Prevalence of retinitis pigmentosa in India: the Central India Eye and Medical Study

Editor, Retinitis pigmentosa is considered to be one of the frequent causes of blindness during working life in industrialized countries (Haim 2002). Knowledge of the prevalence of retinitis pigmentosa is, therefore, important. Available population-based studies on the prevalence of retinitis pigmentosa have been conducted mainly in populations in the Western countries (Bundey & Crews 1984; Bunker et al. 1984). For Asia, only few studies have addressed the issue (Hu 1987; Xu et al.2006), and there is no specific information about India with the world′s second largest population. It was, therefore, the purpose of this study to investigate the prevalence of retinitis pigmentosa in India in a population-based study design. The Central India Eye and Medical Study is a population-based cross-sectional study performed in rural Central India (Nangia et al. 2008, 2012). The Medical Ethics Committee of the Medical Faculty Mannheim of the Ruprecht-Karls-University Heidelberg approved the study, and all participants gave informed consent. Inclusion criterion was an age of 30+ years. Of 5885 subjects, 4711 (80.1%) people participated. The ophthalmic evaluation included refraction, biometry and photography of the lens, optic disc and macula. Diagnostic criteria for retinitis pigmentosa were visual field defects on frequency doubling perimetry, typical ophthalmoscopic abnormalities and no other reason for perimetric defects and fundus abnormalities. Statistical analysis was performed using the spss software (version 19.0.; IBM-SPSS, Chicago, IL, USA). Assessable fundus photographs were available for 4543 (96.4%) participants. Mean age was 48.8 ± 13.0 years, and mean refractive error was −0.10 ± 1.72 dioptres. Retinitis pigmentosa was detected in six subjects (prevalence: 0.13 ± 0.5%) (mean ± standard error) [95% confidence interval (CI): 0.03, 0.2] (four men) with a mean age of 49.3 ± 17.2 years (range: 31–70 years). Visual acuity ranged between 20/20 (age: 35 and 50 years) and no light perception (70-years old patient). The subjects with retinitis pigmentosa as compared with the remaining study population did not vary significantly in age (p = 0.94), gender (p = 0.43), level of education (p = 0.53), systolic (p = 0.12) and diastolic (p = 0.41) blood pressure, prevalence of arterial hypertension (p = 0.61) and diabetes mellitus (p = 1.0), blood concentration of glucose (p = 0.27), cholesterol (p = 0.69), high-density lipoproteins (p = 0.37) and creatinine (p = 0.62), refractive error (p = 0.11), anterior chamber depth (p = 0.94), lens thickness (p = 0.46), axial length (p = 0.62) and intraocular pressure (p = 0.99). Central corneal thickness was significantly (p = 0.01) lower in the retinitis pigmentosa group than in the group of the remaining study participants [474 ± 21 μm (median: 475 μm; range: 437–501 μm) versus 514 ± 33 μm (median: 518 μm; range: 290–666 μm)]. Using visual field criteria and the ophthalmoscopic fundus appearance, prevalence of retinitis pigmentosa was about 1:750 in the adult population of rural Central India. This figure is slightly lower or similar to the figure reported by Sen et al. (2008) from the South Indian population with a prevalence of 13/7461 or 0.17%. If that study was stratified into the urban part (prevalence: 1/930 or 0.11%) and the rural part (prevalence: 1/372 or 0.27%), the prevalence for retinitis pigmentosa in the rural region was considerably higher than in our study on the rural Central Indian population. These figures from India are higher than data from early surveys from other countries such as the study conducted by Bunker et al. (1984) in Maine/USA in 1984 (prevalence rate:1:4756) or performed by Bundey and Crews (1984) in Birmingham, England (prevalence rate: 1:4869). In Shanghai, China, Hu recorded a prevalence of 1:3784 (Hu 1987). A nation-wide registration of Danish patients with retinitis pigmentosa revealed a prevalence of 1:3943 (Haim 2002). The figures of our study agree well with the data from the Beijing Eye Study, in which the prevalence of retinitis pigmentosa was about 1:1000 (Xu et al. 2006). The reason for the relatively high rate of retinitis pigmentosa in the Indian population, in particular for the rural regions, may be the relatively high rate of consanguinity (Nirmalan et al. 2006). Calculated for the whole population of India (389 million subjects aged 30+ years), our result will transfer into a figure of approximately half a million Indians with retinitis pigmentosa or about 1.4 million Indians carrying the genes for retinitis pigmentosa. Interestingly, the study group with retinitis pigmentosa had relatively low central corneal thickness measurements. Limitations of our study are that the number of subjects with retinitis pigmentosa was too low for a detailed statistical analysis and that as in any population-based study so far, the diagnosis of retinitis pigmentosa was not confirmed by electrophysiological testing. In conclusion, retinitis pigmentosa occurred in 1 of 750 subjects aged 30+ years in rural Central India.