Primary open angle glaucoma (POAG) is the most common form of glaucoma, with at least 80 million people affected globally1. However, the prevalence of POAG varies widely in different parts of the world and between ethnicities1-3, with high rates of POAG in Africa and Latin America, and much lower rates in the Middle East, for example. In contrast, angle closure glaucoma (ACG) is much more common in Asia than elsewhere in the world1-3. The prevalence of glaucoma also increases dramatically with age, particularly from 65 years old. POAG is also more common in males, whereas NTG and ACG are more common in females1.
It has been our clinical impression that there are also differences in glaucoma prevalence between ethnicities within New Zealand. In particular, POAG and normal tension glaucoma (NTG) appear to be uncommon in Māori and Pacific peoples. However, few studies have investigated this further. Interestingly, the only previously published report we could identify was a 1969 New Zealand survey by Mann et al, which demonstrated no glaucoma in the Māori population at the time4. Hence, we decided to conduct a demographic study involving glaucoma patients from Auckland District Health Board (ADHB)5. In this study, Māori made up just 0.5% of all people affected by POAG and Pacific peoples only 0.9% (Table 1). This is despite Māori making up 8% and Pacific peoples 9% of the ADHB catchment population. This suggests that the prevalence of POAG was 16 times less for Māori and 10 times less for Pacific peoples than would have been expected. In contrast, Caucasian (76%) and Indian (10%) ethnicity were over-represented in the study, making up a greater proportion of POAG patients than would be expected.
Table 1. Glaucoma prevalance and ethnicity
Other forms of glaucoma were also uncommon in Māori, with the exception of ACG. In fact, 64% of all glaucoma in Māori was related to ACG, distantly followed by secondary glaucoma (SG) (14%), NTG (14%) and POAG (7%). In Pacific peoples, the majority of glaucoma was either ACG (39%) or SG (39%), with POAG and NTG accounting for 11% each. SG encompassed conditions such as neovascular glaucoma (NVG) and uvetic glaucoma. A high prevalence of NVG secondary to proliferative diabetic retinopathy could be one explanation for the higher rate of secondary glaucoma in Pacific peoples. When looking at the overall glaucoma population, the average age that Māori (60 years) and Pacific peoples (57 years) were affected was also much younger than that of other ethnicities (69 years in the Caucasian group).
Why would Māori and Pasifika have lower rates of glaucoma?
The explanation for the low rates of glaucoma in Māori and Pacific peoples may be related to three factors. The first is population age structure, with Māori and Pacific peoples having a lower life expectancy than other ethnicity groups. According to Statistics New Zealand, 17.1% of the Caucasian population are over 65 years compared with only 5.4% and 4.7% of the Māori and Pacific populations, respectively. Since glaucoma is typically a disease of the elderly, the under-representation of Māori and Pacific peoples may in part be due to their lower life expectancy.
The second factor may be related to healthcare, with studies showing Māori and Pacific peoples have generally poorer access to primary healthcare services6-9. Glaucoma is usually diagnosed through routine screening by optometrists, so lower numbers of Māori and Pacific peoples presenting to optometrists decreases the likelihood of glaucoma being detected. This is particularly relevant for POAG and NTG, which are mostly asymptomatic until more advanced disease has developed.
Fig 1. Glaucoma in Māori and Pasifika
An interesting observation in this study was that Asians were also under-represented in the ACG category (Table 1). We postulated that this could also be due to under-utilisation of primary care services. When the asymptomatic angle closure suspects were removed from the analysis, Asians were in fact over-represented, making up 22.5% of ACG patients.
A third factor could be the presence of genetic factors within Māori and Pacific peoples that protect them from glaucoma. Interestingly, human leukocyte antigen (HLA) loci analysis has demonstrated that Māori and Pacific peoples share a common Mongolian ancestry10. Furthermore, studies from East Asia and Mongolia report a similar disease pattern to Māori and Pacific peoples, with low rates of POAG but higher rates of ACG11-12. This has led to speculation that there may be genes within these ethnicities that protect against POAG and NTG but predispose to them to ACG.
I would like to thank my co-authors from the study, Dr Jeremy Mathan, Professor Dipika Patel and Professor Charles McGhee from Auckland University’s Department of Ophthalmology, and the NZ National Eye Centre, the University of Auckland and the Save Sight Society for funding this research.
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Dr Hussain Patel is a consultant ophthalmologist at Greenlane Clinical Centre specialising in glaucoma and cataract surgery. He is also a senior lecturer in ophthalmology at the University of Auckland and works in private practice at Eye Surgery Associates.