Retinitis Pigmentosa: What is it?
Retinitis Pigmentosa (RP) is a clinically and genetically heterogeneous group of inherited retinal disorders, characterized by diffuse progressive dysfunction of predominantly rod photoreceptors with subsequent degeneration of cone photoreceptors and the retinal pigment epithelium (RPE). Visual impairment usually manifests as night blindness and progressive visual field loss.
Retinitis Pigmentosa: Risk Factors
There are no known risk factors for Retinitis Pigmentosa other than genetic predisposition. Retinitis Pigmentosa may occur as an isolated sporadic disorder or be inherited as autosomal dominant, autosomal recessive, or X-linked. Many cases are due to a mutation of the rhodopsin gene. Retinitis Pigmentosa may also be associated with certain systemic disorders which are usually autosomal recessive. There are many genes associated with Retinitis Pigmentosa for which a patient can undergo genetic testing.
Retinitis Pigmentosa: Histopathology
Histopathologic studies suggest that RP results from a primary defect in the rod and cone photoreceptors. Pathologic findings of an enucleated eye in a patient with autosomal recessive RP showed that the rod and cone outer segments were shortened and disorganized in the patient’s best field of vision, while in the area of visual loss there was a total loss of outer segments and a decrease in photoreceptors number.
Two types of pigmented cells were found invading the retina: typical RPE cells that were migrating away from the retinal pigment epithelial layer, and macrophage-like cells that contained melanin.
Retinitis Pigmentosa: Pathophysiology
The pathophysiology of Retinitis Pigmentosa has been studied in several animal models. In the rat, retinal degeneration caused by the failure of retinal pigment epithelium to phagocytose the shed rod outer segment discs results in the accumulation of rod outer segment debris.
Retinitis Pigmentosa: Molecular genetics
that cause Retinitis Pigmentosa have been mapped or identified. Genes that cause RP can be categorized into those that affect the phototransduction cascade, the retinoid cycle, photoreceptor structure, or other biological function of photoreceptor and retinal pigment epithelium. The most frequent known causes are mutations in the rhodopsin (phototransduction cascade), USH2A (photoreceptor structure), or RPGR (maintenance of cilia or ciliated cells with a possible role in trafficking) genes.
Retinitis Pigmentosa: Symptoms
With Retinitis Pigmentosa, you may have vision loss in the following ways:
Loss of Night Vision. Night blindness is when you cannot see anything in the dark. Your vision may be normal during the day. As you start losing night vision, it takes longer to adjust to darkness. You may stumble over objects or have trouble driving at dusk and at night. You might also find it hard to see in movie theaters or other dim rooms.
Gradual loss of Peripheral (side) Vision. This is known as “tunnel vision.” You may find you bump into things as you move around. This is because you are not able to see objects below and around you.
Loss of Central Vision. Some people also have problems with Central Vision. This can make it hard to do detailed tasks such as reading or threading a needle.
Problems with color vision. Some people may also have trouble seeing different colors.
Retinitis Pigmentosa: Diagnostic procedures
Full-Field Electroretinogram (ERG): ERG measures the electrical potential generated by rods and cones after a light stimulus and is essential in the diagnosis of Retinitis Pigmentosa. The most important parameters being measured include a- and b-wave amplitudes and implicit times. In the early stages of the disease, there is a reduction in a- and b-wave amplitudes but implicit time can be prolonged or remain normal. Patients with advanced stages have non-detectable ERG.
Dark Adaptometry (DA): Visual threshold is the minimum intensity of light that will stimulate the rods or cones to elicit a subjective response. Dark adaptometry measures the absolute threshold of rods at given time intervals as the retina adapts to the dark. In RP, there is an increased absolute rod threshold and dark adaptation is usually prolonged. This test may be useful in detecting early cases.
Visual Field: Kinetic perimetry with Goldmann perimeter characteristically shows a ring scotoma in the mid-periphery of the Visual Field. They usually start as a group of isolated scotomas around 20 degrees from fixation, and gradually coalesce to form a partial followed by a complete ring.
Optical Coherence Tomography (OCT): OCT is a quick, inexpensive, and widely available tool to detect cystic macular lesions, epiretinal membrane, and vitreomacular traction syndrome observed in some RP patients with decreased Central Vision.
Fluorescein Angiography (FA): FA may have a role in documenting the early deterioration of the disease.
Retinitis Pigmentosa: Common Ways of Treatment
Many treatments have been explored without proven benefit for the isolated forms of Retinitis Pigmentosa. These include various vitamins and minerals, vasodilators, tissue therapy with placental extract, cortisone, cervical sympathectomy, injections of a hydrolysate of yeast RNA, ultrasound, transfer factor, dimethyl sulfoxide, ozone, muscle transplants, and subretinal injections of fetal retinal cells. None of the above treatments were conducted in randomized, controlled clinical trials. It is important to note that anecdotal treatment with a subjective improvement of the visual function should be interpreted with caution due to fluctuation in visual acuity and visual fields in this disease. ERG is a better objective measure of remaining retinal function.
Any potential therapy will likely require several years of follow-up to assess efficacy due to the nature of the slow progression of this disease.
Retinitis Pigmentosa: Other treatment considerations
Although light deprivation has not been shown to be of benefit in altering the course of retinal degeneration, it is generally advisable for patients to use ultraviolet and short-wavelength (blue) blocking sunglasses for outdoor activities. Audiology consults should be considered for patients with a possible or known diagnosis of Usher syndrome. Low vision services are designed to benefit those whose ability to function is compromised by visual impairment.
A low vision examination may be useful to help optimize the use of the remaining visual function. Genetic counseling can provide patients and families with information on the inheritance and implications of their genetic disorders and can help them make informed medical and personal decisions.
Retinitis Pigmentosa: Medical follow up
Annual ocular examinations are usually sufficient to measure Visual Acuity and Goldmann visual field. If medical treatment is initiated, more frequent visits and laboratory blood work may be indicated. For example, patients with red blood cell (RBC) docosahexaenoic acid (DHA) level of at least 4% of total RBC fatty acids has been reported to have, on average, a slower rate of decline of visual field sensitivity than those with lower levels. Vitamin A levels and liver function tests should also be done annually if treatment has been initiated.
Retinitis Pigmentosa: Prognosis
Some studies suggest that the rate of progression, the age of onset and the eventual visual loss are related to the mode of inheritance. Autosomal dominant Retinitis Pigmentosa has the best prognosis, with the majority of patients under 30 years having a visual acuity of 20/30 or better. X-linked is the most severe form with appreciable impairment of central visual acuity to 20/200 or less by the fifth decade of life. Autosomal recessive and sporadic cases were intermediate in severity.
Retinitis Pigmentosa and Medical Acupuncture
Recent studies demonstrated acupuncture can elicit activity in specific brain areas in patients with Retinitis Pigmentosa. These specific cerebral activation patterns might explain the therapeutic effects of acupuncture in certain subjects. Regardless of the diagnosis, incurable retinal diseases may respond favorably to Acupuncture. It goes without saying that Acupuncture, as a strictly medical practice, is applied solely by specialized Doctor – Acupuncturists and with specialized acupuncture protocols.
At the “Orasis Acupuncture Institute” there is an Ophthalmologist – Acupuncturist who performs Ophthalmological examinations and practices Medical Acupuncture.