Retinitis pigmentosa (RP) is a group of rare hereditary diseases in which the retina slowly and progressively degenerates.
In the end, blindness can occur.
There are two main types of cells in the retina:
- The cones are located everywhere in the retina.
The center of the retina (the macula) contains the largest number of cones and allows central vision, reading and color discrimination.
- The rods are located everywhere in the retina, except in the center (visual pit).
The rods are used for night vision and vision in the periphery.
People with retinitis pigmentosa suffer from a gradual decline in vision because both photoreceptive cell types (cones and rods) die.
Types of retinitis
Autosomal dominant retinitis pigmentosa
If one parent suffers from the dominant form of retinitis, there is a 50% chance of passing the disease on to the children.
The autosomal dominant RP affects men and women equally.
Autosomal recessive retinitis pigmentosa
Both parents are healthy carriers and have a 25% chance of passing the disease on to a child.
Autosomal recessive RP affects men and women in the same way.
X-linked retinitis pigmentosa
In a healthy carrier and a healthy man, there is a probability of:
- 25% to have sick sons.
- 25% to have healthy carrier daughters.
- 50% healthy children (boys or girls) who are not carriers.
This is an inheritance pattern that mainly affects men. Female family members are carriers of the defective gene, but rarely get sick.
Sporadic retinitis pigmentosa
In about 30%, the child has been affected by retinitis pigmentosa since birth, although both parents are healthy. In these cases, the genetic defect occurs at the moment of sperm or egg cell formation.
Atypical retinitis pigmentosa can first:
- meet central vision (inverse RP) or
- vision in a single quadrant (sectoral RP).
RP sine pigmento has all the classic symptoms of the disease, with the exception of retinal pigmentation.
There are non-hereditary forms of retinal degeneration that lead to a reduction in the field of vision, similar to retinitis pigmentosa. They are called pseudoretinitis pigmentosa and can be of the following nature:
- Infectious – provoked by infection, the microorganisms responsible can be bacteria (in the case of syphilis), fungi (for example, Candida), a virus (such as the measles virus, cytomegalovirus or herpes virus) or protozoa (in the case of toxoplasmosis).
- Toxic – associated with the use of drugs such as: chloroquine, thioridazine, chlorpromazine, indomethacin, tamoxifen.
If treated early with antibiotics or antifungals, they can be cured without consequences, but waiting too long could cause permanent vision damage.
However, in these cases, vision impairment is stable over the years.
Causes of retinitis pigmentosa
There are many genes that can cause a change in the functioning of retinal cells and, accordingly, many different types of RP.
Retinitis pigmentosa is often mentioned along with other eye diseases with similar genetic causes and effects on vision, such as:
- congenital amaurosis after liver,
- cone-rod dystrophy,
RP may also be associated with other problems, such as hearing loss.
These rare circumstances are called associated RPs or syndromes.
Syndromes of retinitis pigmentosa
In most cases, the genetic defect affects only the eyes. Sometimes other parts of the body are also affected. For example, patients with Usher syndrome develop a combination of deafness and blindness.
How to inherit retinitis pigmentosa?
There is an important genetic component in retinitis pigmentosa.
Symptoms of retinitis pigmentosa
Because retinitis pigmentosa is a progressive condition, the signs and symptoms worsen over time. The first symptoms that are noticed are:
- poor night vision or night blindness;
- vision problems in poorly lit environments;
- Loss of peripheral vision (lateral) or limitation of field of vision;
- Difficulty assessing changes in the lateral field of vision, such as curbs or steps.
- Loss of visual acuity.
Course or evolution of retinitis pigmentosa
The most common sign in all forms of retinitis pigmentosa is gradual degeneration of the cones and rods.
Most forms of RP first cause degeneration of the rods.
These forms of RP, sometimes called rod and cone degeneration, usually begin with night blindness.
Night blindness can be thought of as what usually happens when you enter a dark cinema on a sunny day.
Patients with RP cannot see well in dark and poorly lit environments.
As the disease progresses, more rods degenerate, patients lose peripheral vision.Patients with RP often have a tubular field of vision or tunnel vision, as if they were seeing the environment through the opening of a straw.
Many patients with RP retain some degree of central vision throughout their lives.
Patients notice partial loss of central vision that cannot be corrected by glasses or contact lenses.
With the loss of cone cells, the disturbances in color perception begin.
As the disease progresses, the rods degenerate, causing peripheral vision loss.
At what age does retinitis pigmentosa occur?
There is no specific period of time for onset, symptoms can begin in childhood or after the age of 40.
The symptoms of RP are usually seen in children, adolescents and young people.
Diagnosis of retinitis pigmentosa
These specific tests can be used to diagnose RP:
Examination of the fundus of the eye
These examinations are used to evaluate the appearance of the retina, pupil and blood vessels in the eye. At the beginning of the disease, they may look normal, as the disease progresses, certain changes can be noted:
- pupillary pallor,
- Thinning of the optic nerve capillaries.
- Pigmentation of the retina.
Visual acuity tests
These examinations measure the accuracy of central vision at certain distances and certain light situations.
This can help to determine the status of the cone cells, i.e. the cells that evaluate the colors.
Test of the visual field
This test is performed using a peripheral vision measurement device.
Test of adaptation to darkness
This test measures the ability of the eyes to adapt to changes in lighting and can help the doctor better study the functioning of the rods, which are the cells in the retina responsible for night vision.
The ERG (electroretinogram) registers the electrical signals generated by the retina as a result of a light stimulus. The intensity and rapidity of the electrical signal decrease with the degeneration of the photoreceptors.
OCT (Optical Coherence Tomography)
This procedure is helpful for closely examining the structures and tissues of the retina.
Retinography allows photographic documentation of the retina to evaluate its state of health.
This examination is helpful in revealing the earliest retinal changes, determining the nature of the damage, and assessing the condition of the eye’s blood vessels.
What is the therapy for retinitis pigmentosa?
There is no definitive treatment for retinitis pigmentosa.
However, there are some treatment options, such as avoiding light and/or using vision aids to delay the progression of RP.
There are some experimental devices and the first results in patients are quite promising.Argus II Retinal Prosthesis System
Second Sight Medical Products has developed the Argus II Retinal Prosthesis System for patients with severe retinitis pigmentosa and other degenerative retinal diseases.
The Argus II system consists of a small video camera built into special eyeglasses.
The camera is connected to a small wireless device worn by the patient.
The device converts the incoming video pulses into electrical signals that are transmitted wirelessly to the implant in the eye.
The implant uses the information to stimulate the remaining healthy cells of the retina and the visual information is transmitted via the optic nerve to the brain, where it is perceived as light patterns.
The patient learns to interpret these models in such a way that he can distinguish the contours of objects.
According to published studies, all patients have received some visual perceptions from the Argus II device, many have shown significant improvements in their movement, such as following lines, opening doors and windows, and dodging objects.
There are people with an Argus II implant who have been able to read short sentences, exceeding researchers’ expectations.
Vision improvements were maintained in many patients over a follow-up period of at least two years.
Gene therapy treatment
Protection factor CNTF
The researchers from the University of Oxford, in collaboration with the University of Florida and the University of Western Australia, are currently testing a protective factor of photoreceptors called CNTF.
The goal is to prolong the life of retinal cells with altered genetic code that leads to self-destruction.
Currently (2017) eye drops containing nerve growth factor (NGF) are being tested.
The protein discovered by Rita Levi-Montalcini plays a fundamental role in the regeneration of neurons and tissues.
Food supplements and nutrition for retinitis pigmentosa
Antioxidants may be useful in treating patients with RP, but there is no clear evidence of the benefits of vitamin supplements.
Some patients report improvements in macular degeneration with fenretinides, which are a derivative of vitamin A.
Docosahexanoic acid (DHA)
DHA is an omega-3 polyunsaturated fatty acid and an antioxidant.
Studies have shown an association between the amplitudes of the electroretinogram and the concentration of erythrocyte DHA in patients. Other studies show a tendency for minor changes in ERG in patients with elevated DHA levels.
Macular edema can reduce vision in advanced stages of retinitis pigmentosa.
Of many proven therapies, orally administered acetazolamide has shown very satisfactory results with some improvement in visual function.
The studies by Fishman et al and Cox et al have shown an improvement in visual acuity with oral acetazolamide in patients suffering from RP with macular edema.
Lutein and zeaxanthin are macular pigments that the body cannot produce itself, but must be ingested from food sources.
Lutein helps protect the macula from oxidative damage and supplements have shown an increase in macular pigments.
The benefit of orally administered valproic acid has been demonstrated in clinical trials, and other larger clinical trials are ongoing.
Drugs with possible side effects in retinitis pigmentosa
A drug used to treat acne has been known to be an active ingredient that worsens night blindness.
A drug used to treat erectile dysfunction has been identified as a cause of changes in ERG and reversible vision problems.