New research published in Eye sought to estimate the number of individuals globally with blindness or visual impairment due to glaucoma between 2000 and 2020.
Give me some background first.
While there are a number of treatment options available, glaucoma is the most common cause of irreversible blindness worldwide.
The American Academy of Ophthalmology estimates that by 2040, the number of people with glaucoma worldwide will increase to 111.8 million. Despite this, there is a lack of awareness regarding glaucoma and at least half of individuals affected by glaucoma are unaware they have it.
Now, talk about the study.
This study was a systematic review and meta-analysis of previously published population studies and grey literature (information created outside of traditional publishing and distribution channels) from 2000 to 2020 to estimate global and regional trends in the number of individuals with vision loss due to glaucoma.
This data was collected from within the Global Vision Database, curated by the Vision Loss Expert Group (VLEG), which is an international group comprised mainly of ophthalmologists and optometrists with experience in ophthalmic epidemiology.
Researchers separated raw data into the following categories:
- All-cause moderate vision loss
- Severe vision loss
- Blindness
And the number of studies identified?
In total, 137 studies were identified; of that, data was extracted from 70 studies (in a 2010 review) and an additional 67 studies (in a 2014-2018 review).
Note: These studies were largely national and subnational cross-sectional surveys.
How was vision loss defined?
The researchers defined the levels of vision loss for their analysis using the International Classification of Diseases 11th edition criteria for vision loss:
- Moderate to severe vision loss (MSVI)
- Visual activity (VA) of 6/60 or better but <6/18 (moderate)
- VA of 3/60 or better but <6/60 (severe vision loss)
- Blindness
- Presenting VA <3/60
The data was then input into a mixed-effects meta-regression tool developed by the Institute for Health Metrics and Evaluation (IHME).
How was information extracted?
First: Presenting vision impairment was the reference definition for each severity level.
Researchers then extracted undercorrected refractive error data directly from data sources when possible.
However, if the study reported data for a given location, year, sex, and age group, they calculated by subtracting best-corrected vision impairment from presenting vision impairment prevalence for each severity level.
What were some of the model causes for visual impairment and blindness?
- Cataracts (20 age year minimum for inclusion of data)
- Diabetic retinopathy (20 age year minimum for inclusion of data)
- Age-related macular degeneration (45 age year minimum for inclusion of data)
- Glaucoma (45 age year minimum for inclusion of data)
- Undercorrected refractive error
- Myopic macular degeneration
- Other causes of vision impairment (in aggregate)
A residual category was created by combining other vision impairments with less prevalent causes of vision impairment such as retinopathy of prematurity (ROP) and vitamin A deficiency.
What about other factors? Location, age, and sex estimates of MSVI and blindness were created using Disease Modelling Meta-Regression (Dismod-MR) 2.1. The estimates were then age-standardized using the Global Vision Database (GBD) standard population.
Now these findings.
Overall, the researchers found that a total of 3.61 million people in 2020 were blind, with almost 4.14 million visually impaired by glaucoma.
Further, glaucoma caused 8.39% (95% uncertainty intervals [UIs]: 6.54, 10.29) of all blindness and 1.41% (95% UI: 1.10, 1.75) of all MSVI worldwide in 2020.
Give me more details.
The researchers also found the highest proportion of blindness due to glaucoma was in high-income countries (the investigators did not provide specific names for these countries) (26.12% [95% UI: 20.72, 32.09]).
They further estimated that:
- 2 million males of all ages had glaucoma-related MSVI
- 2.14 million females of all ages had glaucoma-related MSVI
- 1.89 million males of all ages were blind due to glaucoma
- 1.72 million females of all ages were blind due to glaucoma
- 1.89 million males aged 50+ were blind due to glaucoma
- 1.71 million females aged 50+ were blind due to glaucoma
Tell me more.
The researchers reported that between 2000 and 2020 the global percentage change in age-standardized prevalence of glaucoma-related blindness among adults aged 50+ decreased as follows:
- -26.06% (95% UI: -26.24, -25.870 among males
- -21.75% (95% UI: -21.96, -21.54) among females
They also found that between 2000 and 2022, the average global age-standardized prevalence of glaucoma-related MSVI among adults aged 50+ increased by:
- 3.70% (95% UI: 3.42, 3.98) among males
- 7.30% (95% UI: 7.01, 7.59) among females
What were the demographics of these increases?
These increases primarily took place in Southeast Asia, East Asia and Oceania, Sub-Saharan Africa, and high-income countries.
Note: All regions in 2020 demonstrated the age-standardized prevalence of glaucoma-related blindness was higher in males than in females.
Limitations?
For starters, the researchers noted that a number of countries either lacked data or only provided sub-national data available for the period analyzed.
They also stated that a majority of the population-based studies analyzed that reported on glaucoma due to vision loss did not separate their findings into glaucoma diagnostic subtypes—example: primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG)—which meant the researchers could not differentiate between glaucoma types in their analysis.
Expert opinion?
In this analysis, the researchers reported that glaucoma was ranked as the second-leading cause of blindness and fourth-leading cause of MSVI.
Thus: The disease is the overall most common cause of irreversible blindness and the second-leading cause of irreversible MSVI.
Anything else?
The researchers emphasized that early detection of improved awareness of glaucoma is imperative.
They also highlighted an article published by the World Health Care Organization that they stated, “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.”
What else?
Lastly, the population-based studies reported only one principal cause of individuals examined in their analysis, meaning if multiple disorders were equally contributing to the individual’s vision loss, only the most “easily preventable” or “readily curable” cause would be recorded.
The researchers stated that this would underestimate the impact of diseases such as glaucoma and diabetic retinopathy.
Take home.
While glaucoma-linked blindness has declined since 2000, glaucoma remains a major cause of blindness around the globe.