September 2, 2014

Retinitis Pigmentosa

Abstract

Retinitis pigmentosa (RP) affects approximately 1 in 5000 individuals worldwide. It is a group of hereditary disorders in which there is progressive dysfunction of the retina (the tissue inside the eye that sends images to the brain), more specifically the tissue cells responsible for vision in dim light (rod photoreceptors). The disease is usually inherited (genetically from the parents) although one-third of patients have no other affected relative. It can present in isolation or in association with other findings such as hearing loss, gait disturbance, etc.

The two most common manifestations are night blindness and gradual peripheral visual field (vision on the sides) loss. However, night blindness generally precedes the latter by many years. Symptoms usually present themselves in young adults. The diagnosis is usually confirmed with some tests such as: ERG (evaluates photoreceptor cells function), OCT (picture of the retina), and visual field testing. There is a lot of ongoing research in order to find a possible cure through retinal implants, gene therapy, stem cells, drug therapy. However, currently, our only mean to slow disease progression is with oral intake of vitamin supplements in certain forms of RP.

Susan Wakil

Full article

The retina, the thin layer that lines the back of the eye, is composed of different interconnected cells. These cells serve to convert light into electrical signals that are eventually translated into images by the brain. Among these cells, there are rods (responsible for dark and peripheral vision), cones (responsible for color and fine details vision), and a pigmented cell layer, the retinal pigment epithelium.

A Hereditary Disease

Retinitis pigmentosa (RP) consists of a group of hereditary disease characterized by progressive degeneration and dysfunction of the rods, cones, and pigment epithelial cells resulting in visual disturbances. Its worldwide prevalence is approximately 1 in 5000.

Retinitis pigmentosa is mostly caused by molecular defects in different genes. It is usually inherited (genetically from the parents) and can be passed on by all types of inheritance autosomal dominant (ADRP), autosomal recessive (ARRP), and X-linked (XLRP). Although some people may have no other affected relative.

The term syndromic RP is used when RP is associated with other findings pertaining to the rest of the body (so-called, systemic findings). The most common syndromic form is Usher syndrome, in which RP is found in association with hearing loss. Other common forms include: Bardet-Biedl syndrome (involving obesity, cognitive impairment, polydaxtyly (more than five fingers/toes), hypogenitalism, kidney disease), Kearns-Sayre syndrome (involving cardiac abnormalities), and neuronal ceroid lipofuscinosis (involving neurological problems such as seizures, mental deterioration)

Variable Onsets

The onset and presentation of RP is variable from one person to another. Some may have visual disturbances as early as infancy while others are asymptomatic well into adulthood. Both eyes are usually involved similarly. Typically the rods are the first to be affected therefore people may initially present with defective dark adaptation or night blindness (nyctalopia) followed by progressive loss of peripheral vision (called tunnel vision). As the disease progresses affected people will complain of loss of central vision.

When suspected RP can be diagnosed by an ophthalmologist following examination of the retina. Other tests are also performed to aid in diagnosis. For example, a visual field test (to measure the capacity to see in the periphery (side vision)), an electroretinogram (ERG) (to measure the electrical response of the retina to light stimuli), an optical coherence tomography (OCT) (to take a picture of the retina). Genetic testing is also performed with a blood test.

No Cure, but

Currently there is no cure. Nonetheless, there is a great amount of ongoing research aimed at slowing disease progression and restoring sight. Current studies are evaluating the use of vitamin and antioxidant supplementation. Some specific syndromic forms are being treated with specific dietary modifications and nutritional supplements such as vitamin A, phytanic acid, vitamin E. The use of gene therapy to replace the missing gene is also being investigated in research trials. However, it is not yet possible for all genes. Other therapeutic options being studied are: retinal prostheses (implanted retinal devices that electrically stimulate the retina or your brain), retinal transplantation.

Although it is not a treatment, low-vision support is key in order to manage some manifestations of RP. Numerous devices, such as telescopes, magnifiers, and night vision goggles, are available. These devices are meant to optimize remaining vision thereby improving quality of life. Finally, individuals that are concerned with the risk of transmitting an RP gene to their children are recommended to consult a qualified genetic counselor.

 

Further References:

Canadian Ophthalmology Society: http://www.eyesite.ca/english/public-information/eye-conditions/retinitis-pigmentosa.htm

Emedicine: http://emedicine.medscape.com/article/1227488-overview

Royal National Institute of Blind People: http://www.rnib.org.uk/eyehealth/eyeconditions/eyeconditionsoz/Pages/retinitis_pigmentosa.aspx

The low vision centers from Indiana: http://www.eyeassociates.com/images/understanding_the_visual_problem1.htm