![]() 7 Pigmentation consists of retinal pigment epithelium cells that have detached and migrated to the inner retina after photoreceptor death. Bone spicule pigmentation usually develops in the mid-stages of the disease, starting at the mid-periphery, and moves toward the macula as the disease progresses. The classic triad in RP consists of peripheral bone spicule pigment deposition, blood vessel attenuation (sometimes sclerotic vessels) and optic disc pallor. When working up a patient, the following imaging methods and tests can help clinch the diagnosis of RP: The second most common form of syndromic RP is Bardet Biedl syndrome, an autosomal recessive disorder characterized by obesity, postaxial polydactyly, cognitive impairment, hypogonadotropic hypogonadism, genitourinary defects and renal disease. There are three types of Usher syndrome (I, II, III) with several subtypes, reflecting a combination of clinical and genetic findings. The most common form of syndromic RP is autosomal recessive Usher syndrome, the leading cause of genetic deafness-blindness. Systemic findings often associated with syndromic RP diagnoses are summarized in Table 1. RP can be classified as non-syndromic (affecting only the retina) or syndromic (affecting other tissues and organs). In contrast, EOSRD /SECORD are distinguished by residual, and sometimes improving, visual acuity and function slightly preserved ERG signals and later onset of symptoms, generally around or before the age of 5 years. Electroretinogram signals are either extinguished or severely reduced. Because pigmentary changes may only present later in life, symptoms such as nystagmus, poor object tracking and poor pupillary responses aid in the diagnosis. LCA represents the most severe phenotype, characterized by profound vision impairment at birth or during the first months of life. Although most individuals are diagnosed in early adulthood, 5 a distinct subset of cases falls within the early-onset spectrum of diagnoses, which include Leber congenital amaurosis and early-onset severe retinal dystrophy (EOSRD)/severe early-childhood-onset retinal dystrophy (SECORD). The differential diagnosis for RP can be further refined by age of onset. Classically, X-linked RP patients have an earlier onset and worse prognosis, followed by autosomal recessive patients, with intermediate outcomes and finally, dominant forms have more variable presentations and better prognoses. RP can be inherited in the three major mendelian patterns, but can also present in isolated or simplex cases. 4 Due to the large number of causative genes and known phenotypic variance associated with RP, the disease’s clinical findings, onset and progression may differ considerably between affected individuals. ![]() Less-common clinical findings in patients with RP include cystoid macular edema, macular holes and epiretinal membrane formation. Other findings of RP include posterior subcapsular cataracts (50 percent of cases) 3 and photopsias. Thus, the visual field is progressively reduced in concentric rings, leading to tunnel vision and ultimately, central field loss in end-stage disease. Secondary changes in the retinal cellular milieu due to loss of rod cells eventually result in loss of cone cells. 1 Peripheral vision loss secondary to rod dysfunction occurs early in the disease course, although it may not be recognized by an affected individual. Usually the disease begins with damage and loss of rod cells, leading to nyctalopia and defective dark adaptation, which are the common initial concerns for patients. RP is characterized by progressive vision loss due to abnormalities of the retinal photoreceptor cells or the retinal pigment epithelial cells. Here, we’ll discuss the clinical findings, diagnostic modalities and current clinical trials associated with RP. According to RetNet ( ), a publicly available database of genes and loci mapped to inherited retinal diseases, at least 150 genes have been associated with syndromic and non-syndromic retinitis pigmentosa. Affecting approximately 14,000 individuals worldwide, RP represents one of the leading causes of vision loss, with a broad spectrum of genetic and phenotypic heterogeneity. Inherited retinal diseases, including retinitis pigmentosa, have been the subject of therapeutic clinical trials, including the safe delivery of gene therapy to the subretinal space, with encouraging results.
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