LAUSR

Vision impairment is a significant source of morbidity that affects multiple aspects of systemic well-being, including quality of life, cognition, mental health, and risk of falls, fractures, and other injuries.1 Unilateral vision impairment poses a further challenge, as the loss of binocular vision and stereopsis may further increase the risk of injury and loss of independence.2 While it is known that vision impairment is a global burden, there is currently insufficient information to fully characterize this burden. Recent reports by the US National Academy of Medicine1 and the World Health Organization3 have highlighted the difficulties of estimating the prevalence and causes of vision impairment on a national and international level, largely due to the lack of availability of population-based studies. Furthermore, most available studies do not differentiate between unilateral and bilateral vision impairment, despite the important differences in functioning that occur between these 2 types. Foreman et al4 performed a population-based study that addresses several of the important issues outlined above. The authors studied participants of the National Eye Health Survey in Australia, which is a nationwide survey that systematically samples indigenous Australians 40 years and older and nonindigenous Australians 50 years and older. In this study, 1738 indigenous Australians and 3098 nonindigenous Australians underwent distance visual acuity testing; unilateral vision impairment was defined as presenting a visual acuity of less than 6/12 in 1 eye and more than 6/12 in the other eye, and unilateral blindness was defined as presenting a visual acuity of less than 6/60 in 1 eye and more than 6/12 in the other eye. Participants who were identified as having unilateral vision impairment or blindness underwent anterior and posterior segment photography and intraocular pressure testing, and those whose vision impairment improved with pinhole also underwent autorefraction. Trained study staff members assessed photographs and clinical examination results to determine the cause of vision impairment. The authors determined that the weighted prevalences of unilateral vision impairment and blindness were 12.5% and 2.4%, respectively, among indigenous Australians and 14.6% and 1.4%, respectively, among nonindigenous Australians. In both groups, the leading causes of unilateral vision impairment were uncorrected refractive error and cataracts, at a prevalence of 70% to 75%. The leading causes of blindness were corneal pathology and cataracts in indigenous Australians and amblyopia and trauma in nonindigenous Australians. An important conclusion of the study was that most cases of unilateral vision loss in Australia are reversible. The work by Foreman et al4 is significant for several reasons. Most notably, their focus on unilateral vision impairment identifies a problem within health care that is unique to eye care clinicians. Studies have suggested that patients with unilateral vision impairment have similar difficulty with falling and independence as patients with bilateral vision impairment.2 Furthermore, studies have reported that patients who undergo cataract surgery in both eyes report improved functioning compared with patients who only undergo surgery in 1 eye.5,6 The finding of Foreman et al4 of the prevalence of unilateral vision impairment among the National Eye Health Survey population suggests that a significant proportion of vision impairment in Australia may be due to unilateral causes. More importantly, their discovery that most cases of unilateral vision impairment are reversible suggests that a significant proportion of vision impairment in Australia may be eliminated by addressing these cases, which is an important step toward reducing the burden of vision impairment in Australia. Another important aspect of the Foreman et al study4 is the differentiation between indigenous and nonindigenous populations. A major limitation of the largescale surveillance of eye disease is the exclusion of populations who are uninsured or underserved.1 Including the indigenous population identifies causes of vision impairment that are unique to this underserved population and highlights the importance of surveying underserved and uninsured populations before creating new health policy initiatives. Finally, Foreman et al4 are to be commended on their use of a nationwide database with systematic sampling to characterize the prevalence and etiology of unilateral vision impairment on a national level. There are several questions for future investigation that stem from the work of Foreman et al.4 As the authors indicate, amblyopia and trauma were 2 common causes of unilateral vision loss that were identified in their study, and to our knowledge, these diseases are infrequently studied in population-based research. Future population-based studies of the prevalence and outcomes of these entities would be informative for large-scale eye health initiatives. Additionally, as mentioned previously, addressing reversible causes of unilateral vision impairment holds the potential to eliminate cases of vision impairment and reduce the global burden of vision impairment; studies with interventions to address reversible unilateral vision impairment would be informative regarding the feasibility and planning for population-based interventions. Finally, data on long-term outcomes and morbidity rates in individuals with unilateral vision impairment are limited, and additional studies of outcomes in this population are warranted to further understand the morbidity rates that are associated with unilateral vision impairment. Related article Reducing the Burden of Unilateral Vision Impairment in Australia Invited Commentary