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Abstract
Background To determine the prevalence and causes of visual impairment (VI), and to describe the characteristics of cataract surgery coverage and related barriers among adults aged ≥50 years residing in Hohhot, Inner Mongolia.
Methods A population-based cross-sectional study was performed. Presenting visual acuity (PVA) was measured using the Rapid Assessment of Avoidable Blindness (RAAB) methodology. All VI cases were defined using the WHO definition, based on the PVA of the better-seeing eye. Details on history of cataract surgery and barriers to cataract surgery were also obtained using a standardised questionnaire.
Results Of 4500 eligible individuals, 3985 (88.6% response rate) were examined. The age-standardised prevalence of moderate VI (PVA <6/18 to ≥6/60) was 5.4% (95% CI 4.6% to 6.3%), and severe VI (PVA <6/60 to ≥3/60) was 0.9% (95% CI 0.6% to 1.3%). The age-standardised prevalence of blindness (PVA <3/60) was 1.2% (95% CI 0.8% to 1.6%). Uncorrected refractive error (40.1%) and cataract (37.9%) were the leading causes of overall VI. Cataract (34.9%) was the leading cause of blindness. Among individuals with blindness, cataract surgical coverage was 80.7%. Among individuals with blindness due to cataract, the main barriers to cataract surgery were lack of awareness (38.1%).
Conclusions The age-standardised prevalence rate of blindness in Hohhot was lower compared with other RAAB studies in China. Cataract was the leading cause of blindness. These findings provide useful information for the planning of public healthcare services in Inner Mongolia.
- visual impairment
- blindness
- cataract
- low vision
- population
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Introduction
Visual impairment (VI), including low vision and blindness, is a main public health concern in China.1 2 A population-based survey in Baotou, Inner Mongolia, was conducted recently to evaluate the prevalence of VI. According to this report, VI was more prevalent among elderly people and in individuals with low education level. In addition, cataract was reported to be the main cause for VI.3 Another study in Kailu, northern Inner Mongolia, reported that the prevalence of blindness and VI based on best-corrected visual acuity (BCVA) was 0.9% and 4.7%, respectively. The leading cause of VI and blindness in Kailu was also cataract.4 However, barriers to cataract surgery and cataract surgery-related outcomes were not investigated in these previous studies. Taken together, there are still limited data and information on VI-related and cataract surgery-related trends in the vast region of Inner Mongolia. Hence, further evaluation on the trend of VI in Inner Mongolia is needed.
Hohhot is a city in Inner Mongolia that constitutes mainly Mongols and other ethnicities such as Han, Hui, Manchu, Daur and Evenki. Differences in lifestyles and cultures are well noted across these ethnicities, and it is plausible that these multiethnic differences may result in different patterns of VI in Hohhot compared with other areas in China.
The purpose of this research was to investigate the prevalence and causes of VI, and to describe the characteristics of cataract surgery coverage and related barriers in an adult population aged ≥50 years in Inner Mongolia. Findings from our study will help to further improve the understanding on the trends of VI in Inner Mongolia and will be useful in the planning of public health initiatives, allocation of resources and deployment of health services.
Methods
Study population
Hohhot is a city in north China and the capital of the Inner Mongolian Autonomous Region, serving as the region’s administrative, economic and cultural centre. The total area of the city is 17 000 km2, holding a population of 2 147 000 in 2013, 1 096 400 of which reside in urban areas.
There are four municipal urban districts (Hui District, Yuquan District, New Town, Saihan District), five rural counties (Tuoketuo County, Qingshuihe County, Wuchuan County, Lingel County) and one Banner (Tumote Zuo Banner) in Hohhot.
The sample size of this study was determined with an expected prevalence of VI of 9%,5 precision 20% with 95% error bound and 10% non-response rate, based on the formula
Using this formula, the sample size was calculated to be 4500 individuals. A multistage sampling method was performed to select the subjects. A total of 10 clusters were randomly selected from each of the nine study locations. For the analysis, each cluster was required to contain at least 50 individuals aged 50 years and above. Municipal and village’s staff offices were used as clusters in urban and rural location, respectively.
Five teams were trained for 2 weeks to perform the required examinations on the study participants. Each of the five teams consisted of three ophthalmologists and two nurses. These teams carried their own equipment to the cluster locations. The equipment included ‘E’ visual testing charts, a slit lamp and a non-mydriatic fundus camera (Topcon, Tokyo, Japan).
This study was approved by The Chao Ju Eye Hospital Institutional review board, and the conduct of the study adhered to the Declaration of Helsinki. Before starting the eye examination, the research team explained the study procedures to the subjects and written informed consent was then obtained from each participant or his/her family member. Data collection for this study was carried out from April to October 2014.
Ocular examination
Visual acuity (VA) testing and other eye examinations were performed using the Rapid Assessment of Avoidable Blindness (RAAB) protocol (https://www.bicomalawi.org/manuals/_RAAB_instruction_manual.pdf). RAAB is a survey on VI and eye healthcare services for people aged ≥50 years, and is endorsed by WHO.6 Each participant was evaluated by two ophthalmologists. In the event where examination findings were inconsistent between the two ophthalmologists, another experienced ophthalmologist examined the patient again and made final decision for the participant.
Each participant was also interviewed to complete the RAAB assessment and survey form. Presenting visual acuity (PVA) of each eye was examined separately. In the event where PVA was worse than 6/18, VA was measured again using pinhole, and the pinhole VA was taken as the final VA measurement.
The ocular surface, anterior segment and lens were assessed using a slit lamp without pupil dilation. For subjects with pinhole VA less than 6/18, the pupils were dilated with a combination of 0.5% tropicamide and 1% phenylephrine eye drops for detailed fundus examination using a fundus camera, unless shallow anterior chamber was present. The main cause of VI was determined according to the examination outcomes. A standardised questionnaire was used to obtain information on the history of cataract surgery. In addition, among subjects identified with VI due to cataract, a questionnaire on barriers to cataract surgery was completed.
Definitions
In this survey, the WHO definition was used to define VI, based on the better-seeing eye. Blindness was defined as PVA <3/60, severe VI (SVI) was defined as PVA <6/60 to ≥3/60 and moderate VI (MVI) was defined as PVA <6/18 to ≥6/60. Low vision was defined to include both MVI and SVI categories. The postcataract surgery visual outcome (based on PVA) was divided into four categories: excellent (≥6/12), good (<6/12 to ≥6/18), fair (<6/18 to ≥6/60) and poor (<6/60). Cataract surgical coverage is the indicator used to assess the level to which cataract surgery needs have been met. Cataract surgical coverage was calculated in a standard way by the RAAB software (http://raabdata.info/downloads/).
Statistics
RAAB software (http://raabdata.info/downloads/) was used to enter and analyse the data for prevalence of blindness, SVI, MVI and the aetiologies of VI. The prevalence rate was calculated and presented with 95% CIs. Detailed statistics regarding outcomes of cataract operations, cataract surgery coverage and barriers to cataract operations were described previously.7 In order to facilitate comparison with other studies, age-standardised prevalence was calculated according to the 2010 Population Census of The People’s Republic of China (www.stats.gov.cn/tjsj/pcsj/rkpc/6rp/indexch.htm). Age-standardised prevalence rates were calculated using R software V.3.3.1 (R Foundation for Statistical Computing, Vienna, Austria).
Results
There were 4500 subjects aged ≥50 years enumerated in the survey, of whom 3985 (response rate, 88.6%) completed the ocular examination. Table 1 shows the coverage, absenteeism and refusals. Overall, 4.8% were not available, 6.1% refused and 0.5% were not capable of completing this survey. The crude prevalence rates of MVI, SVI and blindness were similar between men and women (table 2).
Demography of coverage, absenteeism and refusals, n (%)
Overall crude prevalence of low vision and blindness, stratified by gender
Table 3 showed that the age-standardised prevalence rates of MVI, SVI and blindness in the examined population were 5.4% (95% CI 4.6% to 6.3%), 0.9% (95% CI 0.6% to 1.3%) and 1.2% (95% CI 0.8% to 1.6%), respectively. Cataract (46.3%) and uncorrected refractive error (39.4%) were the two main causes for MVI. However, uncorrected refractive error (36.4%) was the principal cause for SVI, followed by cataract (33.3%). In addition, cataract (34.9%) and posterior segment disease (30.2%) were the leading causes of blindness (table 4).
Prevalence of low vision and blindness stratified by age groups
Primary causes of visual impairment
The cataract surgical coverage rate was 80.7% among individuals with blindness, 74.0% among those with SVI and 48.3% among those with MVI. A total of 189 eyes (131 individuals) were reported to have history of cataract surgery, of which 102 eyes (53.9%) underwent cataract surgery in government hospital, 36 eyes (19.1%) in charitable organisation and 51 eyes (27.0%) at private hospital. Among these three cataract surgery sites, government hospital (10.8%) had the lowest proportion of poor postcataract surgery visual outcome (PVA <6/60). In addition, the proportion of excellent postcataract surgery visual outcome (PVA ≥6/12) in government hospital, charitable organisation and private hospital was similar, ranging between 55.6% and 59.8% (table 5). Among individuals with blindness due to cataract, the main barriers to cataract surgery were lack of awareness (38.1%) and lack of accessibility to treatment (14.3%).
Postoperation visual acuity with available correction, stratified by treatment place of cataract surgery
Discussion
To the best of our knowledge, this is the first survey that investigated the prevalence and main causes of VI, and further evaluated cataract surgery-related outcomes and barriers to accessing cataract surgery in a population aged ≥50 years in Inner Mongolia. In this survey, we found that the age-standardised prevalence rates for moderate, severe VI and blindness were 5.4%, 0.9% and 1.2%, respectively, in Hohhot. Uncorrected refractive error (40.1%) and cataract (37.9%) were the leading causes of overall VI, and cataract (34.9%) was the leading cause of blindness. In addition, cataract surgical coverage among individuals with blindness was 80.7%, and the main barrier for accessing cataract surgery was lack of awareness for cataract.
The crude prevalence rate of blindness (1.1%) in our study was similar to those found in other Inner Mongolia population-based studies (1.0% in Baotou study and 0.9% in Kailu study, based on BCVA).3 4 On the other hand, the prevalence of low vision (5.7%) in our study was slightly higher than those in Baotou (3.7%)3 and Kailu (4.7%).4 Nevertheless, the study sample for Baotou and Kailu studies were aged 40 years and above.
To facilitate comparison with other RAAB studies, we calculated the age-standardised prevalence of VI in other RAAB surveys using the China National Population Census 2010. The relevant data were either extracted from published papers7–9 or from the RAAB data repository (http://raabdata.info/repository). We observed that the age-standardised prevalence of MVI, SVI and blindness in Hohhot was lower than the estimates from studies in Hainan and Kunming (table 6). This may be because both studies of Hainan and Kunming were conducted in rural areas, whereas our survey consisted of a mixed rural and urban population. Prevalence of VI and blindness in rural areas were generally higher than in urban areas.10 In addition, lower socioeconomic status had been shown to be associated with higher prevalence of VI.11 12 In this regard, a recent report showed that the gross domestic product of Inner Mongolia Autonomous Region was higher than Hainan and Yunnan (Kunming is the capital of Yunnan province) (http://epaper.21jingji.com/html/2017-02/07/content_55506.htm). This may partially explain the lower prevalence of VI in Hohhot.
Comparison of the surveys evaluated the prevalence of VI and blindness in China using RAAB
However, the age-standardised prevalence rates of MVI, SVI and blindness in our study were similar to those obtained from the Jiangxi study, which comprised three counties of Gao’an, Xin’gan and Wan’zai of Jiangxi Province, China.9 The Jiangxi study was also performed in rural areas, of which two counties (Gao’an and Xin’gan) were part of the Fred Hollows Foundation (FHF) programme: a non-profit aid organisation. The FHF programme focuses on treating and preventing blindness and other visual diseases, by establishing an effective patient referral network, physician training plan and community vision screening projects. This may partially explain the lower rates of low vision and blindness in Jiangxi study, even though the study was conducted in a rural area.9 However, the exact reasons for different prevalence rates of VI and blindness across these studies are still unclear and may warrant further comprehensive investigations in the future.
In our study, we observed that cataract is the main cause of VI and blindness. Nevertheless, the cataract surgery coverage rate reported in this study was lower than other countries.13 This highlights the need to further enhance the coverage of cataract surgery in Hohhot. Although there are increasingly more private hospitals and charitable organisations in China carrying out cataract surgery, and the cost of surgery can be lower than that in government hospital, our survey found that most participants still preferred to undergo cataract surgery in government hospitals. In addition, the proportion of the ratios for excellent postcataract surgery visual outcome (PVA ≥6/12) was similar across government, private hospitals and charitable organisations. However, government hospital had the lowest proportion of poor postcataract surgery visual outcome (PVA <6/60). In contrast, another RAAB survey in Hainan, China, revealed that eyes that underwent surgery in public or private hospitals had a higher proportion with borderline and poor outcomes (PVA <6/18) compared with those operated in charitable organisations (approximately 50% vs 26%).7 With regards to the barriers to cataract surgery, lack of knowledge and awareness about cataract were identified as the main barriers, similar to what has been reported in previous studies performed in other developing countries.14 15 Thus, there remains a need to promote public awareness on cataract. Moreover, limited medical facilities, resources and economic problems are also barriers to cataract surgery. This highlights that more efforts need to be made in order to better improve accessibility to cataract surgery in this population.
The strengths of our study include providing comprehensive information on cataract surgery-related outcomes in northern China, which is currently lacking. Furthermore, we also provided an overall comparison of the age-standardised prevalence rates of VI and blindness with other RAAB studies in China. Nevertheless, there are a few limitations. First, we only compared our findings with other relevant RAAB studies in China. Second, this survey did not evaluate the causes of posterior segment diseases in detail as the design of RAAB study was primarily focused on determining the causes of avoidable VI and blindness. Therefore, further survey focusing on detailed posterior segment assessment may still be needed in the future. Third, subjective refraction was not part of the RAAB methodology and was not performed in this study, thus BCVA measurement data were not obtained, limiting our evaluation to PVA. Finally, the RAAB survey was mainly based on self-report response and may be subjected to recall bias.
In summary, this investigation in Inner Mongolia on adults aged 50 and above showed relatively lower prevalence of low vision and blindness, compared with previous RAAB studies in China. The main causes of VI were avoidable, and thus further patient education and better allocation of medical resources may help to reduce the prevalence of VI in this population. These results will provide useful information for the future planning of public healthcare services in Inner Mongolia.
Acknowledgments
The authors acknowledge the nurses and other paramedical staff, government staff and even drivers during this investigation. The authors acknowledge all the Investigators of the Rapid Assessment of Avoidable Blindness surveys in Hohhot.
Footnotes
HZ and LL contributed equally.
Contributors GZ designed the study protocols. HG, FR and JM performed the data collection and input. LL, Y-CT and C-YC drafted the paper. WD, HZ and LL guided and amended the paper writing. GZ was the study team trainer and commented on the draft paper.
Funding The study was supported by the National Natural Science Foundation of China (no. 81300783), Liaoning Science and Technology Project (no. 2013225303) and Liaoning Provincial Department of Education (no. LQNK201703).
Competing interests None declared.
Patient consent Obtained.
Ethics approval Chao Ju Eye Hospital Research Proposal.
Provenance and peer review Not commissioned; externally peer reviewed.
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