Objective To estimate the prevalence and main causes of blindness and vision impairment in people aged 50 years and older in Papua New Guinea (PNG).
Design National cross-sectional population-based survey in National Capital District (NCD), Highlands, Coastal and Islands regions.
Methods Adults aged 50 years and above were recruited from 100 randomly selected clusters. Each participant underwent monocular presenting and pinhole visual acuity (VA) assessment and lens examination. Those with pinhole VA<6/12 in either eye had a dilated fundus examination to determine the primary cause of reduced vision. Those with obvious lens opacity were interviewed on barriers to cataract surgery.
Results A total of 4818 adults were examined. The age-adjusted and sex-adjusted prevalence of blindness (VA <3/60), severe vision impairment (SVI, VA <6/60 but ≥3/60), moderate vision impairment (MVI, VA <6/18 but ≥6/60) and early vision impairment (EVI, VA <6/12 but ≥6/18) was 5.6% (95% CI 4.9% to 6.3%), 2.9% (95% CI 2.5% to 3.4%), 10.9% (95% CI 9.9% to 11.9%) and 7.3% (95% CI 6.6% to 8.0%), respectively. The main cause of blindness, SVI and MVI was cataract, while uncorrected refractive error was the main cause of EVI. A significantly higher prevalence of blindness, SVI and MVI occurred in the Highlands compared with NCD. Across all regions, women had lower cataract surgical coverage and spectacle coverage than men.
Conclusions PNG has one of the highest reported prevalence of blindness globally. Cataract and uncorrected refractive error are the main causes, suggesting a need for increased accessible services with improved resources and advocacy for enhancing eye health literacy.
- public health
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Vision impairment and blindness are worldwide health concerns affecting 405 million and 36 million people, respectively.1 The most affected communities and countries are those with poor accessibility to services and inadequate resources. The most populous country in the South Pacific is Papua New Guinea (PNG) with over seven million people.2 It is a geographically and sociodemographically diverse country divided into 19 provinces, with over 800 languages each representing a distinct culture. An estimated 87% of the population lives in rural areas, commonly in partial or substantial subsistence.3
The latest vision-related epidemiological study in PNG was conducted over 10 years ago and established a high prevalence of vision impairment (29%) and blindness (3.9%) in older adults.4 However, the study was only conducted in areas within and surrounding PNG’s capital, Port Moresby.
The Rapid Assessment of Avoidable Blindness (RAAB) Survey is an efficient and standardised methodology that can be used to generate population-based evidence on the prevalence and causes of blindness, and assess cataract surgical services for individuals aged 50 years and older.5 The data obtained are commonly used for eye care planning and advocacy.
Due to the absence of any population data related to vision impairment and blindness in the past decade across PNG, new estimates are required to advocate for the development of an appropriate intervention programme. Taking into consideration the geographical and environmental diversity and available eye care services, PNG can be divided into four regions: the Highlands (all provinces within the administrative region), Coastal (provinces within the Momase and Papua administrative regions, excluding Milne Bay), the Islands (all provinces within the administrative region and Milne Bay province) and the National Capital District (NCD). Using the standard RAAB methodology, the aim of this project was to estimate the prevalence and main causes of blindness and vision impairment in people aged 50 years and older in all four regions of PNG.
Materials and methods
This cross-sectional population-based survey was completed in four regions of PNG: Highlands, Coastal, Islands and NCD. With an anticipated prevalence of blindness at 3.9%, at a 95% CI with relative precision of 20%, design effect of 1.5, and dropout rate of 10%, a combined total of 5000 participants, 1250 persons within each region, was required. This sample also provided 80% power at the 5% level of significance to detect a 20% difference in vision impairment between the four regions. Using 2011 census information from the National Statistical Office of PNG, systematic sampling was applied to select 25 enumeration areas (EAs) in each region with a probability proportional to size from a sampling frame of all census EAs in that region. Within each selected EA, 50 adults were recruited through compact segment sampling. Inclusion criteria were adults aged 50 years or older who resided within the selected cluster for at least 6 months. All eligible adults provided written or thumbprint consent to participate.
Two teams for the NCD region and one team for each of the remaining regions were established to complete data collection. Each team consisted of one ophthalmologist, one research assistant and one local eye health worker. Training the survey teams involved explaining the concept and importance of using the RAAB approach to conduct the survey, assessing interobserver agreement on visual acuity (VA) measurement, lens examination and causes for reduced vision.
All participants were interviewed to obtain demographic information and assess spectacle use. Presenting monocular VA was checked in broad daylight using a tumbling E chart. Pinhole monocular VA was checked if presenting VA was <6/12. If pinhole VA was <6/12 in either eye, the participant’s pupils were dilated with 0.5% tropicamide and direct ophthalmoscopy was performed indoors or in a shaded area to determine the cause of reduced vision. If the participant needed cataract surgery, reasons for not having had surgery were elicited. If the participant had received cataract surgery, surgery details and outcomes were surveyed. Participants identified as requiring further eye care were referred to appropriate services.
Data management and analysis
For all regions excluding NCD, data were recorded on mobile phones using the mRAAB app (V.1.30, Peek Vision, UK). In NCD, data were recorded on paper survey forms and double data entry was completed in the RAAB6 software (V.6, London School of Hygiene & Tropical Medicine, UK).
For each region, data were analysed with the RAAB6 software. Outcome measures included the prevalence of blindness (VA <3/60), severe vision impairment (SVI; VA <6/60 but ≥3/60), moderate vision impairment (MVI; VA <6/18 but ≥6/60) and early vision impairment (EVI; VA <6/12 but ≥6/18), the causes of blindness and vision impairment, cataract surgical coverage (CSC), cataract surgical outcomes and barriers to cataract surgery. Data analyses for uncorrected distance refractive error only included participants achieving presenting or pinhole VA ≥6/12; this was to exclude those with vision impairment due to non-refractive causes.
To adjust the outcomes for age and sex, census data available for each region were used. To compare between regions, 95% CIs were assessed for any overlap.
For a national estimate of blindness and vision impairment, CSC and refractive error, the weighted average was calculated based on census information on adults aged 50 years and older in each region. Where applicable, 95% CIs were calculated using the weighted average outcomes and corresponding SEs for cluster sampling. Using the RAAB6 software, SEs were calculated by combining data from the four regions and generating the sampling error and design effect report. P values <0.05 were considered statistically significant.
A total of 4818 participants were examined (96.4% response rate) from the four regions of PNG. The distribution of the sample and survey areas by age and sex are presented in table 1. A significantly greater proportion of older age groups (70–79 years and 80+years) was in the sample in comparison to the population distribution (p<0.001). The over-representation of older groups occurred in all regions except NCD where participants were predominantly aged between 50 years and 59 years. Men were significantly over-represented in the survey population from the Highlands, whereas women were over-represented in NCD, compared with regional distributions (both p<0.001).
Prevalence of blindness and vision impairment—sample and age-adjusted and sex-adjusted outcomes and extrapolation
A total of 225 individuals (6.1%; 95% CI 5.0% to 7.1%) had bilateral blindness, 122 individuals had SVI (3.1%; 95% CI 2.4% to 3.9%), 492 individuals had MVI (11.9%; 95% CI 10.5% to 13.3%) and 365 individuals had EVI (7.8%; 95% CI 6.7% to 8.8%). The estimated age-adjusted and sex-adjusted prevalence of blindness, SVI, MVI and EVI in PNG were 5.6% (95% CI 4.9% to 6.3%), 2.9% (95% CI 2.5% to 3.4%), 10.9% (95% CI 9.9% to 11.9%) and 7.3% (95% CI 6.6% to 8.0%), respectively. Table 2 presents the prevalence and extrapolates the results to estimate the number of men and women with blindness and vision impairment across each region and the country.
Regionally, there was a significantly greater prevalence of blindness, SVI and MVI in the Highlands compared with NCD. Furthermore, a significantly greater prevalence of MVI was observed in the Coastal region compared with NCD and the Islands (table 2). The prevalence of blindness and all levels of vision impairment significantly increased with age (all p<0.001). When comparing genders, there was a significantly greater prevalence of blindness in women (7.0%; 95% CI 6.2% to 7.8%) compared with men (4.4%; 95% CI 3.4% to 5.4%), nationally.
Primary causes of blindness and vision impairment
Table 3 presents the primary causes of blindness and vision impairment of the participants and the national prevalence estimate. Regional data are presented in online supplementary S1. For all regions, the most common cause of blindness (88.6%), SVI (89.3%) and MVI (76.1%) was untreated cataract. Other posterior segment eye diseases were the second most common cause of blindness (3.9%). Uncorrected refractive error was the main cause of EVI (45.3%).
CSC and outcomes
Nationally, CSC (VA<6/60) was 32.3%, but ranged from 9.2% (women in the Highlands) to 78.3% (men in the Islands). At all levels of VA, CSC was significantly lower in women compared with men in the Highlands (table 4). The Islands had significantly higher CSC compared with all other regions (65.8% compared with 18.1%–35.9%, p<0.001).
Over 60% of the cataract operated eyes resulted in a good visual outcome (VA ≥6/18) with best corrected VA (table 5). However, a quarter of operated (25.1%) eyes resulted in a poor visual outcome (VA <6/60). Of those who had poor cataract surgical outcomes, 53.3% had long-term complications such as posterior capsular opacification or retinal detachment, 28.3% had operative complications and 18.3% had ocular comorbidities.
Barriers to cataract surgery
The reported barriers to cataract surgery varied between sexes and regions. Although not statistically significant, more women than men reported that they were ‘unaware (cataract) treatment is possible’ (37.6% vs 31.5%, p>0.05) or that a ‘need (was) not felt’ for surgery (36.1% vs 30.9%, p>0.05). These barriers to cataract surgery were the most commonly reported in all regions except the Coastal region, where cost was considered the most prominent barrier reported (cost: 35.0%, unaware treatment possible: 13.8%, need not felt: 16.3%).
Uncorrected refractive error
The weighted average prevalence of distance refractive error was 8.2% (95% CI 6.7% to 9.7%) in adults aged 50 years and older. The Highlands (4.3%, 95% CI 3.1% to 5.5%) had a significantly lower prevalence of distance refractive error compared with the other regions (NCD 10.2%; 95% CI 8.0% to 12.3%; Coastal 11.4%; 95% CI 7.6% to 15.3%; Islands 11.1%; 95% CI 9.1% to 13.2%). Uncorrected distance refractive error was 72.7%, where a significantly higher proportion of women were uncorrected compared with men (61.3% vs 79.1%, p<0.001).
The estimated age-adjusted and sex-adjusted prevalence of blindness in people aged 50 years and older in PNG is 5.6% (95% CI 4.9% to 6.3%). Although not significant, this is higher than the previous estimation of 3.9% (95% CI 3.4% to 6.1%).4 However, comparisons are to be taken with caution as this survey recruited individuals from all provinces within PNG, while the previous survey recruited individuals who were from one urban and one rural community. In comparison to previous RAABs, the prevalence of blindness in PNG is one of the highest in the world—blindness in other countries range from 0.4% (Occupied Palestinian Territories) to 7.5% (Eritrea).6–15
The main causes of blindness and vision impairment in PNG are cataract and uncorrected refractive error. Previously, untreated cataract was reported to cause 73.2% of blindness.4 When compared with this study (81.8% in NCD and 91.0% in Coastal regions), the difference could be a reflection of the more remote and rural locations surveyed where accessibility to cataract services are likely to be limited. Distance refractive error in older adults was estimated to be 8.2% (95% CI 6.7% to 9.7%), where only 31.5% within the sample had appropriate correction. Similarly, the higher prevalence of blindness in the Highlands compared with elsewhere, may reflect broader health disparities experienced by Highlanders.16
Gender differences were observed in CSC and spectacle coverage with lower occurrencess in women across all regions. Similar gender differences have been observed in other developing countries.17 Previous reports on female attitudes towards eye care in PNG have included fear of jealousy and feelings of shame with spectacle wear.18
WHO recommends using CSC as it informs the degree to which cataract services are meeting population needs.19 Based on available RAAB data, the median CSC is 53.7 for operable cataracts (pinhole VA <6/60) across low-income, middle-income countries in Asia, Africa and South America.20 PNG had an estimated combined national CSC of 32.3%. Although CSC was lower than the calculated median, a wide range was observed. Previous and current CSCs in NCD and Coastal regions combined were reported to be 45.3% and approximately 35%, respectively.21
WHO currently recommends cataract surgical outcome targets to be at least 80% of operated eyes to have presenting VA ≥6/18 and at most 5% postoperative presenting VA <6/60.22 We found that PNG is below the recommended target. However, as several countries are yet to reach the recommended cataract surgery outcome targets,20 our findings are similar to other low-income, middle-income countries, indicating the continuing need for increased surgical coverage and improved outcomes potentially through increasing resources, training and personnel. Currently there are 14 practising ophthalmologists and 5 in training, most of which are based in more urban areas. Outreach services are available only to some regions and are on an ad hoc basis. Yet, increasing resources might only partially improve outcomes where other barriers exist. Difficult terrain and the absence of road infrastructure hinder patients travelling to health facilities.23 Limited access to postoperative treatments might contribute to poorer than expected long-term outcomes.
The commonly reported barriers to cataract surgery such as ‘unaware treatment is possible’ and ‘need not felt’ highlights the need for improving eye health education among the older population in PNG. In particular, focus should be placed on increasing awareness on the availability and potential benefits of cataract surgery. In the Coastal region, cost was the most commonly reported barrier to accessing cataract surgery. As cataract surgery is heavily subsidised by the PNG government, cost barriers might be a reflection of many people in this region needing to travel to the NCD for treatment, thus incurring additional travel and accommodation expenses.
Distance spectacle coverage was 27.3%, which is lower than reports from India (28.4%), but higher than Timor-Leste (15.7%).24 25 The addition of EVI to the survey has highlighted the demand for refractive services across the whole nation.
Despite the many logistical, geographical and security issues faced in conducting a survey of this nature in PNG, there was a high response rate, low missing data and high coverage. However this study also has some limitations. The high prevalence of blindness and vision impairment observed is only applicable to older adults in PNG and cannot be generalised to those aged under 50 years. However, including younger age groups would significantly increase the sample required as the prevalence of blindness is often lower in the young population.26 With the exception of NCD, the over-representation of older age groups of 70–79 years and 80+years in the three regions might have led to an overestimation of the sample prevalence for blindness and vision impairment. However, adjusting for age and sex in each of the four regions mitigated the impact of over-representation on the estimates.
This is the first national population-based assessment of blindness and vision impairment in PNG. The high prevalence of blindness, largely due to cataract, suggests the need to address the availability, accessibility and uptake of cataract surgical services and increase efforts to educate older patients on avoidable blindness. Furthermore, the low coverage of corrected refractive error underpins further development of refractive services in PNG. There is a particular need for services for women across the country, and people in the Highlands.
The authors thank the fieldwork survey teams for travelling across the country and enduring the tough conditions in order to complete data collection. The authors also thank Thomas Naduvilath for assistance with statistical analysis.
Contributors LL, JG, GW, SPK, DK, ATC, HL and AB designed and conducted the survey. LL, FD'E, HL and AB analysed the data. LL, FD'E and AB prepared the manuscript. All authors edited and reviewed the manuscript, and agree with the final version of the manuscript and agree to be accountable for all aspects of the work.
Funding The Fred Hollows Foundation, Australia.
Disclaimer This work is original, has not been published and is not being considered for publication elsewhere. There are no conflicts of interest for any of the authors that could have influenced the results of this work. All authors have contributed significantly to the project and subsequent drafting, revising and approval of the final version submitted.
Competing interests None declared.
Patient consent Obtained.
Ethics approval Medical Research Advisory Committee of PNG (MRAC No.16.35), the Milne Bay Provincial Research Committee (DPA: 3-15) and The University of New South Wales Human Research Ethics Committee (HC16804).
Provenance and peer review Not commissioned; externally peer reviewed.