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Young and colleagues report that pseudoexfoliation syndrome (PXS) was uncommon in 500 Chinese people aged 60 years and older attending general ophthalmic clinics in Hong Kong with a presumed diagnosis of cataract.1 We have previously carried out a population based assessment of the prevalence of prevalence and risk factors for glaucoma in a district of Singapore, which allowed us to assess the prevalence of PXS in a representative Chinese adult population.2
This study was approved by the ethics review board of Singapore National Eye Centre. All subjects gave written, informed consent. A total of 2000 Chinese Singaporeans aged 40 years and older were identified from the electoral register of Tanjong Pagar district. A total of 283 were considered ineligible (they had died, moved, or were medically unfit to be examined), leaving 1717 potential subjects. From this number 1232 underwent a slit lamp examination before and after pharmacological dilatation of the pupil with phenylephrine (2.5%) and tropicamide (1%). Gonioscopy was carried out before dilatation on all subjects. Pseudoexfoliation material (PXM) on the anterior lens surface and/or pupil margin was specifically sought. Glaucoma was diagnosed on the basis of structural abnormalities of the optic nerve (dimensions of the cup:disc ratio lying outside the 97.5th percentile) combined with a reproducible visual field defect, or advanced structural damage consistent with glaucoma (dimensions of the cup:disc ratio lying outside the 99.5th percentile) if the subject could not complete formal field testing.3
We identified PXM in six eyes of four people (table 1). Two people had definite glaucomatous optic neuropathy, and three had undergone glaucoma surgery. None was using topical or oral medication for glaucoma when seen. The age and sex standardised rate of PXS in Chinese Singaporean adults aged 40 years and older is 0.2% (95% confidence interval; 0.0 to 0.4). In the over 60s, this rose to 0.7% (95% CI: 0.5 to 0.9).
In contrast with the report from Hong Kong, we identified two people in Singapore with PXS and angle closure sufficient to require incisional surgery. Only one person had PXS with glaucoma and open drainage angles.
In previous studies in east Asia, PXM was identified in three of 22 (13.6%) people with glaucomatous optic neuropathy in a Mongolian population. Two of these were classified as open angle glaucoma. The third was blind in both eyes from primary angle closure glaucoma.4 The relative scarcity of PXS in east Asian people contrasts with rates of 6–7.7% in adult black South Africans.5 Similarly, PXS appears relatively common (3.8–6.0%) in south India.6,7 The slightly lower rate among European settlers in Australia aged 49 years and older (2.3%, 95% CI:1.8 to 2.8) is probably genuinely higher than that seen among east Asians.8
In summary, we agree with Young and colleagues that PXS is uncommon in the Chinese cohorts studied to date. However, the tendency for the condition to cluster geographically and in racial subgroups suggests that it may occur with greater frequency in areas not yet studied.
This work was funded by the National Medical Research Council, Singapore.