الفهرس 
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Abstract
Retinitis pigmentosa (RP) is a group of inherited disorders characterized by progressive peripheral vision loss and night vision difficulties (nyctalopia) that can lead to central vision loss.
With advances in molecular research, it is now known that RP constitutes many retinal dystrophies and retinal pigment epithelium (RPE) dystrophies caused by molecular defects in more than 40 different genes for isolated RP and more than 50 different genes for syndromic RP. Not only is the genotype heterogeneous, but patients with the same mutation can phenotypically have different disease manifestations.
RP can be passed on by all types of inheritance: approximately 20% of RP is autosomal dominant (ADRP), 20% is autosomal recessive (ARRP), and 10% is X linked (XLRP), while the remaining 50% is found in patients without any known affected relatives. RP is most commonly found in isolation, but it can be associated with systemic disease. The most common systemic association is hearing loss (up to 30% of patients). Many of these patients are diagnosed with Usher syndrome. Other systemic conditions also demonstrate retinal changes identical to RP.
RP is typically thought of as a rod-cone dystrophy in which the genetic defects cause cell death (apoptosis), predominantly in the rod photoreceptors; less commonly, the genetic defects affect the RPE and cone photoreceptors. RP has significant phenotypic variation, as there are many different genes that lead to a diagnosis of RP, and patients with the same genetic mutation can present with very different retinal findings.
Histopathologic changes in RP have been well documented, and, more recently, specific histologic changes associated with certain gene mutations are being reported. The final common pathway remains photoreceptor cell death by apoptosis. The first histologic change found in the photoreceptors is shortening of the rod outer segments. The outer segments progressively shorten, followed by loss of the rod photoreceptor. This occurs most significantly in the mid periphery of the retina. These regions of the retina reflect the cell apoptosis by having decreased nuclei in the outer nuclear
layer. In many cases, the degeneration tends to be worse in the inferior retina, thereby suggesting a role for light exposure.
The final common pathway in RP is typically death of the rod photoreceptors that leads to vision loss. As rods are most densely found in the midperipheral retina, cell loss in this area tends to lead to peripheral vision loss and night vision loss. How a gene mutation leads to slow progressive rod photoreceptor death can occur by many paths, as illustrated by the fact that so many different mutations can lead to a similar clinical picture.
Cone photoreceptor death occurs in a similar manner to rod apoptosis with shortening of the outer segments followed by cell loss. This can occur early or late in the various forms of RP.
• Presenting symptoms of RP vary, but the classic symptoms include the following:
• Nyctalopia: The earliest symptom in RP is most commonly night blindness and is considered a hallmark of the disease.
• Patients may also report a prolonged period of time needed to adapt from light to dark.
• Visual loss: Peripheral vision loss is often asymptomatic; however, some patients notice this vision loss and report it as tunnel vision.
• The loss of vision is painless and slow to progress.
• Photopsia: Many patients with RP report seeing flashes of light (photopsia) and describe them as small, shimmering, blinking lights similar to the symptoms of an ophthalmic migraine. However, in contrast to the patient with an ophthalmic migraine, the photopsia may be continuous rather than episodic.
• A careful family history with pedigree and possible examination of family members can be useful.
• Drug history is essential to rule out phenothiazine/thioridazine toxicity.
The application of molecular biology to clinical medicine is a relatively recent development but has already had great impact upon our understanding.