Glaucoma was the cause for blindness in 3.61 million people or 8.4% of the 43.3 million blind people globally in 2020, and glaucoma was the cause for MSVI in 4.14 million people or 1.4% of the 195 million people visually impaired in 2020.6 Our previous publication on vision loss due to glaucoma in 2010 reported lower numbers of affected by blindness (2.1 million) and similar numbers with MSVI (4.2 million).12 In this most recent analysis, glaucoma was ranked as the second leading cause of blindness (after cataract) and fourth leading cause of MSVI, and therefore the most common cause of irreversible blindness, and the second most common cause of irreversible MSVI.6 These figures highlight the importance of glaucoma as a public health concern, and it should be noted that these are almost certainly underestimations due to methodological issues where blindness prevalence surveys (in particular those of rapid design) often assign the most ‘‘treatable” disease as the primary cause of blindness assuming that cataract is more treatable than glaucoma. Furthermore, in advanced glaucoma, individuals may meet WHO perimetric-based definitions of blindness (< 10 degrees of central field in the better eye) whilst retaining normal visual acuity. Hence, as visual field data is rarely collected in population-based surveys, a potentially large but unknown number of individuals are misclassified as visually unimpaired when they may be, in fact, glaucoma blind.
There is increasing global pressure on health-care resources due to the changing demographics of the population. The number of people aged 65 years and older is expected to increase from 700 million to 1.5 billion in the next 30 years, with the largest increases in low- and middle-income countries (LMICs). This will result in populations undergoing “epidemiological transition” and experiencing a higher prevalence of diseases associated with higher development and aging, including glaucoma.3 13 14 The percentage of blindness caused by glaucoma showed regional variations, with relatively low figures in regions with relatively young populations such as South Asia, South-East Asia and Oceania, and Latin America and the Caribbean, and with relatively high figures in regions with relatively old populations such as the high-income regions (Table 1). Bucking this trend were the regions of North Africa and Middle East and Sub-Saharan Africa, both with younger populations than the median global age but with a relatively high contribution of glaucoma to blindness, most probably on account of these regions having the highest age-standardized prevalence of glaucoma-related blindness. Glaucoma causes a particular challenge as many LMICs experience these demographic changes. Due to the typically lengthy asymptomatic phase, it is well documented that in high-income countries, less than half of glaucoma is diagnosed.15, 16 In LMICs, this proportion increases to over 90% and approximately 35% of patients are estimated to be blind at diagnosis.17–20 Furthermore, the higher prevalences on the African continent are almost certainly due to lack of or insufficient access to treatment.
It is encouraging to note that between 2000 and 2020, the global percentage change in age-standardized prevalence of glaucoma-related blindness among adults ≥ 50 years has decreased (-26.06% [95% UI: -26.24, -25.87] among males and females (-21.75% [95% UI: -21.96, -21.54] (Table 4). We identified only two studies that have reported reductions in glaucoma-related blindness incidence, both from high income countries. A recent analysis of the Finnish Register of Vision Impairment and a social insurance register found that the incidence of reported vision impairment in those with treated glaucoma had reduced by a third over 40 years, from 32/100,000 in the 1980s to 21/100,000 in the 2010-19 decade, with no sex differences. This Finnish study reported that the proportion of overall vision impairment had increased in recent decades to approximately 50% suggesting better glaucoma care and earlier diagnosis, and this may be reflected in their finding that age of onset of reported glaucoma-related vision impairment increased in more recent decades.21 The Olmsted County (Minnesota, USA) population-based study reported that the 20-year probability of progression to glaucoma-related blindness in at least one eye had decreased from 26% for subjects diagnosed in 1965–1980 to 13% for those diagnosed in 1981-2000.21 In our analysis, reductions in age-standardized prevalence of glaucoma-related blindness between 2000–2020 in Latin America and Caribbean and Sub-Saharan Africa were not as marked as that for other LMIC regions. These data highlight the urgent need for improved eye health care in these regions, including a sustainable capacity to diagnose and treat glaucoma at earlier stages.
In all regions, in 2020, the age-standardized prevalence of glaucoma-related blindness was higher in males than in females. In Central Asia and high income countries, the age-standardized prevalence of MSVI-related blindness was higher in females than in males, while in other regions there was no sex difference. Male gender has been found to be a significant risk factor for POAG in several studies.4, 23 Women are well documented to be at a higher risk of PACG, the less prevalent but more blinding form of glaucoma.24 The underlying reasons for the different gender-related predispositions are unclear.
Less encouraging than the temporal change in glaucoma blindness, was the finding that between 2000 and 2020, the mean global age-standardized prevalence of glaucoma-related MSVI among adults (≥ 50 years) had increased among males and females (7.3% [95% UI: 7.01, 7.59]) (Table 5). These increases took place mainly in Southeast Asia, East Asia and Oceania, Sub-Saharan Africa, and high-income countries. These data suggest a triaging phenomenon: although efforts to contain glaucoma blindness have had some success, the availability of current resources is not meeting the demands at visually significant but lower thresholds of visual impairment.
The design of our study had potential limitations. First, as we discussed in our report of global prevalence of vision loss, a significant limitation was that many country-years lacked data, or that there was only sub-national data available.5
Second, the majority of population-based studies within the database that reported on vision loss due to glaucoma did not disaggregate their reported findings into glaucoma diagnostic subtypes such as POAG and PACG; therefore, it was not possible to differentiate between glaucoma subtypes in our analysis. Third, as mentioned above, protocol dictated that population-based studies will report one cause as the principal cause for an individual examined in that individual study, so that causal prevalence can be calculated. In situations where multiple disorders contribute equally to visual loss, only the ‘‘most easily preventable” or the ‘‘most readily curable” cause is usually recorded 25 which underestimates the impact of diseases such as glaucoma and diabetic retinopathy. It may hold true in particular for patients with cataract in which the ophthalmoscopical examination of the optic nerve is obscured leading to underdetection of glaucomatous optic nerve damage. Strengths of this study included the large amount of population- based data accessed and utilized and the trend analysis of causes of vision impairment and blindness, usage of non-linear age trends and modelling of data that were not reported by age, systematic quantitative analysis and reporting of uncertainty intervals. The large size of the network of ophthalmic researchers involved in first identification and then evaluation of data sources allowed access to unpublished materials and permitted us to obtain additional unpublished data from study investigators who had only published summary data, to evaluate all the major vision impairment studies, and to include only studies that met specific inclusion criteria regarding population representativeness and clear description and definition of visual acuity procedures.
Given the high prevalence of glaucoma and vision impairment secondary to glaucoma, the economic and social burden
of the condition is substantial. Diagnosed individuals often require lifelong treatment and monitoring. Solutions to these challenges
of diagnosis and ongoing monitoring may arrive through the innovative use of new community care models, availability of home monitoring of both intraocular pressure (IOP) and visual field function, and implementation of screening programs. 26–28 The recently published ‘Package of Eye Care Interventions’ by the World Health Organization provides a useful set of recommended, evidenced-based glaucoma care interventions with material resources required for implementation, health promotion and prevention, screening, diagnosis and monitoring, treatment, and rehabilitation.29 These and other resources are necessary to facilitate policy-makers and technical decision-makers across countries to integrate glaucoma care into the packages and policies of their national health services.