Retinitis Pigmentosa (RP) is an inherited progressive disorder that affects the photoreceptor cells of the retina.  The disease initially causes the loss of rod photoreceptors, leading to night vision loss (nyctalopia) and subsequently peripheral vision loss (tunnel vision).  As the disease progresses, cone photoreceptors are affected, leading to problems with color vision, visual acuity and loss of the central visual field.  Patients may also develop bone spicules in the fundus.  Other symptoms of the disorder include the perception of blinking or shimmering lights (photopsia) and an aversion to bright light (photophobia). 

RP can be diagnosed through fundus examinations, the use of electroretinograms to determine the level of retinal electrical activity and visual field tests to ascertain the loss of peripheral vision.  An important consideration while diagnosing the disorder is whether the patient truly has non-syndromic RP or a larger syndrome such as Bardet-Biedl disease.  This is because the ARL6 gene is responsible for both disorders.  While there are currently no cures for the disorder, vitamin A therapy has been found to help stall disease progression in certain cases.  Patients can also benefit from low vision optical aids and occupational therapy.

The inheritance pattern of this disorder appears to be autosomal recessive.  It is caused by mutations in the ARL6 gene, a GTP binding protein involved in intracellular traffic regulation and protein localization to primary cilium.  While mutations in this gene are usually associated with the more severe Bardet-Biedl syndrome, a homozygous missense mutation (p.A89V) has been found to result in non-syndromic Retinitis Pigmentosa in a Saudi family.