Visual function rather than visual acuity
Authors: Ian Murdoch, David Crabb
Journal: The Lancet Global Health (2021)

We would like to express our gratitude to Matthew Burton and colleagues for the Commission on Global Eye Health (April, 2021),1Burton MJ Ramke J Marques AP et al.The Lancet Global Health Commission on Global Eye Health: vision beyond 2020.Lancet Glob Health. 2021; 9: 489-551Summary Full Text Full Text PDF PubMed Scopus (50) Google Scholar which highlights the magnitude of the challenge. As a plea we would like to mention the glaucomas. We feel this preventable cause of blindness has been insufficiently represented and the burden of this disease group understated because of the use of visual acuity alone to measure disability. Glaucomas result in loss of visual function long before visual acuity is affected, with visual field loss occurring first and central acuity disappearing last. This pattern means that many people will be blind by WHO definitions (visual field loss to less than 10°) but would not have been included in the data described in the Commission if only visual acuity is considered. It is telling to consider why, despite this, glaucoma features as the second leading cause of blindness in the Commission and yet hardly features as a cause of visual impairment (there is no definition of visual impairment by visual field loss). In 2006, Afekhide Omoti and colleagues2Omoti AE Osahon AI Waziri-Erameh MJ Pattern of presentation of primary open-angle glaucoma in Benin City, Nigeria.Trop Doct. 2006; 36: 97-100Crossref PubMed Scopus (38) Google Scholar reported 154 patients in Nigeria with a diagnosis at first presentation of primary open-angle glaucoma. Of 119 patients presenting with subjective visual loss, 38 (25%) were blind when using visual acuity as the measure. A further 87 (57%) were blind when using field loss criteria, increasing the proportion of those blind to 82%. A study3Jones PR Philippin H Makupa WU Burton MJ Crabb DP Severity of visual field loss at first presentation to glaucoma clinics in England and Tanzania.Ophthalmic Epidemiol. 2020; 27: 10-18Crossref PubMed Scopus (4) Google Scholar of visual fields from people newly diagnosed with glaucoma estimated the effect size with greater precision compared with Omoti and colleagues. This underestimate of disease burden is not unique to glaucoma, another example being onchocerciasis.4Murdoch IE Jones BR Cousens S et al.Visual field constriction as a cause of blindness or visual impairment.Bull World Health Organ. 1997; 75: 141-146PubMed Google Scholar Although difficult to quantify, the existence of this additional burden should be recognised. We declare no competing interests. The Lancet Global Health Commission on Global Eye Health: vision beyond 2020Eye 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. Full-Text PDF Open AccessVisual function rather than visual acuity – Authors' replyWe would like to thank Ian Murdoch and David Crabb for their important letter pointing out the tendency to underestimate the global burden of glaucoma when focusing solely on central vision loss. Glaucoma is the leading cause of irreversible vision loss globally, whose share of overall blindness prevalence has been growing steadily as investments have begun to pay off in the fight against diseases such as cataract and trachoma.1,2 Full-Text PDF Open Access