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Abstract
Aims To evaluate the prevalence of myopic maculopathy among participants aged 50 years and older in rural southern China.
Methods Population-based, cross-sectional study. Subjects were recruited using cluster sampling from Yangxi County, Guangdong Province, China from August to November in 2014. Non-cycloplegic autorefraction and fundus photography were performed on all of the participants. Myopic maculopathy was graded based on fundus photographs using the International Classification of Myopic Maculopathy.
Results Among 5825 individuals who participated (90.7% response rate), a total of 4469 participants with gradable fundus photographs for myopic maculopathy and automated refractive data were included in this study. The mean age of these participants was 65.50±9.70 years. The crude prevalence of myopic maculopathy was 1.4% (62/4469; 95% confidence interval [CI] 1.0% to 1.8 %) and age-standardised prevalence was 1.2% (95% CI 1.1% to 1.2%). Diffuse chorioretinal atrophy, patchy chorioretinal atrophy, macular atrophy, lacquer cracks and staphyloma were observed in 43 (1.0%), 3 (0.1%), 1 (0.1%), 15 (0.3%) and 8 eyes (0.2%), respectively. Myopic maculopathy was more common in eyes of older participants (OR 1.07; 95% CI 1.03 to 1.11) and more myopic spherical equivalence (OR 1.69; 95% CI 1.57 to 1.84).
Conclusion The prevalence of myopic maculopathy was low among the rural southern Chinese population. Diffuse chorioretinal atrophy was the most common retinal finding among Chinese myopes.
- prevalence
- risk factors
- myopic maculopathy
- rural China
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Introduction
It has been estimated that the rate of myopia may be as high as 80% in certain regions of East Asia, which is an important public health concern.1 2 Myopia can be managed through the use of corrective frame glasses and contact lens, or corrected through various intraocular or laser refractive surgeries, usually with good visual acuity outcomes. Despite these advancements in technology that enable myopes to achieve excellent corrected visual acuities, myopic maculopathy might occur in 32.2% of myopic participants,3 which is a condition that may cause sight-threatening complications to arise in patients with myopia. This is particularly prevalent among high myopes, which is defined as a spherical power of ≤−6.0 dioptres (D).
Myopic maculopathy mainly presents in the posterior portion of the eye as a result of the stretching of the posterior portion accompanied with axial elongation, including diffuse chorioretinal atrophy, patchy chorioretinal atrophy, macular atrophy, lacquer cracks, Fuchs’ spot, choroidal neovascularisation and staphyloma. It has been reported that myopic maculopathy is the second leading cause of visual impairment and blindness among Chinese adults aged over 40 and the third leading cause of bilateral low visual acuity among Japanese adults aged over 40.4–6
Despite numerous studies highlighting the complications associated with myopic maculopathy, its prevalence and associated factors were not fully documented, especially for the population of China. Previous studies conducted within a Chinese population are dated from almost 10 years ago, necessitating an urgent literature update. Thus, our study aims to explore the prevalence of myopic maculopathy and its associated factors in rural southern China.
Method
Study population
The Yangxi Eye Study is a population-based, cross-sectional study of Chinese aged over 50 in rural southern China. It is an expanded part of the China Nine Province Survey in 2014, a national population-based study aiming to explore the conditions of visual impairment and blindness in individuals aged over 50 in rural China.7 Yangxi was a rural county in western Guandong Province with an estimation of population of 513 802 in 2012. Yangxi district was selected for its representative of rural area in Guangdong. Using the data from the Residence Administrative Committee, clusters of about 1000 individuals which contained approximately 20% of ones aged ≥50 years was constructed geographically for the sampling frame. The details of the sampling frame and methods were described elsewhere.8 The Yangxi Eye Study was implemented from August to November 2014. A total of 6425 eligible individuals were using the sampling frame of cluster random sampling from 268 geographically defined basic sampling clusters based on the Residence Administrative Committee data. Eligible individuals were defined as participants aged ≥50 years who had been living in the selected areas for ≥6 months.
Examinations
Door-to-door visits were carried out by the recruitment team and a standard questionnaire was used by trained experienced interviewers to collect the following information from participants: general medical history, current medication usage, history of ophthalmic disorders and education level. For education level, trained and experienced interviewers asked each participant their highest level of education attained (selecting from Uneducated, <Primary School, Primary School, Junior Middle School, High School, College or higher in the form). Systemic examinations including blood pressure, height and weight were also acquired according to the standardised protocol.
Eye examinations including non-cycloplegic automated refraction (KR-8900; Topcon, Tokyo, Japan), slit-lamp biomicroscopy, direct ophthalmoscopy and mydriatic fundus photography using a digital fundus camera (FundusVue; Crystalvue, Taoyuan City, Taiwan) were performed by ophthalmologists for all participants according to a standardised protocol. Pupil dilation was achieved with compound tropicamide eye drops three times for every eye, containing 5 mg tropicamide and 5 mg phenylephrine hydrochloride in each millilitre.
Visual acuity was evaluated using ETDRS charts.9 Presenting visual acuity (PVA) of each eye by habitual correction was also recorded, and best-corrected visual acuity (BCVA) was acquired after pupil dilation in participants with PVA of <20/40 in either eye.
Definitions and myopic maculopathy grading
Myopia was defined as less than −0.5 D and high myopia as equal to or less than −6.0 D. Retinal photographs were obtained after mydriasis, one centred on the fovea and the other one centred on the optic disc. Myopic maculopathy was graded among myopic participants using the International Photographic Classification and Grading System for Myopic Maculopathy.10 In brief, myopic maculopathy was classified into five categories based on its severity: no myopic retinal degenerative lesion—category 0 (C0); tessellated fundus only—category 1 (C1); diffuse chorioretinal atrophy—category 2 (C2); patchy chorioretinal atrophy—category 3 (C3); macular atrophy—category 4 (C4). Additional lesions including lacquer cracks (LCs), Fuch’s spot and myopic choroidal neovascularisation, that is, ‘plus’ lesions, were also recorded. The above described classification system of myopic maculopathy did not include posterior staphyloma, but classified it separately into seven categories including wide, narrow and inferior macula involved staphyloma, nasal, peripapillary, inferior macula not involved staphyloma and other types of staphyloma. The presence of myopic maculopathy was defined as C2 or greater, and/or any additional lesions, and/or staphyloma.
To evaluate the interobserver agreement of two experienced ophthalmologists (ZL, RL), a test set with 60 images from 60 participants with high myopia (40 had C2 or greater myopic maculopathy) was used to test the ophthalmologists. The unweighted kappa was 0.81 for C0/C1, 0.77 for C2, 0.83 for C3, 0.85 for C4, 0.69 for LC, 0.67 for Fuch’s spot and 0.71 for staphyloma. The two ophthalmologists interpreted each retinal photograph independently using the above-described criteria. In the case of any discrepancy, the images were evaluated by the third specialist (MH) for final decision.
Statistical analysis
Only participants with gradable fundus photographs for myopic maculopathy and automated refractive data were included in this study. The overall prevalence of myopic maculopathy with 95% confidence intervals (CIs) were evaluated. Age-specific and gender-specific prevalence of each lesion of myopic maculopathy was also calculated. Spherical equivalent (SE) was calculated as spherical refraction plus 1/2 of cylindrical power. Myopic maculopathy was analysed based on the worse-affected eye for every participant. Pearson χ2 tests and Mann-Whitney U test were adopted to compare the characteristics between those participants with and without myopic maculopathy. Univariate and multiple logistic regression were adopted to evaluated risk factors for the presence of myopic maculopathy. Odds ratios (ORs) with 95% CIs were calculated. Due to the design of random cluster sampling, cluster was adjusted in the analyses of prevalence and logistic regression. Visual impairment was classified into moderate (Snellen: 1/10–3/10, decimal: 0.1–0.3), severe (Snellen: 1/20–1/10, decimal: 0.05–0.1) and blindness (Snellen: <1/20, decimal: <0.05) (http://apps.who.int/classifications/icd10/browse/2015/en#/H54). The influence of myopic maculopathy on visual acuity was also evaluated between participants with myopic maculopathy and without these disorders using Pearson χ2 tests. All analyses were conducted using Stata V.14.0 software (StataCorp, College Station, Texas, USA). A p value<0.05 was regarded as statistically significant.
Results
The workflow of participants’ inclusion and exclusion is shown in figure 1. A total of 6425 participants aged 50 years and older were eligible and 5825 (90.7%) agreed to take part in this current study. Of these participants, 4526 (77.7%) had binocular fundus photographs, 362 (6.2%) had monocular fundus photographs and 937 (16.1%) had no fundus images or fundus images with poor quality for grading. Thus, 4888 (83.9%) had gradable fundus photographs. Among these participants, 4469 (91.4%) had automated refraction data. Finally, a total of 4469 participants (76.7%) were included in this study. The mean age was 65.50±9.70 years. There were 2239 men (50.1%) and 2230 women (49.9%).
Workflow of participants inclusion and exclusion for myopic maculopathy in the Yangxi Eye Study.
The prevalence of myopia and high myopia were 19.0% (848/4469; 95% CI 17.8% to 20.2%) and 1.3% (57/4469; 95% CI 1.0% to 1.6%), respectively. The prevalence of myopic maculopathy was 1.4% (62/4469; 95% CI 1.0% to 1.8%) with an age-standardised prevalence of 1.2% (95% CI 1.1% to 1.2%), and the rate of myopic maculopathy among myopic participants was 7.3% (62/848; 95% CI 5.7% to 9.3%). A total of 70 myopic maculopathy lesions were identified in 62 eyes, including diffuse chorioretinal atrophy (n=43), patchy chorioretinal atrophy (n=3), macular atrophy (n=1), lacquer cracks (n=15) and staphyloma (n=8). The staphyloma types included narrow macula involvement (n=4, 50%), wide macula involvement (n=3, 37.5%) and peripapillary staphyloma (n=1, 12.5%). The age-specific and gender-specific prevalence of myopic maculopathy lesion are summarised in table 1.
Age-specific and gender-specific prevalence of myopic maculopathy lesions
The characteristics of eyes with or without myopic maculopathy (clinical significant myopic maculopathy) are shown in table 2. Subjects with myopic maculopathy were older (71.80±10.64 years vs 65.40±9.65, p<0.001) and had more myopic SE (−6.84±5.74 D vs −0.03±1.73 D, p<0.001) than those without myopic maculopathy. There was no statistically significant difference attributable to gender (p=0.299), education level (p=0.131), systolic blood pressure (p=0.598) and diastolic blood pressure (p=0.072) between participants with myopic maculopathy and those without myopic maculopathy.
Characteristics of eyes with and without myopic maculopathy
The univariate logistic regression model demonstrated that older age (OR 1.07; 95% CI 1.04 to 1.09) and myopic SE (OR 1.69; 95% CI 1.55 to 1.83) were significantly associated with myopic maculopathy (table 3). Gender, education level, systolic blood pressure and diastolic blood pressure did not correlate with the presence of myopic maculopathy. The multiple logistic regression model showed that older age (OR 1.07; 95% CI 1.03 to 1.11) and myopic SE (OR 1.69; 95% CI 1.57 to 1.84) were significantly associated with myopic maculopathy.
Univariate and multiple logistic regression analysis of risk factors associated with myopic maculopathy
Table 4 explores the impact of myopic maculopathy on visual impairment and blindness. Among 62 participants with myopic maculopathy, only 12 participants (19.4%) showed normal vision for presenting visual acuity; the rest (n=50, 80.6%) had visual impairment or blindness, including 32 participants (51.6%) who had moderate visual impairment, 10 (16.1%) had severe visual impairment and 8 (12.9%) had blindness. Of the 50 participants with visual impairment and blindness, 36 (72.0%) could be corrected to normal vision and 14 (28.0%) had uncorrectable visual impairment.
Influence of myopic maculopathy on visual impairment and blindness
Table 5 shows a comparison of the literature regarding the prevalence of myopic maculopathy among different studies. Using the Chinese population from 2015 China Census as the standard (http://data.stats.gov.cn/search.htm?s=%E4%BA%BA%E5%8F%A3), age-standardised prevalence for all of these studies were calculated. The total prevalence of myopic maculopathy was similar with that reported in the Handan Eye Study, the Hisayama Study and the Blue Mountain Eye Study.11–13 Furthermore, it was lower than that in the Beijing Eye Study and the Shipai Eye Study.14 15
Comparison of prevalence of myopic maculopathy in different studies
Discussion
This population-based study reported on the prevalence of myopic maculopathy in rural China and showed that the crude and age-standardised prevalence of myopic maculopathy were 1.4% (95% CI 1.0% to 1.8%) and 1.2% (95% CI 1.1% to 1.2%), respectively. Subjects with older age and myopic SE were more likely to have the presence of myopic maculopathy. This southern rural Chinese population had a lower prevalence of myopic maculopathy compared with previous findings in an urban Chinese population of Beijing and Taiwan.10,14
The prevalence of our study was comparable with previous literature, such as that of the Handan Eye study, the Hisayama Study and the Blue Mountain Eye Study, which studied the rural Chinese population, the southern Japanese population and the white Australian population, respectively.6,12,13 In contrast, the Beijing Eye Study from Beijing city and Shipai Eye Study from Taiwan reported a prevalence of 3.1% and 4.2%, respectively. The study population of both studies above were Chinese urban dwellers, where there is a higher proportion of myopic or high myopic participants, and a correspondingly higher proportion of myopic maculopathy.16,17 In addition, the definition of myopic maculopathy among different studies were not consistent. The combination of these two important factors may contribute to the relative lower prevalence of this current study.
As in previous studies,13 14 18 the results from our study showed that a higher prevalence of myopic maculopathy was correlated with older age and more myopic SE. Ageing is an important factor that impacts on the pathological changes among participants with myopic maculopathy. Studies have revealed that increasing maculopathy severity was associated with increasing refractive error as well as older age.19 20
It has been demonstrated that myopic maculopathy was the leading cause of bilateral visual impairment and blindness.4–6 16 21–24 Our study supported this link between myopic maculopathy and visual impairment and blindness, with 80.6% (50/62) of participants with myopic maculopathy having a PVA classified as visual impairment or blindness. Fortunately, 36 of 50 participants (72.0%) could be corrected to normal vision, leaving 28.0% (14/50) of participants with myopic maculopathy with a BCVA classified as BCVA-defined impairment or blindness.
Strengths of this study include large sample size, the use of a newly developed standardised protocol of International Photographic Classification and Grading System for Myopic Maculopathy and analysis of the influence of myopic maculopathy on visual impairment blindness. However, potential limitations of this study should be noted. First, the participation rate of this study was 76.7% (4469/5825), which is acceptable and this rate is comparable with other aged population studies.11 13 The included participants that had the automated refraction data and gradable fundus photographs for myopic maculopathy were younger than non-participants (65.50 ± 9.70 years vs 69.71±11.67 years; p<0.001). Even though the difference was small, the low participation rate may introduce selection bias, which could lead to an overestimation or underestimation of the prevalence of myopic maculopathy. Second, the fundus photographs used to grade myopic maculopathy were non-stereoscopic, which may lead to an underestimation of staphyloma. Thirdly, other factors such as genetic factors were not collected in this study. Thus, we could not estimate the influence of these factors on the prevalence of myopic maculopathy. Finally, the collection of education level was not measured with reliability and validity. Even though trained and experienced interviewers asked each participant their highest level of education, there might still have some biases.
In summary, this current study documented the crude and age-standardised prevalence of myopic maculopathy in a southern rural Chinese population. The prevalence myopic maculopathy was lower than that in the Beijing Eye Study and the Shipai Eye Study but was similar to that in the Handan Eye Study, the Hisayama Study and the Blue Mountain Eye Study.
Acknowledgments
The authors thank ORBIS International North Asia for supporting the work.
References
Footnotes
ZL and RL contributed equally.
Contributors MH, JZ, XX and LA were involved in the concept, design and conduct of the study. ZL, RL, GJ, JH, XD and WX contributed to the acquisition and analysis. ZL wrote the paper. All authors revised and edited the manuscript.
Funding This work was supported by the National Institute of Hospital Administration, the Chinese National Health and Family Planning Commission and ORBIS International. MH receives support from the Fundamental Research Funds of the State Key Laboratory in Ophthalmology, Science and Technology Planning Project of Guangdong Province 2013B20400003, and the University of Melbourne Research Accelerator Program and the CERA Foundation. The Centre for Eye Research Australia receives Operational Infrastructure Support from the Victorian State Government.
Competing interests None declared.
Patient consent for publication Obtained.
Ethics approval This study was approved by the Zhongshan Ophthalmic Center Institutional Review Board and adhered to the tenets of the Declaration of Helsinki.
Provenance and peer review Not commissioned; externally peer reviewed.
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