Retinitis pigmentosa (RP) is a disease that involves the eyes and affects the retina, a thin piece of tissue at the back of the eye. It occurs in 1 in every 3500 to every 1 in 4000 people in the United States. RP is also a complex set of heterogeneous congenital disorders that involve cell death (apoptosis) of photoreceptors in the retina namely the rods and cones.
Rods are responsible for dim lit visions as they are very sensitive to light that is why they enable us to see at night only in black and white and they do not distinguish color,
the cones, however, are responsible for colors. Found at the outer ends of the retina are the rods which are used in peripheral or side vision. Cones are located in the middle of the retina allowing us to perceive details and color.
How will the eye capture images? Light rays enter through the cornea (a domelike structure covering the iris), pupils and lens. These light rays are focused directly on the retina, which is the light-sensitive tissue lying posteriorly in the eye. The retina transforms light rays into electrical impulses sent to the optic nerves then to the brain where they are recognized as pictures or images. 70% of the focusing power of the eyes comes from the cornea and 30% comes from the lens.
Patterns of Inheritance
Retinitis pigmentosa is caused by one or more than 100 defective genes that cause the death of cons and rods in the retina. The following are patterns of inheritance that are linked to retinitis pigmentosa.
Autosomal dominant pattern
This is the least common with an onset in childhood which makes it more severe. It is associated with RHO gene which produces rhodopsin. The dominant genes contain or carry the code that has the retinitis retinopathy. When this is copied there is a 50 percent chance that the child will manifest the symptoms of having the disorder
Autosomal recessive pattern
This is the most common type with an onset in adulthood. It had a variable penetrance and associated with USHA2 that produces usherin, which is a basement membrane protein needed by the retina.
In this form, both parents are healthy but have the gene, therefore each of their children has the higher chance of inheriting one gene and can be a carrier. Each parent has a recessive gene that carries the code for the RP, even though they do not manifest the condition, they are considered to be carriers. When both parents pass their recessive gene onto their baby, there is a 25% chance that the child will have retinitis pigmentosa.
The genes responsible for this condition is located on X chromosomes. If the mother only carries the problem gene, the children will have a 50 percent chance of having the retinitis pigmentosa. If the father carries the recessive gene that has the RP, it will not be passed down to their sons.
Retinitis pigmentosa is not acquired by a specific disease or an injury, the child inherits it. The genes that are passed down to their offspring have a code containing the genetic information and some have the code needed in the development of the eyes like the protein needed by the photoreceptors. Mutations in the cells can cause discrepancies and this may alter the structure of the eyes and its function.
The onset of the manifestations (s/s) can be from infancy to middle adulthood. In RP, rod death precedes cone deaths so patients will present with the following symptoms.
This is the hallmark symptom of RP. This is the difficulty with nighttime vision or the difficulty seeing in dimly lit room. There is a decreasing or losing of vision at night like for example, the client takes time to adjust to the darkness and so he or she might stumble over objects, might find difficulty in driving especially at night, or watching movies at the theaters.
The peripheral vision (side vision) is a gradual loss. As the client moves around, he/she bumps into things because the visual field has already narrowed. There are times that the client is unable to see what’s below or around him or her.
This is often described by patients as bright light flashes.
There is the loss of central vision. Problems arise like difficulty threading the needle or reading difficulty. There is the lack of ability to distinguish colors.
Upon the examination of the fundus, there is the presence of vitreous cells, clumps of pigment in the side of the retina in a bone spicule arrangement, narrowing of the arterioles, areas of depigmentation and waxy disc pallor; Another manifestation that signals cone death is the bullseye maculopathy.
As the rods start to die before the cones, the client will usually maintain visual acuity even when the manifestations begin to appear.
There are different tests to help the physician diagnose the patient. The ophthalmologist will assess the eye using the ophthalmoscope.
- The ophthalmoscope will allow the doctor to see the structure of the eyes. A patient who has retinitis pigmentosa has dark spots on their retina.
- Electroretinogram (ERG) is the most definitive diagnostic test for RP. This is an electrical test that tells how the retina is functioning. Here, they have to dark adapt the eye meaning staying in the dark room for 20 minutes to test the rods. A contact lens is placed on the cornea holding the electrodes that are attached to the eyelid and at the earlobe. It uses a gold film to cover the eyes specifically lens and flashes of light will be illuminated at the entire retina. The doctor will measure the response of the retina to the light that is present and record the voltage change during the entire test.
- Visual field test. This test will measure the visual field of the patient. The patient will be instructed to look at the spot, an image will be displayed on the screen and when the patient sees the image he is required to press the button.
- Genetic test. A sample of your DNA will determine if you have the gene that causes the retinitis pigmentosa. Having a relative who has this condition can add the risk of having the RP.
There are conditions or syndromes associated with retinitis pigmentosa which require some laboratory tests to detect such features.
- The Venereal Disease Research Laboratory (VDL) test and Fluorescent treponemal antibody absorption (FTA-ABS) are done as studies for tertiary syphilis (for older clients-50-60 years old).
- Usher’s syndrome is one of the most common syndromic causes of RP where it is associated with hearing loss and problems with It comes from a defect from the inner ear.
- Waardenburg’s syndrome causes auditory hearing loss and abnormal pigmentation of the hair, skin, and eyes. People with this feature often have pale blue eyes or different color of the eyes like one eye is blue and the other one is brown (heterochromia iridium); there is also a distinct color of hair meaning there’s a patch of white hair or the hair turns gray early; and broad nasal root.
- ECG for Kearns-Sayre syndrome to help disregard heart block, and checking of the lipid profile with possible protein electrophoresis for abetalipoproteinemia (an inherited condition affecting the malabsorption of dietary fats).
- Bardet- bile syndrome affects many parts of the body like the eyes. There is vision loss which occurs as the tissue that sense light at the back of the retina gradually deteriorates and leads to RP. Clients with this type of syndrome advances to having poor visual acuity and can become legally blind in adolescence period or early adulthood because of the loss of central vision. Other symptoms of this syndrome include abnormal weight gain; high blood pressure, high cholesterol, polydactyly (having extra fingers or toes); with learning problems, kidney problems, infertile, dental abnormalities, and also emotional immaturity.
- For Cancer-associated retinopathy or severe RP, neoplasm (abnormal growth of tissue) related studies for antiretinal antibodies are needed.
As of today, there is no known direct cure for retinitis pigmentosa, but there are some medications and treatments that can inhibit or slow down the process of the progression of the loss of vision.
Vitamin A palmitate
This drug can slow down the process of the RP. This medication can be detrimental to the health of the person when the doses are not exact.
In time swelling is present inside the eye, this is called macular edema, this drug can reduce the inflammation and swelling to prevent the progression losing the sight.
The use of sunglasses can protect the eyes from the extreme light and ultraviolet rays during the day.
There is also a surgery that can be done as an option if the patient’s eyesight is worsening.
The retinal implant has a device that is in the eye that helps the patient see larger letters and objects, it is paired with a special glasses that help the device on the eyes.
Retinitis pigmentosa takes several years to progress. The percentage of the visual acuity of the eyes of the patient will decrease. Proper supportive treatment is given to the patient for him to experience a better quality of life.
Researchers are now being conducted to help minimize the progression of retinitis pigmentosa like stem cells but now people who have this condition would eventually have to register as legally blind to be able to be protected by the law and to have the benefits that the government is providing.