Prevalence of retinitis pigmentosa in Singapore: the Singapore Epidemiology of Eye Diseases Study

Abstract

Retinitis pigmentosa (RP) prevalence data in Asia were limited and mainly reported in previous studies of single ethnicity (Xu et al. 2006; Sen et al. 2008; Sharon & Banin 2015). Herein, we report the prevalence and characteristics of RP observed in a multi-ethnic Asian population from the Singapore Epidemiology of Eye Diseases (SEED) study. The SEED study recruited 10 033 adults aged 40–80 years, comprising of three main ethnic groups in Asia, namely Malay (n = 3380), Indian (n = 3400) and Chinese (n = 3353) (Foong et al. 2007; Lavayan et al. 2009). In this evaluation, 9963 participants who underwent best-corrected visual acuity (BCVA) measurement, retinal examination and photography were included for analysis. Visual impairment (VI) was defined as BCVA with logarithm of minimum of angle of resolution (LogMAR) >0.30. Participants' mean age was 58.9 ± 10.4 years, with 5052 females (50.7%). In the SEED study, six individuals were found to have RP (prevalence 0.06%; 95% CI: 0.02–0.13). By ethnicity, one was Malay, two were Indians, and three were Chinese (prevalence of 0.03%, 0.06% and 0.09%, respectively). Five out of six RP cases were females. All RP cases had bilateral involvement. Of which, six eyes were of early-stage RP, and the remaining eyes were of mid-stage. Notably, none was of late-stage RP. Vision status wise, only three eyes (25%) had VI (BCVA ranging between LogMAR 0.40 and 0.54). The six eyes with early-stage RP had pigmentary changes at the mid-periphery region, modestly attenuated arterioles without bone-spicule deposits (Fig. 1A). The optic disc appeared normal in five eyes and with mild pallor in one eye. The remaining six eyes with mid-stage RP had bone-spicule deposits at the mid-peripheral retina, involving at least two quadrants of retina (Fig. 1B). Attenuated arterioles and optic-disc pallor were observed in these eyes as well. Different degrees of tessellation were observed in all RP eyes, revealing the underlying choroidal vessels. For the three eyes with VI, features such as macular thinning, macular degeneration, cystoid macular oedema, geographical atrophy and retinal dystrophy were observed. Our prevalence rate was similar to previous reports in Arabs, Jews (Sharon & Banin 2015) and Chinese (Xu et al. 2006) (ranging between 0.04% and 0.10%). In comparison, the previous study in South India reported slightly higher prevalence rate (0.17%) (Sen et al. 2008). In our study, we observed females to have higher proportion of RP cases compared to males. This is in contrast with previous studies which reported males having higher prevalence rate than female (Xu et al. 2006; Sharon & Banin 2015). However, it should be noted that the number of cases in this study was few; thus, this conclusion could not be drawn definitively. It should be noted that the clinical diagnosis of RP in this study was based on fundus examination and retinal photography. Electroretinogram, electrooculogram and dark adaptometry which could provide further confirmatory findings were not performed in this study, as these tests were not part of the SEED study’s original protocol. In summary, in a multi-ethnic Asian population, we observed six RP cases for every 10 000 adults aged 40 and above. Among them, the disease severity was generally mild to moderate and still with relatively good BCVA. Our findings from this multi-ethnic Asian population may provide additional insights on RP among Asians. Further evaluation is needed to confirm the ethnic difference in RP observed in our study.