Prevalence of retinitis pigmentosa in North China: the Beijing Eye Public Health Care Project

Editor, Retinitis pigmentosa has been considered to be one of the common causes of blindness during working life in industrialized countries (Haim 2002). Available population-based studies on the prevalence of retinitis pigmentosa have been conducted mainly in populations in Western countries (Boonstra et al. 2012). For Asia, fewer studies have been performed (Hu 1987; Jonas et al. 2009; Nangia et al. 2012), so that epidemiological data for retinitis pigmentosa in Asia, particularly for mainland China, are limited. Additionally, most population-based studies were usually small or even too small in relation to the low prevalence of retinitis pigmentosa to deliver statistically sound data on the frequency of retinitis pigmentosa. We therefore conducted the present study to investigate the prevalence of retinitis pigmentosa in a large-scaled population-based study in Northern China. The Beijing Eye Public Health Care Project was a population-based study that was designed to screen all inhabitants with an age of 55–85 years and living in the rural regions of the Beijing Municipality (Xu et al. 2012). After training, 2500 ophthalmic technicians went to all houses in the villages, performed an interview and assessed habitual visual acuity. All subjects with an age of 55–85 years and a visual impairment (presenting visual acuity of <0.30 in any eye) were asked to visit the next primary healthcare centre where digitized photographs of the anterior and posterior segment of the eye were taken (non-mydriatic fundus camera; CR DGi, Canon Co. Tokyo, Japan). The photographs were examined in a reading centre. Detailed data on the major causes of visual impairment were available for the inhabitants of randomly selected counties. Of overall 692 323 eligible inhabitants, 562 788 (81.3%) subjects participated. The randomly selected counties with detailed data on the major causes of visual impairment included 279 715 subjects. Visual acuity <0.3 in either eye was detected in 26 241 (9.4%) participants of whom 11 783 (44.9%) subjects had assessable fundus photographs. Retinitis pigmentosa was detected in 32 (0.3%) subjects. Retinitis pigmentosa was bilateral in all patients. In 29 (91%) subjects, visual acuity was lower than 0.30 in both eyes. Prevalence of retinitis pigmentosa was not significantly associated with age (p = 0.12) nor with gender (p = 0.35). Extrapolating the figures to the whole study population, the number of 32 patients with retinitis pigmentosa translated into 71 patients with retinitis pigmentosa related visual impairment out of the whole study population of 279 715 [0.025 ± 0.003%; 95% confidence intervals (CI): 0.02, 0.03] subjects showing a frequency of 1:4000. The prevalence of 1:4000 is only partially comparable with the results of previous smaller scaled investigations with a reported prevalence ranging between 1:4000 and 1.5000 (Haim 2002; Jonas et al. 2009; Boonstra et al. 2012; Nangia et al. 2012). Major limitations of our study have to be taken into account: first, patients with typical retinitis pigmentosa can retain good visual acuity with constricted visual field. In a previous study by Grover et al. (1999), 256 (44.8%) of the 572 patients with retinitis pigmentosa and aged 55+ years had a visual acuity of 20/40 or better. As in our study only subjects with a visual acuity <0.3 underwent fundus photography, the study design will not have identified all patients with retinitis pigmentosa. It led to an underestimation of the prevalence of retinitis pigmentosa. The prevalence of retinitis pigmentosa of about 1:4000 as reported in our study may therefore not have been completely applicable to the prevalence of retinitis pigmentosa in total. Second, although the whole eligible population was primarily screened with a response rate of 81.3%, only those subjects with a visual impairment defined as a presenting visual acuity <0.30 in either eye were further examined. Third, of 26 241 participants with presenting visual acuity <0.3, 11 783 (44.9%) subjects had assessable fundus photographs. The strength of the study was the large study population. In conclusion, retinitis pigmentosa associated with visual impairment was detected in a prevalence of about 1:4000. Calculated for the whole population in China, the figure would be about 325 000 patients with retinitis pigmentosa.