Association between vision impairment and mortality: a systematic review and meta-analysis

Background
The number of individuals with vision impairment worldwide is increasing because of an ageing population. We aimed to systematically identify studies describing the association between vision impairment and mortality, and to assess the association between vision impairment and all-cause mortality.

Methods
For this systematic review and meta-analysis, we searched MEDLINE (Ovid), Embase, and Global Health database on Feb 1, 2020, for studies published in English between database inception and Feb 1, 2020. We included prospective and retrospective cohort studies that measured the association between vision impairment and all-cause mortality in people aged 40 years or older who were followed up for 1 year or more. In a protocol amendment, we also included randomised controlled trials that met the same criteria as for cohort studies, in which the association between visual impairment and mortality was independent of the study intervention. Studies that did not report age-adjusted mortality data, or that focused only on populations with specific health conditions were excluded. Two reviewers independently assessed study eligibility, extracted the data, and assessed risk of bias. We graded the overall certainty of the evidence using the Grading of Recommendations, Assessment, Development and Evaluations framework. We did a random-effects meta-analysis to calculate pooled maximally adjusted hazard ratios (HRs) for all-cause mortality for individuals with a visual acuity of <6/12 versus those with ≥6/12; <6/18 versus those with ≥6/18; <6/60 versus those with ≥6/18; and <6/60 versus those with ≥6/60.

Findings
Our searches identified 3845 articles, of which 28 studies, representing 30 cohorts (446 088 participants) from 12 countries, were included in the systematic review. The meta-analysis included 17 studies, representing 18 cohorts (47 998 participants). There was variability in the methods used to assess and report vision impairment. Pooled HRs for all-cause mortality were 1·29 (95% CI 1·20–1·39) for visual acuity <6/12 versus ≥6/12, with low heterogeneity between studies (n=15; τ2=0·01, I2=31·46%); 1·43 (1·22–1·68) for visual acuity <6/18 versus ≥6/18, with low heterogeneity between studies (n=2; τ2=0·0, I2=0·0%); 1·89 (1·45–2·47) for visual acuity <6/60 versus ≥6/18 (n=1); and 1·02 (0·79–1·32) for visual acuity <6/60 versus ≥6/60 (n=2; τ2=0·02, I2=25·04%). Three studies received an assessment of low risk of bias across all six domains, and six studies had a high risk of bias in one or more domains. Effect sizes were greater for studies that used best-corrected visual acuity compared with those that used presenting visual acuity as the vision assessment method (p=0·0055), but the effect sizes did not vary in terms of risk of bias, study design, or participant-level factors (ie, age). We judged the evidence to be of moderate certainty.

Interpretation
The hazard for all-cause mortality was higher in people with vision impairment compared with those that had normal vision or mild vision impairment, and the magnitude of this effect increased with more severe vision impairment. These findings have implications for promoting healthy longevity and achieving the Sustainable Development Goals.

Funding
Wellcome Trust, Commonwealth Scholarship Commission, National Institutes of Health, Research to Prevent Blindness, the Queen Elizabeth Diamond Jubilee Trust, Moorfields Eye Charity, National Institute for Health Research, Moorfields Biomedical Research Centre, Sightsavers, the Fred Hollows Foundation, the Seva Foundation, the British Council for the Prevention of Blindness, and Christian Blind Mission.

The Lancet Global Health Commission on Global Eye Health: vision beyond 2020

Eye health and vision have widespread and profound implications for many aspects of life, health, sustainable development, and the economy. Yet nowadays, many people, families, and populations continue to suffer the consequences of poor access to high-quality, affordable eye care, leading to vision impairment and blindness.
In 2020, an estimated 596 million people had distance vision impairment worldwide, of whom 43 million were blind. Another 510 million people had uncorrected near vision impairment, simply because of not having reading spectacles. A large proportion of those affected (90%), live in low-income and middle-income countries (LMICs). However, encouragingly, more than 90% of people with vision impairment have a preventable or treatable cause with existing highly cost-effective interventions. Eye conditions affect all stages of life, with young children and older people being particularly affected. Crucially, women, rural populations, and ethnic minority groups are more likely to have vision impairment, and this pervasive inequality needs to be addressed. By 2050, population ageing, growth, and urbanisation might lead to an estimated 895 million people with distance vision impairment, of whom 61 million will be blind. Action to prioritise eye health is needed now.
This Commission defines eye health as maximised vision, ocular health, and functional ability, thereby contributing to overall health and wellbeing, social inclusion, and quality of life. Eye health is essential to achieve many of the Sustainable Development Goals (SDGs). Poor eye health and impaired vision have a negative effect on quality of life and restrict equitable access to and achievement in education and the workplace. Vision loss has substantial financial implications for affected individuals, families, and communities. Although high-quality data for global economic estimates are scarce, particularly for LMICs, conservative assessments based on the latest prevalence figures for 2020 suggest that annual global productivity loss from vision impairment is approximately US$410·7 billion purchasing power parity. Vision impairment reduces mobility, affects mental wellbeing, exacerbates risk of dementia, increases likelihood of falls and road traffic crashes, increases the need for social care, and ultimately leads to higher mortality rates.
By contrast, vision facilitates many daily life activities, enables better educational outcomes, and increases work productivity, reducing inequality. An increasing amount of evidence shows the potential for vision to advance the SDGs, by contributing towards poverty reduction, zero hunger, good health and wellbeing, quality education, gender equality, and decent work. Eye health is a global public priority, transforming lives in both poor and wealthy communities. Therefore, eye health needs to be reframed as a development as well as a health issue and given greater prominence within the global development and health agendas.
Vision loss has many causes that require promotional, preventive, treatment, and rehabilitative interventions. Cataract, uncorrected refractive error, glaucoma, age-related macular degeneration, and diabetic retinopathy are responsible for most global vision impairment. Research has identified treatments to reduce or eliminate blindness from all these conditions; the priority is to deliver treatments where they are most needed. Proven eye care interventions, such as cataract surgery and spectacle provision, are among the most cost-effective in all of health care. Greater financial investment is needed so that millions of people living with unnecessary vision impairment and blindness can benefit from these interventions.
Lessons from the past three decades give hope that this challenge can be met. Between 1990 and 2020, the age-standardised global prevalence of blindness fell by 28·5%. Since the 1990s, prevalence of major infectious causes of blindness—onchocerciasis and trachoma—have declined substantially. Hope remains that by 2030, the transmission of onchocerciasis will be interrupted, and trachoma will be eliminated as a public health problem in every country worldwide. However, the ageing population has led to a higher crude prevalence of age-related causes of blindness, and thus an increased total number of people with blindness in some regions.