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Prevalence and incidence of presbyopia in urban Southern China
  1. Xiaotong Han1,2,
  2. Pei Ying Lee2,
  3. Stuart Keel2,
  4. Mingguang He1,2
  1. 1 Department of Preventive Ophthalmology, State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangdong, China
  2. 2 Department of Surgery (Ophthalmology), Centre for Eye Research Australia, University of Melbourne, Melbourne, Australia
  1. Correspondence to Dr Mingguang He, Zhongshan Ophthalmic Center, Guangzhou 510620, People’s Republic of China; mingguanghe{at}gmail.com

Abstract

Aims To investigate the prevalence and incidence of presbyopia in an urban Chinese population.

Methods 1817 subjects aged ≥35 years were identified by random cluster sampling in Yuexiu District, Guangzhou, China, at baseline in 2008, and all were invited for the follow-up examination in 2014. Distance and near visual acuity (VA) tests, as well as non-cycloplegic automated refraction were performed at each examination as per standardised protocol. Participants with presenting near VA ≤20/40 were further tested with add power at a standard distance of 40 cm to obtain their best-corrected near VA. Functional presbyopia was defined as near VA under presenting distance refraction correction of <20/50 and could be improved by at least one line with add power.

Results A total of 1191 (83.5% of the 2014 follow-up) participants were included in the current analysis with a mean (SD) age of 50.4 (9.7) years, and 52.9% were female. Prevalence of functional presbyopia at baseline was 25.2% (95% CI 21.5 to 28.9) and the 6-year incidence was 42.8% (95% CI 39.4 to 50.1). Older and more hyperopic subjects had both higher prevalence and incidence of presbyopia (P<0.001). Average presbyopic correction coverage (PCC) was 87.7% at baseline and was significantly lower in myopic participants (P=0.006).

Conclusions Prevalence of functional presbyopia in urban China is relatively lower along with a higher PCC compared with previous population-based rural cohorts. We identified a high presbyopia incidence, and further studies are needed to understand longitudinal presbyopia progression as well as the urban–rural gap in presbyopia to throw light on future strategic planning.

  • epidemiology
  • vision
  • public health

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Introduction

Presbyopia is an inevitable consequence of ageing, commencing in the fourth decade of life.1 The most important mechanism for accommodation loss associated with presbyopia is believed to be an increase in lenticular stiffness.2 Presbyopia not only results in poor near visual function but also severely impacts daily activities and overall quality of life in both developing and developed countries.3 4 Frick et al reported that nearly 1.272 billion people had presbyopia worldwide in 2011, and presbyopia posed a significant financial burden, with estimated productivity loss of US$11.023 billion. Due to population growth and an ageing population, it is estimated that 1.8 billion people will have presbyopia by the year 2050.5 6

Presbyopia has been increasingly recognised as an important public health problem in this ageing society; however, policymaking is hindered by a paucity of recent population-based data. Functional presbyopia is defined as needing a significant add power to the presenting distance refraction correction to improve near visual acuity (VA) by at least one line. This definition has been adopted in previous studies with the reported prevalence ranging from 35.1% in Southern India to more than 67.3% in Northern China; meanwhile, the presbyopic correction coverage (PCC) was reported to be relatively low, ranging from 5.4% in Kenya to 51.5% in Beijing.7–9 To date, most studies investigating the prevalence of presbyopia were conducted in rural areas, and therefore the extent to which the findings can be extrapolated to the general population is limited.7 10 Based on the WHO estimation, the global urban population will grow 1.63% per year between 2020 and 2025.11 China, with a population of 1.38 billion and 42.6% aged 40 years or older, is in urgent need of data on the prevalence and incidence of presbyopia. This particularly applies to urban areas where 57.4% of the population currently reside and will continue to grow with the urbanisation process.12

This study aimed to investigate the prevalence, PCC and 6-year incidence of presbyopia in urban Southern China. This information is important to estimate the disease burden and for effective planning for eye healthcare strategies in the future.

Methods

Study population

The Yuexiu district of Guangzhou is a large urban area (9.16 km2) in Southern China, with an estimated population of 10.18 million (2008).12 Subjects residing in this district, aged 35 years or older, were selected and recruited by random cluster sampling in 2008. Demographic information including age, gender and educational level were documented. Details of the sampling and recruitment methodology have been reported elsewhere.13 14 Briefly, 1817 subjects were enrolled at baseline and all were invited for the 6-year follow-up examinations in 2014. Baseline and follow-up examinations took place at Zhongshan Ophthalmic Center (ZOC) or in local community facilities or homes for individuals with mobility restrictions or limited free time. Same procedures and protocols were applied throughout the baseline and follow-up examinations. Written informed consent was obtained from all participants and the study was conducted in accordance with the tenets of the Declaration of Helsinki. The participants did not receive any financial compensation.

Procedures

Questionnaires including information on detailed ophthalmic surgical history were administered by trained nurses at both baseline and follow-up examinations. Distance and near VA were measured indoor under ambient lighting with a LogMAR ETDRS tumbling E chart (Precision Vision, La Salle, Illinois, USA) as per standardised protocol. Participants with presenting near VA ≤20/40 underwent near add measurement by increment of add power at a testing distance of 40 cm to obtain their best-corrected near VA. Non-cycloplegic automated refraction was carried out for all participants at baseline and follow-up using the same device after proper calibration (KR-8800; Topcon Corp, Japan). Five consecutive measurements were performed for each eye with the mean recorded as the final value. Slit-lamp examination of the anterior segment were performed by an ophthalmologist throughout the study.

Definitions

In accordance with the previous studies, functional presbyopia was defined as binocular near VA <20/50 (N8) at 40 cm with presenting distance refraction correction and improved by at least one line with add power.6 8 The incidence of presbyopia was calculated as the percentage of participants without functional presbyopia at baseline who developed presbyopia during the follow-up period. The ‘met need’ for presbyopia was defined as those with functional presbyopia who had spectacles which could improve their near VA to ≥20/50. The ‘unmet need’ was defined as those with functional presbyopia but without spectacles or unable to reach a near VA of 20/50 with current spectacles. PCC was calculated as the number of ‘met need’ divided by the total number of presbyopia according to previous studies.8 15

Data management and analyses

Spherical equivalent (SE), calculated as spherical power plus half of cylindrical power, was used to represent refraction. Baseline refractive state was categorised into moderate to high myopia (SE<−3 diopters, D), mild myopia (−3D≤SE<−0.5D), emmetropia (−0.5 D≤SE≤+0.5 D) and hyperopia (SE>+0.5 D). Age was categorised into four age groups: 35–44, 45–54, 55–64 and ≥65, based on age obtained at baseline. Education level was dichotomised as less than high school and high school or above. Participants who had undergone refractive surgeries or were aphakic or pseudophakic at baseline or during follow-up period were excluded. Eyes with presenting binocular distance VA <20/63 at baseline or follow-up visit were also excluded. Near VA with presenting distance refraction correction were not available for 96 and 12 participants who had both distance and near vision glasses at baseline and 2014 follow-up, respectively. Uncorrected near VA was used as substitute for this small group of participants.

All statistical analyses were performed using STATA Statistical Software V.12.0. Group t-test and trend analysis were used to assess the difference between participants included and not included in the analysis, as well as the difference in prevalence and incidence of functional presbyopia in different age, gender, education and refraction groups. Χ2 test was used to assess the difference between PCC distributions among different groups. Univariate and multiple regression analysis were used to assess the association between incident presbyopia and potential risk factors. P values of <0.05 were considered statistically significant.

Results

A total of 1427 (78.5% of baseline) participants attended the 2014 follow-up examination. Of which, 172 participants with presenting distance VA <20/63 and 64 participants who had undergone refractive surgery or with aphakic or pseudophakic eyes at baseline or during the follow-up period were excluded. As a result, 1191 (83.5% of 2014 follow-up) participants were included in the current study with a mean (SD) age of 50.4 (9.7) years, and 52.9% were female. A comparison of key demographics between participants who were included and those not included in the analysis is shown in table 1. Those included were significantly younger, with higher education and better near VA (P<0.001).

Table 1

Comparison of participants included and not included in the analysis

The overall prevalence of functional presbyopia at baseline was 25.2% (95% CI 21.5 to 28.9) and no gender difference was observed (table 2). Older and more hyperopic subjects had higher prevalence of presbyopia (P<0.001). Distribution of ‘met need’ and ‘unmet need’ presbyopia as well as PCC at baseline is shown in table 3. Average PCC for the population was 87.7% and was significantly higher in hyperopic participants (P=0.006).

Table 2

Prevalence of functional presbyopia at baseline

Table 3

Presbyopia spectacle correction coverage at baseline

As shown in table 4, the 6-year incidence of functional presbyopia for the 891 participants without presbyopia at baseline was 42.8% (95% CI 35.4 to 50.1) and was higher in older and more hyperopic subjects (P<0.01). Compared with emmetropes, participants with mild myopia had much lower incidence of presbyopia (P<0.001), while participants with moderate to high myopia had a similar incidence. In the multiple regression model, older age (P=0.02), more hyperopic baseline refractive error (P<0.001) and worse baseline near VA (P<0.001) were associated with a higher incidence of presbyopia (table 5).

Table 4

Six-year incidence of functional presbyopia

Table 5

Associations between incident functional presbyopia with sociodemographic factors and baseline near vision

Discussion

This study presents the prevalence, PCC and 6-year incidence of functional presbyopia in an urban Chinese population. The authors are unaware of any published data on incidence of presbyopia. Strengths of this study include its population-based design and the standard methodology at baseline and follow-up examinations.

Population-based studies on the prevalence of presbyopia have been mainly limited to rural areas. The overall prevalence of functional presbyopia in urban China based on our results was 25.2%, which is much lower than the previously reported prevalence in rural Tanzania (61.7%), rural India (35.1%) and rural China (67.3%).7–9 The Shahroud Eye Cohort Study represented a mean socioeconomic status of Iran and reported a prevalence of 58.15%.16 The Andhra Pradesh Eye Disease Study recruited participants from one urban and three rural areas in south India, and the average prevalence of presbyopia was 55.3%.17 A threefold increased risk of presbyopia in town-dwellers compared with village-dwellers had been identified, and rural residence was associated with a higher prevalence of presbyopia in south India.7 17 The population of our study are representative of middle-high level socioeconomic population in urban China with a prevalence lower than all the above studies. This suggests that rural areas have a higher demand of resources compared with urban areas and with the ever growing urban population, more studies are warranted to further elucidate the urban–rural gap.

Given the increasing prevalence of myopia in Asian countries,6 functional presbyopia was assessed in our study as it had been suggested by Holden as the most practical reflection of habitual near vision. Several other studies have reported the prevalence of objective presbyopia, defined as requiring a significant add power (≥1D) to the best distance refraction correction to improve near VA to ≥20/50. If the prevalence of presbyopia was recalculated according to the definition of objective presbyopia, the overall prevalence of presbyopia would be slightly higher. This is due to the fact that 17.4% of the population in this study had mild myopia, and only 16.9% of them had presenting distance glasses. Therefore, it should be noted that direct comparisons of the prevalence of presbyopia between previous studies can be problematic due to significant differences in age distributions, socioeconomic status and definitions utilised.

Unlike previous international researches, we did not find any associations between gender and presbyopia.7 17 18 However, our findings are consistent with epidemiological data derived from rural northern China.8 Women and men had similar presbyopia incidence according to our results, which further suggests that there is no gender difference for presbyopia in Chinese population. This difference may be attributed to the higher prevalence of hyperopia in Caucasian and African women,18 19 while no such gender difference had been reported in the Chinese population.19 20 Association between education and presbyopia was inconsistent in literature. Unlike previous studies in Tanzania and India, we did not report an association between both the prevalence and incidence of presbyopia and educational level.7 9 This may be explained by the fact that most previous studies failed to take refractive error into consideration while evaluating the association between education and presbyopia. Given mild myopes were found to have a significantly lower prevalence and incidence of presbyopia, the effect of education on presbyopia may be explained by more myopes in higher education groups.

Despite advancements in presbyopia treatment, including corneal inlays, presbyopic laser in situ keratomileusis and non-invasive pharmacological treatment, spectacles remain the most cost-effective option for the general population.21 22 In the current study, nearly 90% of the population had effective presbyopic correction spectacles. This is similar to that reported in developed countries such as Australia and Finland,23 24 and notably higher than previous population-based reports from Timor-Leste (26.2%), rural India (43.2%) and rural northern China (51.5%).7–9 This is suggestive of higher availability and utilisation of refractive services in more developed areas. Furthermore, participants with myopia were less likely to have spectacles for presbyopia in our analysis. This is consistent to a Singapore study which found that more than half of those who did not have near correction were myopic.25 Reluctance to have two pair of glasses and the ease of removing distance correction for near work in myopic subjects might be the reason.

Incidence of functional presbyopia was relatively high (42.8%) in our study. Participants in the 35–44 age group were less likely to have incident presbyopia compared with the ≥45 age group. Cohort effect with higher prevalence of myopia in younger cohorts might explain this, as it was also shown in our data that participants with mild myopia had lower incidence of presbyopia. In addition, the real incidence of presbyopia is higher than that would be expected from our prevalence data, which further suggests cohort effect and that more studies are needed to investigate the true progression rate of presbyopia. Associations between refractive state and presbyopia have been rarely reported in the literature. We report a higher prevalence and incidence of presbyopia in hyperopes, which is not unexpected as subjects with hyperopic refraction employ their accommodation earlier and more frequently and thus more susceptible to presbyopia. Interestingly, participants with moderate to high myopia had higher prevalence and incidence of presbyopia compared with emmetropes, though not at statistically significant level, suggesting that the slower progression of presbyopia is limited to mild myopes. We speculate that this may be due to a tendency for subjects with mild myopia to exert less accommodation during daily life and thus their accommodation ability is better preserved. In consideration of the small sample size in the moderate to high myopia group, further research is warranted to elucidate this finding.

Key limitations of this study must be noted. First, uncorrected near VA, instead of near VA under presenting distance refraction correction was used for analysis in 96 and 12 participants at baseline and 2014 follow-up, respectively. This may have led to an overestimation of the true prevalence and incidence of presbyopia in Chinese adults. However, given that this is less than 10% of the total population, we speculate the influence would be small. Furthermore, we excluded participants who had a presenting distance VA of <20/63 to minimise effect from non-presbyopia vision threatening eye diseases. If included, the observed prevalence of presbyopia would be lower as many of these patients would not have near VA improvement with near correction.

In conclusion, we identified a lower prevalence of functional presbyopia and higher PCC in urban China compared with previous population-based reports in rural areas. Incidence of presbyopia was found to be high and data from more studies are needed to better understand presbyopia progression. Results of our studies are of pragmatic use for planning future strategies to address this worldwide problem.

References

Footnotes

  • Contributors XH was responsible for the manuscript writing, data collection and data analysis. PYL, SK and MH did the major revision to the manuscript. MH was responsible for the concept of the study and study supervision.

  • Funding This study was supported by the WHO, Geneva, Switzerland (under National Institutes of Health, Bethesda, Maryland, USA, contract No. N01-EY-2103) and the by Fundamental Research Funds of the State Key Laboratory of Ophthalmology at the Zhongshan Ophthalmic Center. Professor He receives support from the University of Melbourne at Research Accelerator Program and the CERA Foundation. The Centre for Eye Research Australia receives Operational Infrastructure Support from the Victorian State Government. The sponsor or funding organisation had no role in the design or conduct of this research.

  • Competing interests None declared.

  • Ethics approval WHO Secretariat Committee on Research involving human subjects and Institutional Review Board at ZOC in Guangzhou, China.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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