failures around the center or patchy over the entire field of view are possible. Less often, the affected person loses his field of vision from the inside out.

Retinitis pigmentosa: color vision and photosensitivity

After the death of the rod cells, the cone cells gradually lose their function. Concerned people perceive colors less well, they are less able to differentiate between contrasts and they are progressively more susceptible to glare. In the final stage of the disease it comes often to complete blindness.

Retinitis pigmentosa: other symptoms

In addition to these symptoms, there are also typical signs of Fundus:

• Narrowing of the blood vessels
• waxy yellow papillae
• Changes of the macula lutea (“yellow spot”)
• Pigment deposits (“bone corpuscles”)

In addition, changes are known that affect the vitreous of the eye:

• lens opacity
• Drusenpapille (lime deposits in the optic nerve head)
• Myopia
• Keratoconus (corneal deformation)
• inflammatory vasculopathy (vascular disease)

The last two symptoms (keratoconus and inflammatory vasculopathy) are rare in retinitis pigmentosa.

Retinitis pigmentosa: causes and risk factors

The cause of retinitis pigmentosa can only be found in the genetic material. Four aspects play a role, which are responsible for the many sub-forms and thus the course of the disease:

• To date, more than 100 genes are known (main groups and special forms), which lead to damage (mutation) to one of the many sub-forms.
• There are several thousand different mutations in these genes.
• Different mutations on one and the same gene can cause different subforms.
• One and the same mutation on a gene can lead to different clinical symptoms.

The previously known genes encode proteins that are essential to mechanisms of vision: phototransduction (transformation of the light stimulus), metabolism of the retina, genetic processes (RNA splicing), development and maintenance of tissue, cell structure. At the beginning of the disease, therefore, only the respective process is disturbed. In the advanced stage, however, the common consequence is the death of the visual cells.

Retinitis pigmentosa: Why do the cone cells die?

So far, the question of why the rod cells are dying off after the death of the rod cells has not yet been completely clarified. Because only the cell death of the rod cells is (in most cases) genetically determined. Various factors may also contribute to the death of the cone cells, including oxidative stress, lack of energy or special proteins (such as RdCVF). For example, RdCVF is delivered by rod cells, so that cone cells can take up vital glucose for energy. If rod cells die, RdCVF is lost and cone cells lack the necessary energy to survive.

Retinitis pigmentosa: Three hereditary forms

A mutation can be inherited from one generation to the next (because it is already present in the father and / or mother) or it “comes into existence” when the paternal and maternal genetic material mix together after fertilization of the egg and sperm cells. A damaged gene may or may not necessarily lead to the disease. This depends on whether the gene is dominant or recessive and on which chromosome it sits.

Each person has 22 pairs of chromosomes (autosomes) and two sex chromosomes (gonosomes): One woman carries two X chromosomes, one man carries an X and a Y chromosome. The woman’s pair of chromosomes and two X chromosomes are homologous, meaning that they each have the same genetic information (one copy from the father, one from the mother). Each gene is therefore available in duplicate.

The transmission of genes on the autosomes is called autosomal inheritance. If a mutated gene is dominant, only one copy has to be damaged and the disease breaks out because it prevails against the existing healthy gene copy (autosomal dominant inheritance).

In the autosomal recessive inheritance both gene copies must be mutated to trigger retinitis pigmentosa.

A special case is the so-called X-recessive inheritance dar: The damaged gene is here on the X chromosome and is recessive. In women, the healthy gene copy on the second X chromosome can prevent a disease outbreak. As a gene carrier, however, they can pass on the disease to their children. Men, on the other hand, who have only one X chromosome, always fall ill with the X-recessive variant.

Retinitis pigmentosa: Genetic counseling

The probability of passing the retinitis pigmentosa on to one’s own children depends on the hereditary pathway, whether the mutated gene is dominant or recessive and whether the father or mother is the gene carrier. For sufferers or family members of sufferers, detailed genetic counseling is often important for family planning. As a rule, one of the ophthalmologists clarifies the probabilities of heredity. Even self-help associations such as Pro Retina Germany e.V. advise in detail on the Augenankankung.

Retinitis pigmentosa: examinations and diagnosis

The ophthalmologist can tell if anyone has retinitis pigmentosa by using different methods. Before he starts his eye exam, he inquires about the nature of your symptoms, how long they have existed, and whether family members are also suffering from retinitis pigmentosa. Possible questions are:

• Do you have trouble seeing in the dark?
• If so, since when do you see worse in the dark?
• Is there someone in your family who is slowly going blind?
• If so, are only siblings affected or did the disease appear in previous generations?
• Does an item get sharper if you do not look at it directly, but just pass it by?
• Is your field of vision restricted, for example through blotchy areas or through narrowing from the outside?

In addition, the doctor interviews you about possible other causes of vision problems. For example, drug poisoning, tumor diseases or other retinal diseases such as congenital night blindness lead to similar symptoms as retinitis pigmentosa.

Functional diagnostics

In the next step, the doctor tests your eyes for the following visual performance:

• Visual acuity (with an eye test)
• Color vision (usually with the Lanthony Panel D-15 desaturated test)
• Visual field (usually with a so-called perimeter such as the Goldmann perimeter)
• Adaptability from light to dark (with a dark adaptometer)

General eye exams help the doctor to check your eyes for typical changes such as increased pigmentation of the retina, narrowing of the blood vessels or clouding of the lens.

Afterwards the physician examines the function of your retina. Using an electroretinogram (ERG), he measures the electrical potential that both the rod and cone cells emit when exposed to light. The more advanced the retinopathy pigmentosa, the less intense is the response of the cells to light.

In advanced cases, the ophthalmologist records the remnant function of the cone cells using the so-called multifocal ERG. In very advanced cases, the physician uses pupillography to determine the function of the pupil under different light conditions. However, only specialized centers offer this study, mostly in the context of scientific studies.

Genetic diagnostics

An important step in the diagnosis of retinitis pigmentosa is to identify the damaged gene using molecular diagnostics. For the molecular biologist who examines the genome for mutations, the results from the ophthalmology practice and a pedigree of the person concerned are helpful. Nevertheless, it can not be guaranteed that the corresponding gene change will be detected. Because it is believed that not all genes and mutations are known that can trigger a retinitis pigmentosa.

Retinitis pigmentosa: treatment

At the moment, retinitis pigmentosa can not be treated with a few exceptions (such as Atrophia gyrata, Bassen-Kornzweig syndrome). The treatment is therefore limited to alleviating the symptoms with:

• Glasses, contact lenses or magnifying vision aids
• UV protective glasses
• Cut-off filter glasses
• specialized computer software
• cane
• Orientation and mobility training

Furthermore, one treats complications such as cataract or changes in the macula lutea.

Often, the psychological burden under which people with retinitis pigmentosa have to suffer is underestimated. Since the disease is usually noticeable at an early age, it can severely impair the quality of life at an early stage. Frustration, anger, stress and anxiety and even depression are known complaints. To improve quality of life, timely diagnosis and treatment is recommended.

Retinitis pigmentosa: therapy in prospect?

For over two decades, scientists have been pressing for possible therapies for retinitis pigmentosa. Scientists are exploring ways to stop or completely prevent the disease. An attempt is made to correct the genetic defect, to prevent the death of the photoreceptive cells or to rebuild dead cells. Promising methods include:

• Gene therapy: replacement of the defective gene by a healthy (transfer into the cell via virus envelopes)
• Stem Cell Therapy: Stem cells that become retinal cells and replace dead cells
• Medications such as unoprostone isopropyl eye drops, QLT091001, valproic acid
• Cell protection: growth factors (such as CNTF) or factors that prevent cell death (such as DHA), or RdCVF, to prevent the death of the cone cells
• electronic or subretinal retinal implants: A light-sensitive chip implanted under the retina is intended to partially restore the function of the visual cells.
• Optogenetics: Gene technology integrates photosensitive channels or pumps into the photoreceptor cells to restore their function.

Many of these technologies are currently being researched – in the test tube, on animals and some already in humans. Affected persons therefore have the opportunity to participate in one of the current studies. There are some of them, but by no means all forms of retinitis pigmentosa. Therefore, not all those affected benefit from currently active studies.

Whether the additional administration of vitamin A has a positive influence on the disease is not yet clarified. Some studies speak against an effect. Only the Basse-Kornzweig syndrome can be stopped by the administration of high-dose vitamin A.

Retinitis pigmentosa: disease course and prognosis

The course of retinitis pigmentosa is progressive (progressive). That is, the symptoms of night blindness, narrowing of the field of vision, color blindness and sensitivity to blemishes are increasingly worsening to the point of blindness. An influence on the course, however, has the form of the disease: the X-linked recessive retinitis pigmentosa usually takes the hardest course, followed by the autosomal recessive and the autosomal dominant form. The latter generally has the best course.

Since there is still no cure, countless subtypes of retinitis pigmentosa with different courses exist and sufferers, but also relatives often feel left alone, detailed discussions with the ophthalmologist are highly recommended. An important contact point is also Pro Retina, a self-help association for people with retinal degeneration like Retinitis pigmentosa.