Retinitis Pigmentosa (RP) is defined as a hereditary, progressive
             degeneration of the neuroepithelium of the retina characterized by night
             blindness and progressive contraction of the visual field. RP refers to a
             group of hereditary disorders that affect the retina's ability to respond
             to light. It primarily affects rod cells, or the photoreceptors
             responsible for night vision and seeing in dim light. Rod cells also
             account for peripheral vision. Cone cells can also be affected as the
             disease progresses. Cone cells are responsible for color vision and seeing
             RP is a relatively rare condition. It affects an estimated fifty
             thousand to one hundred thousand individuals in the United States.
             Worldwide, RP is estimated to affect 1.5 million people. The incidence of
             Ocular signs start with the breakdown of rod cells. Rods are present
             within the outside macula, or center of the retina. The peripheral retina
             is predominately composed of rod cells. Symptoms of RP usually manifest
             between the ages of 10 and 30. First, night vision decreases along with
             the ability to adjust to dim lighting. When the rod cells and outer cone
             cells are afflicted, the subsequent loss of peripheral sight leads to
             tunnel vision. Rate of progression for RP varies by individual patient and
             There is no treatment for RP. With proper care and diet, the
             progression of the disease can be slowed or halted. Researchers are
             investigating modes of therapy and treatment to possibly reverse the
             degeneration and restore patients' sight.
             How Retinitis Pigmentosa is diagnosed.
             Doctors use a standard array of tests when a patient is displaying
             symptoms of Retinitis Pigmentosa.[iii] These tests are used to determine
             loss of vision and to track the progression of the condition.
             An electroretinagram (ERG) measures the response of the retina to a
             light stimulus. Electrodes are placed be...