Prevalence and Causes of Unilateral Vision Impairment and Unilateral Blindness in Australia: The National Eye Health Survey

Key Points

Question  What are the prevalence and major causes of unilateral vision impairment and unilateral blindness in Australia?

Findings  This population-based survey included 1738 indigenous Australians and 3098 nonindigenous Australians and found that the age-adjusted and sex-adjusted prevalence of unilateral vision impairment and unilateral blindness were higher in indigenous Australians than in nonindigenous Australians (18.7% and 2.9% vs 14.5% and 1.3%). Uncorrected refractive errors and cataracts were leading causes of unilateral vision impairment in both populations (70%-75%).

Meaning  While unilateral vision impairment and unilateral blindness are highly prevalent in Australia, most cases are avoidable, and health care interventions that address unilateral vision loss are therefore warranted.

Importance  This study determines the prevalence of unilateral vision impairment (VI) and unilateral blindness to assist in policy formulation for eye health care services.

Objective  To determine the prevalence and causes of unilateral VI and unilateral blindness in Australia.

Design, Setting, and Participants  This cross-sectional population-based survey was conducted from March 2015 to April 2016 at 30 randomly selected sites across all strata of geographic remoteness in Australia. A total of 1738 indigenous Australians 40 years or older and 3098 nonindigenous Australians 50 years or older were included.

Main Outcomes and Measures  The prevalence and causes of unilateral vision impairment and blindness, defined as presenting visual acuity worse than 6/12 and 6/60, respectively, in the worse eye, and 6/12 or better in the better eye.

Results  Of the 1738 indigenous Australians, mean (SD) age was 55.0 (10.0) years, and 1024 participants (58.9%) were female. Among the 3098 nonindigenous Australians, mean (SD) age was 66.6 (9.7) years, and 1661 participants (53.6%) were female. The weighted prevalence of unilateral VI in indigenous Australians was 12.5% (95% CI, 11.0%-14.2%) and the prevalence of unilateral blindness was 2.4% (95% CI, 1.7%-3.3%), respectively. In nonindigenous Australians, the prevalence of unilateral VI was 14.6% (95% CI, 13.1%-16.3%) and unilateral blindness was found in 1.4% (95% CI, 1.0%-1.8%). The age-adjusted and sex-adjusted prevalence of unilateral vision loss was higher in indigenous Australians than nonindigenous Australians (VI: 18.7% vs 14.5%; P = .02; blindness: 2.9% vs 1.3%; P = .02). Risk factors for unilateral vision loss included older age (odds ratio [OR], 1.60 for each decade of age for indigenous Australians; 95% CI, 1.39-1.86; OR, 1.65 per decade for nonindigenous Australians; 95% CI, 1.38-1.96), very remote residence (OR, 1.65; 95% CI, 1.01-2.74) and self-reported diabetes (OR, 1.52; 95% CI, 1.12-2.07) for indigenous Australians, and having not undergone an eye examination in the past 2 years for nonindigenous Australians (OR, 1.54; 95% CI, 1.04-2.27). Uncorrected refractive error and cataract were leading causes of unilateral VI in both populations (70%-75%). Corneal pathology (16.7%) and cataract (13.9%) were leading causes of unilateral blindness in indigenous Australians, while amblyopia (18.8%), trauma (16.7%), and age-related macular degeneration (10.4%) were major causes of unilateral blindness in nonindigenous Australians.

Conclusions and Relevance  Unilateral vision loss is prevalent in indigenous and nonindigenous Australians; however, most cases are avoidable. As those with unilateral vision loss caused by cataract and posterior segment diseases may be at great risk of progressing to bilateral blindness, national blindness prevention programs may benefit from prioritizing examination and treatment of those with unilateral vision loss.

The profound impact of bilateral vision impairment (VI) and blindness on quality of life, functionality, and mortality has been well characterized.^1,2 Despite the comparatively smaller body of literature on unilateral vision loss, there is evidence that, despite having a functional fellow eye, those with unilateral vision loss may be greatly affected in several domains. Loss of stereoscopic binocular vision and the reduction in visual fields result in reduced visual-motor coordination, depth perception, and spatial orientation.³ Consequently, people with unilateral vision loss are more likely to have motor vehicle crashes;⁴ they also have a greater propensity for falling, are more dependent on others, and have poorer physical and mental health than the general population.⁵

Most surveys on VI and blindness report the prevalence of bilateral vision loss and neglect unilateral vision loss.^6-9 Systematic reviews, including those by the Global Burden of Disease Vision Loss Expert Group^10,11 and the World Health Organization,¹² have provided comprehensive global epidemiological data on bilateral vision loss, but not unilateral vision loss. The limited number of surveys that have investigated unilateral vision loss have consistently demonstrated that it is more prevalent than bilateral vision loss, ranging from 1.8 times higher in Cape Verde Islands¹³ to about 4 times higher in Vanuatu¹⁴ and Iceland.¹⁵ This highlights the need for interventions to reduce the burden of unilateral vision loss.

In Australia, there is a paucity of population-based data on unilateral vision loss. Current prevalence estimates for the general population are derived from subnational surveys conducted in the 1990s. These surveys included 1 in Victoria that did not report causes of vision loss,⁵ 1 in New South Wales that reported prevalence based on best-corrected visual acuity (BCVA) rather than on presenting visual acuity (PVA)^16,17 and 1 in South Australia¹⁸ that provided the prevalence of unilateral blindness but not VI. Nonetheless, these surveys indicated that unilateral VI and unilateral blindness are prevalent in older Australians, affecting up to 11.6%⁵ and 3.7%¹⁸ of the population, respectively.

The 2008 National Indigenous Eye Health Survey reported a prevalence of unilateral VI and blindness of 12.8% and 2.7%,¹⁹ respectively, while the Central Australian Ocular Health Study (conducted from 2005 through 2008) reported the prevalence of unilateral blindness (5.2%)²⁰ in the Australian indigenous population. Changes in population parameters since the completion of these studies may affect the epidemiology of unilateral vision loss, such as population aging²¹ and the increasing incidence of diabetes,²² and this necessitates further investigation.

The National Eye Health Survey (NEHS), conducted between March 2015 and April 2016, collected ophthalmological data from a nationally representative sample of indigenous and nonindigenous Australian adults. This article reports the prevalence, causes, and risk factors of unilateral VI and unilateral blindness in indigenous and nonindigenous participants.

Participants were selected using multistage random-cluster sampling, as described previously.²³ Population clusters containing a nationally representative sample of indigenous Australians 40 years or older and nonindigenous Australians 50 years or older were identified from 2011 census data. A younger age was selected for indigenous participants to reflect the earlier onset of diseases, such as diabetes, in this population.²⁴ In the first stage of sampling, a pool of 2097 geographic areas defined by the Australian Bureau of Statistics as statistical areas level 2²⁵ were stratified by remoteness (major city, inner regional, outer regional, remote, and very remote), and a total of 30 clusters were selected. A smaller area (statistic area level 1) from within each statistical area level 2 was selected for participant recruitment.

Recruiters used a systematic door-to-door approach (described elsewhere²⁶) to engage residents. To ensure that indigenous participants were recruited in a culturally appropriate manner, recruiters collaborated with indigenous community members to contact residents through several methods, including door-to-door, telephone, word-of-mouth, and concurrent medical clinics. Recruiters contacted 11 883 residents, of whom 6760 (56.9%) were eligible to participate. Indigenous Australians younger than 40 years, nonindigenous Australians younger than 50 years, and those who did not reside at the residence at the time of recruitment were ineligible.

Ethical approval was obtained from Royal Victorian Eye and Ear Hospital Human Research Ethics Committee and state-based indigenous ethical bodies. This study was conducted in accordance with the tenets of the Declaration of Helsinki as revised in 2013. All participants provided written informed consent.

Trained examiners including optometrists, an ophthalmologist, orthoptists, and closely supervised research assistants used a standardised questionnaire to collect data on participants’ sociodemographic characteristics, ocular histories, and stroke and diabetes histories. Examiners conducted a standardised eye examination, described in detail elsewhere.²⁶ Presenting visual acuity was assessed in each eye separately using a logMAR chart (Brien Holden Vision Institute, Australia). Unilateral VI and unilateral blindness were defined as PVA of less than 6/12 and 6/60, respectively, in the worse eye, and 6/12 or greater in the better eye. Pinhole testing was conducted on eyes with PVA of less than 6/12. If visual acuity improved to equal to or greater than 6/12, handheld autorefraction was performed using a Nidek ARK-30 Type-R handheld auto-refractor/keratometer (Nidek Co. Ltd). Best corrected visual acuity was then measured.

The anterior segment was examined using a handheld slit lamp (Keeler Ophthalmic Instruments). If PVA was less than 6/12 in either eye, anterior segment photographs were taken of the affected eye or eyes using the manual anterior segment photography function on a nonmydriatic Digital Retinography System camera (CenterVue, SpA). This camera was also used to take 2-field, 45° color fundus photographs of each retina, centered on the macula and optic disc. Mydriasis was induced with tropicamide, 0.5%, if physiological mydriasis was insufficient to obtain high-quality photographs. Mydriasis was avoided if anterior chamber angles were deemed too narrow (grades 1 or 2 by the Van Herick method) because of the risk of acute angle closure. For these participants, nondilated photography was reattempted and retinal graders at the Centre for Eye Research Australia used the best quality photographs to identify pathology where possible. Intraocular pressure was measured using a tonometer (iCare, Finland). Examiners provided participants with verbal feedback on their results, a certificate of participation, and free sunglasses.

Trained retinal graders graded the retinal images using OpenClinica software (OpenClinica LLC) according to validated standard protocols.^27-29 Cataracts were categorized by 2 independent graders based on anterior segment and fundus photographs into 1 of 3 groups: no cataract, probable cataract, or definite cataract. Graders achieved high interrater reliability (85%) and intrarater reliability (94% and 96% for the 2 graders). Any disagreements were adjudicated by a third independent grader. In cases where photographs were unavailable, a cataract grade was assigned based on the anterior segment examination by a trained examiner. Participants deemed to have probable or definite cataracts were considered to have cataracts for the purposes of this study. The condition causing the greatest limitation to vision based on retinal photographs, grading data, and examination results was assigned the main cause of unilateral vision loss. Uncorrected refractive error was assigned as the main cause of unilateral VI if BCVA was 6/12 or greater in the affected eye. For cases in which more than 1 condition was present and none could be discerned as the main cause, VI or blindness were attributed to multiple mechanisms. The cause of VI was considered “not determinable” if no main cause could be identified.

The prevalence of unilateral VI and unilateral blindness was weighted based on stratified sampling methods. Because sampling was stratified by indigeneity, the prevalence in indigenous and nonindigenous Australians were derived separately. Weighted proportions were age-adjusted and sex-adjusted to facilitate χ² comparisons between indigenous and nonindigenous groups. Univariable and multivariable logistic regression was used to identify risk factors for unilateral vision loss. To provide adequate statistical power in logistic regression analysis, participants with unilateral VI and unilateral blindness (ie, all participants with PVA of less than 6/12 in the worse eye and PVA equal to or greater than 6/12 in the better eye) were combined into 1 group named unilateral vision loss. Tabulated data including disaggregated prevalence estimates and risk factors are presented for the combined unilateral vision loss group. All data were analyzed using Stata software version 14.2.0 (StataCorp). P values of .05 or less were considered to be statistically significant.

The study sample consisted of 1738 indigenous Australians with a mean (SD) age of 55.0 (10.0) years (range, 40 to 92 years); 714, or 41.1%, were male. An additional 3098 nonindigenous Australians with a mean (SD) age of 66.6 (9.7) years (range, 50-98 years), participated; of these, 1437 (46.4%) were male. A response rate of 71.5% was achieved.

In total, 214 of 1738 indigenous Australians had unilateral VI, with a weighted prevalence of 12.5% (95% CI, 11.0%-14.2%). This corresponds to 16 739 indigenous Australians in the national population. The weighted prevalence of unilateral blindness was 2.4% (95% CI, 1.7%-3.3%) in indigenous Australians (36 of 1738 participants), equivalent to 3188 people in Australia’s national indigenous population. In nonindigenous Australians, the weighted prevalence estimates of unilateral VI and unilateral blindness were 14.9% (95% CI, 13.1%-16.8%; 453 of 3098 participants) and 1.4% (95% CI, 1.0%-1.8%; 48 of 3098), respectively, corresponding to an estimated 866 291 and 80 214 nonindigenous Australians in the national population.

The age-adjusted and sex-adjusted prevalence of unilateral VI in indigenous Australians was 18.7% (95% CI, 15.7-21.8), which was significantly higher than in the nonindigenous group, which had an adjusted prevalence of 14.5% (95% CI, 12.8%-16.2%; P = .02). Similarly, the adjusted prevalence of unilateral blindness was higher in indigenous Australians (2.9%; 95% CI, 1.4%-4.5%) than in their nonindigenous counterparts (1.3%; 95% CI, 1.0%-1.7%, P = .02).

The prevalence of unilateral vision loss more than quadrupled from 8.0% in indigenous Australians aged 40 to 49 years to 34.3% in those aged 70 to 79 years (Table 1). This increase was significant in multivariable logistic regression (odds ratio [OR], 1.60/decade; 95% CI, 1.39-1.86) (Table 2). Older age increased the odds of unilateral vision loss in nonindigenous Australians (OR, 1.65/decade; 95% CI, 1.38-1.96), with a tripling of the prevalence from 8.1% in those aged 50 to 59 years to 27.2% in those aged 80 to 89 years. Very remote residence was also a risk factor for unilateral vision loss in indigenous Australians (OR, 1.65; 95% CI, 1.01-2.74), as was self-reported diabetes (OR, 1.52; 95% CI, 1.12-2.07). For nonindigenous Australians, having not undergone an eye examination within the past 2 years was a significant risk factor (OR, 1.54; 95% CI, 1.04-2.27).

Uncorrected refractive error was the leading cause of unilateral VI in both indigenous Australians (n = 138/214; 64.5%) and nonindigenous Australians (n = 257/453; 56.7%) (Table 3). Cataract was the second leading cause in both groups; it was present in 23/214, or 10.7%, of indigenous Australians with VI and 62/453, or 13.7%, of nonindigenous Australians with VI. Diabetic retinopathy (DR) was responsible for 4.2% of unilateral VI in indigenous Australians (n = 9/214), and age-related macular degeneration (AMD) caused 5.7% of unilateral VI in nonindigenous Australians (n = 26/453). More than 6% of nonindigenous Australians (n = 29/453) and more than 3% of indigenous Australians (n = 7/214) had unilateral VI due to amblyopia.

The combined group of other retinal conditions, including macular scarring, macular holes, epiretinal membranes, and retinal detachment, caused almost one-fifth of unilateral blindness in indigenous Australians. Corneal pathology (n = 6/36; 16.7%), cataract (n = 5/36; 13.9%), DR (n = 3/36; 8.3%), ocular trauma (n = 3/36; 8.3%), and enucleation (n = 3/36; 8.3%) all contributed substantially to the burden of unilateral blindness in this group. In nonindigenous Australians, amblyopia was the leading cause of unilateral blindness (n = 9/48; 18.8%), followed by trauma (n = 4/48; 8.3%), cataract (n = 5/48; 10.4%), and AMD (n = 5/48; 10.4%).

The age-specific contribution of uncorrected refractive error to unilateral vision loss remained stable from the indigenous Australian subgroups aged 40 to 49 years to 70 to 79 years, and from the nonindigenous Australian subgroups aged 50 to 59 years to 70 to 79 years, after which this proportion decreased as the age-specific attribution of other diseases increased (Table 4). The proportion of vision loss in indigenous Australians due to cataract increased 5-fold from 40 to 49 years (n = 2/47; 4.3%) to 70 to 79 years (n = 8/41; 19.5%) and then increased sharply to 60% in those 80 years or older (n = 3/5). Similarly, DR was responsible for 5 times as many cases of unilateral vision loss in those aged 60 to 69 years than those aged 40 to 49 years. The increase in AMD as a cause of unilateral vision loss in nonindigenous Australians from 1.5% (n = 1/68; 95% CI, 0.04%-7.9%) in the subgroup aged 50 to 59 years to 28.6% (n = 2/7; 95% CI, 3.7%-71.0%) in those older than 90 years (a 19-fold increase) was the largest relative age-related increase for any condition.

We have demonstrated that a substantial proportion of both indigenous and nonindigenous Australians are unilaterally vision-impaired or blind, with almost 20 000 indigenous Australians and 1 million nonindigenous Australians affected. These findings, in conjunction with the main causes of unilateral vision loss and epidemiological risk factors identified in this article, will inform comprehensive eye health care programs that include targeted interventions for unilateral vision loss.

The age-adjusted and sex-adjusted prevalence of both unilateral VI and unilateral blindness were higher in indigenous Australians than their nonindigenous counterparts. Although the gap in indigenous eye health has been well-documented,^30-32 this is the first time, to our knowledge, that the gap in unilateral vision loss between indigenous and nonindigenous Australians has been quantified.

Despite efforts to improve indigenous eye health in recent years,^33,34 data from 2008^19,30 suggest that the prevalence of both unilateral VI and unilateral blindness remained unchanged since that point (unilateral VI, 12.5% in 2015 vs 12.8% in 2008; unilateral blindness, 2.4% in 2015 vs 2.7% in 2008). Refractive error and cataract continue to be the leading causes of unilateral VI in this group. These reversible conditions potentially provide a cost-effective target for three-quarters of unilateral vision loss.^35,36 Those with cataract-related unilateral vision loss may be at risk of having a less-developed cataract in the fellow eye that has not yet become sufficiently dense to impede vision. If left untreated, these individuals may be at high risk of progressing to bilateral vision loss. Strategies aiming to ensure that those with unilateral vision loss undergo regular eye examinations and receive necessary treatments, including cataract extractions, may ultimately serve to narrow the gap in indigenous eye health.

The prevalence of diabetes and the resultant vision loss caused by DR are increasing in Australia.³⁷ Therefore, early detection and treatment of DR is becoming an increasingly important component of efforts to reduce the burden of vision loss. This is further supported by the observed association between unilateral vision loss and self-reported diabetes (odds ratio, 1.52; 95% CI, 1.12-2.07; P = .01), and the high prevalence of DR-induced blindness (8.3% of all blindness). Considering that most blindness caused by DR is preventable, the high burden of both unilateral and bilateral vision loss³⁸ in indigenous participants in the NEHS with self-reported diabetes points to insufficient availability or uptake of diabetes-related eyecare services.³⁹ These findings, along with the finding that almost 20% of indigenous unilateral blindness was caused by other retinal diseases, necessitates integrated and sustainable models to ensure regular retinal examinations for indigenous Australians. The recent inclusion of reimbursement for DR screening in the Australian national Medicare universal health care system will support this process.⁴⁰

The prevalence of unilateral vision loss in nonindigenous Australians in the NEHS cannot be readily compared with previous Australian studies as they defined vision loss based on BCVA rather than PVA.^16,18 Additionally, most countries with unilateral vision loss data have used World Health Organization definitions of VI (BCVA <6/18) and blindness (BCVA <3/60), rendering comparisons unreliable.^7,41-43 However, the Icelandic Reykjavik Eye Study used the same definitions as the NEHS and reported a prevalence of 5.45% for unilateral VI compared with a prevalence of 14.6% in the NEHS.¹⁵ This difference may arise in part via sampling differences, with the NEHS selecting participants from all remoteness strata and the Reykjavik Eye Study focusing on metropolitan areas with good access to care. Nonetheless, considering that both Iceland and Australia are developed nations, the finding that unilateral VI is more than twice as prevalent in Australia supports the need for improved service availability and uptake. It should, however, be noted that the prevalence of unilateral blindness in the NEHS was half of that in Iceland (1.4% vs 3.06%). Considering that, compared with unilateral blindness, VI has minimal detrimental effects on quality of life,⁴⁴ prioritizing Australians with unilateral blindness through the provision of low-vision services and the slowing of disease progression may be beneficial. A significant proportion of those with unilateral vision loss, particularly those with cataract, DR, and glaucoma, are at risk of progressing to bilateral blindness if left untreated due to the bilaterality of these conditions.^45,46 Therefore, allocating resources to ensure that those with unilateral vision loss undergo regular eye examinations to ensure treatment of progressive eye diseases, may be an effective public health strategy.

With the exception of AMD, causes of unilateral blindness differed from those of bilateral blindness in nonindigenous participants in the NEHS.⁴⁷ Most saliently, amblyopia was the main cause of 6.4% of VI and 19% of blindness. Amblyopia has frequently been shown to be a major cause of unilateral (but not bilateral) blindness in Australia^16,18 and other countries.^15,48 Trauma (16.7%) was another important cause of unilateral blindness. Amblyopia, trauma, and some corneal conditions are not age-related eye diseases, and their substantial contribution to the burden of unilateral vision loss in this older population may reflect a similarly high prevalence in younger working-aged Australians in whom the disability burden is likely to be greater due to impediments to occupational functioning.

Strengths of this study included the stratified sampling methodology. In addition, the comprehensive ophthalmic examination facilitated disease attribution.

Two important limitations should be considered. First, the cause of unilateral VI and unilateral blindness could not be ascertained for 2.1% to 8.3% of participants, and while these participants were included in the calculation for the prevalence of unilateral vision loss, the cause of their vision loss was recorded as “not determinable” (Table 2). This was often the result of suboptimal retinal image quality owing to small pupil size or inability to fixate. Second, the sample size calculation was not powered to determine the low prevalence of unilateral blindness or disease, but rather the higher prevalence of vision loss in general. Consequently, there is more uncertainty around the cause-specific prevalence estimates and for unilateral blindness.

In summary, while unilateral vision loss has a less severe personal and societal impact than bilateral vision loss, its comparatively higher prevalence in both indigenous and nonindigenous Australians supports the inclusion of unilateral vision loss as a target for national eye health care programs. Approximately three-quarters of unilateral vision loss in Australia could be reversed with integrated spectacle dispensing and cataract services. With the increasing prevalence of DR, cataract, glaucoma, and AMD owing to population aging, those with unilateral vision loss are at risk of progressing to bilateral vision loss because of the bilateral nature of these conditions. Therefore, blindness prevention strategies should allocate sufficient resources to ensure that those with unilateral vision loss undergo regular eye examinations to reduce the burden of VI and blindness in Australia.

Corresponding Author: Joshua Foreman, BSc (Hons), Centre for Eye Research Australia, Level 7, 32 Gisborne Street, East Melbourne, Victoria, Australia 3002 (foreman.j@unimelb.edu.au).

Accepted for Publication: November 28, 2017.

Published Online: January 25, 2018. doi:10.1001/jamaophthalmol.2017.6457

Author Contributions: Mr Foreman and Dr Dirani had full access to the data in the study and take responsibility for the integrity of the data and accuracy of data analysis.

Concept and design: Foreman, Crowston, Taylor, Dirani.

Acquisition, analysis, or interpretation of data: Foreman, Xie, Keel, Ang, Lee, Bourne, Taylor, Dirani.

Drafting of the manuscript: Foreman, Xie, Keel, Dirani.

Critical revision of the manuscript for important intellectual content: Foreman, Xie, Ang, Lee, Bourne, Crowston, Taylor, Dirani.

Statistical analysis: Foreman, Xie.

Obtained funding: Taylor, Dirani.

Administrative, technical, or material support: Foreman, Lee, Crowston, Dirani.

Supervision: Keel, Taylor, Dirani.

Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. No disclosures were reported.

Funding/Support: The National Eye Health Survey was funded by the Department of Health of the Australian Government, and also received financial contributions from the Peggy and Leslie Cranbourne Foundation and Novartis Australia. In-kind support was received from our industry and sector partners, Optical Prescription Spectacle Makers (OPSM), Carl Zeiss, Designs for Vision, the Royal Flying Doctor Service, Optometry Australia and the Brien Holden Vision Institute. The Centre for Eye Research Australia receives Operational Infrastructure Support from the Victorian Government. The work is further supported by National Health and Medical Research Council Career Development Fellowship grant 1090466 (Dr Dirani) and Australian Postgraduate Award scholarship (Mr Foreman).

Role of the Funders/Sponsors: The funders and sponsors of this research had no role in design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

Additional Contributions: The Centre for Eye Research Australia (CERA) and Vision 2020 Australia thank the National Eye Health Survey project steering committee members for their contributions and the core CERA research team who assisted with the survey field work, as well as the collaborating Indigenous Australian organizations that assisted with the implementation of the survey and the indigenous Australian health workers and volunteers at each survey site who contributed to the field work. We would also like to specifically acknowledge the in-kind support of our industry sponsor Optical Prescription Spectacle Makers, which kindly donated sunglasses valued at Aus$130 for each study participant. The core CERA research team and some indigenous Australian health workers were compensated for their labor. All other contributions were uncompensated.