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Review Article

Diabetic Retinopathy in the Asia-Pacific

Chua, Jacqueline BOptom, PhD*,†; Lim, Claire Xin Ying*,§; Wong, Tien Yin FRCS, PhD*,†,¶; Sabanayagam, Charumathi PhD*,‡,¶

Author Information
The Asia-Pacific Journal of Ophthalmology: January 2018 - Volume 7 - Issue 1 - p 3-16
doi: 10.22608/APO.2017511
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Abstract

Diabetes mellitus (DM) is a growing epidemic worldwide and the Asia-Pacific is expected to experience the greatest burden of DM, where economies are moving from low- to middle-income levels.1,2 In China, a large-scale population-based study conducted on 46,239 adults reported a 14-fold rise in DM prevalence over the span of 30 years (0.67% in 1980 vs 9.7% in 2008).3 The Asia-Pacific is home to half of the people with diabetes in the world; specifically, 153 million and 78 million are from the Western Pacific and Southeast Asia, respectively.4 Populous countries, such as China and India, have achieved recent exponential economic success, and in turn, adopted dramatic lifestyle changes such as unhealthy diets and a lack of physical activity leading to obesity, high blood pressure (BP), and high cholesterol contributing to the rising prevalence of diabetes.5

With increasing prevalence of DM, prevalence of diabetic retinopathy (DR), a leading cause of blindness in adults, is also set to increase.6 Vision impairment from DR places a considerable burden on patients' quality of life (QoL).7 Globally in 2015, an estimated 36 million were blind and 216 million people had visual impairment.8 The largest number of blind and visually impaired people resided in the Asian region, namely, South Asia, followed by East Asia and Southeast Asia.8 Diabetic retinopathy caused 1.1% of all cases of blindness and 1.3% of all visual impairment in 2015.9 The percentage of blindness caused by DR varied in the Asia-Pacific, ranging from less than 1% in South Asia (0.16%), Oceania (0.32%), East Asia (0.51%), and Southeast Asia (0.59%) to more than 3% in Central Asia (3.60%), high-income Asia-Pacific countries (3.87%), and Australasia (4.48%).10 Prevalence of blindness and visual impairment due to DR decreased between 1990 and 2015 in Oceania and Central and Eastern Europe, yet increased in the high-income Asia-Pacific, North America, Australasia, and Asian regions.9

Vision loss from DR is almost entirely preventable.11 In a meta-analysis that included 27,120 diabetic participants, the pooled incidence of proliferative diabetic retinopathy (PDR) was found to be lower in participants from 1986-2008 (2.6%) compared with participants from 1975-1985 (19.5%).12 These findings highlight the benefits of having programs targeted at increasing awareness of DR-related risk factors, earlier identification and initiation of care for patients with retinopathy, and improved primary interventions through glycemic and BP control. The main limitation of the meta-analysis, however, is a lack of contributing data from countries within the Asia-Pacific. With diabetes13 and DR rapidly increasing in the Asia-Pacific, it is vital to ensure that ophthalmologists are adequately prepared. In this review, we describe the DR-related epidemiology, its risk factors, screening strategies, management, and public health challenges faced uniquely within the Asia-Pacific.

EPIDEMIOLOGY

Prevalence of DR

Vision-threatening DR (VTDR) consists of the advanced stage of PDR or diabetic macular edema (DME).14,15Table 1 summarizes the prevalence of studies conducted within the last decade, organized by regions.16 A majority of prevalence studies from the Asia-Pacific focused on DR in type 2 diabetes because of the low prevalence of type 1 diabetes in these populations. Hence, comparison of DR prevalence between Asia-Pacific and global estimates14 will be restricted only to type 2 diabetes.

TABLE 1
TABLE 1:
Prevalence of Diabetic Retinopathy Among Diabetic Subjects From Studies Conducted in the Asia-Pacific
TABLE 1
TABLE 1:
Continued
TABLE 1
TABLE 1:
Continued

The prevalence of DR among type 2 diabetes from Singapore (30.4-35.0%),17-19 China (11.9-43.1%),20-25 Hong Kong (12.9-39.0%),26,27 Taiwan (25.0%),28 Pakistan (27.4%),29 Malaysia (39.8%),30 Sri Lanka (27.4%),31 Thailand (24.0-31.4%),32,33 and Australia (28.5-39.4%)34-36 is comparable to the United Kingdom37,38 and United States39 (28.5-39.1%). Studies from South Korea (15.8%),40 India (9.6-33.9%),41-50 and New Zealand (19.0-22.5%)51,52 revealed lower DR prevalence than Western countries, whereas Indonesia (43.1%)53 had significantly higher DR prevalence. The authors suggested that the low DR prevalence in South Korea40 may be a result of an effective diabetes program as evident by their high (80%) rates of diagnosed diabetes. The availability of good healthcare alone, however, cannot explain why Singapore has twice the prevalence of DR as compared with South Korea, as the healthcare systems in these countries are comparable in terms of their accessibility and proficiency. Moreover, Singapore also had high (89%) rates of diagnosed diabetes.17

Estimates on VTDR prevalence from Singapore (7.1-9.0%),17-19 China (4.4-13.8%),20-22 Hong Kong (9.8%),26 Nepal (14.4%),54 and Indonesia (26.3%)53 reported higher VTDR prevalence than the United Kingdom37,38 and the United States39 (1.4-4.4%). This implies that most DR cases may have been detected only when symptomatic or complications have occurred, or that these populations are genetically more susceptible to the severe form of DR. Countries such as South Korea (4.6%),40 Taiwan (2.8%),28 India (3.3-6.6%),42,46,50 Australia (non-Indigenous: 4.4%),34 and New Zealand (2.5%)52 reported similar VTDR prevalence as Western countries. Comparison of VTDR between Asia-Pacific and Western countries, however, should be interpreted with caution. A majority of the countries in the Asia-Pacific17-22,25,26,28,40,42,43,46,50,53 considered the severe form of nonproliferative DR (NPDR) as part of VTDR, whereas the global estimates only considered PDR and/or DME.14 Prevalence of DME in South Korea (2.8%),40 Singapore (5.7-7.2%),18,19 China (5.2-11.2%),21,25 Hong Kong (8.6%),26 Nepal (5.5%),55 Sri Lanka (5.3%),31 Australia (8.5%),35 and New Zealand (11.4%)51 is higher than the West (1.4-3.8%).38,39

Ethnic Differences

Studies from Australia36,56 and Singapore17,57 reported that the frequency of type 2 DM varied by race/ethnicity but the frequency of DR prevalence did not. Within Australia, although the prevalence of DM in indigenous populations was 8 times higher than non-Indigenous Australians, the prevalence of DR was essentially similar between Indigenous and non-Indigenous Australians.36,56 Similarly in Singapore, although the prevalence of DM among Indians (21.6%) was 2-fold higher compared with Chinese (11.5%), the prevalence of DR did not vary greatly between them (Indians 36.5% and Chinese 30.3%).17,57 Rather, the differences may be attributed to different racial and cultural attitudes that favor practices that are considered risk factors for DM, such as alcohol consumption, cardiovascular disease prevalence, smoking, obesity, and hypertension.2,58

Indians living in Singapore had a higher DR prevalence than Indians living in an urban region of India (18%).46 The authors speculated that the higher DR prevalence observed in Singapore Indians may be a result of an increased acculturation to a Westernized lifestyle.59 This hypothesis is in line with the increased prevalence of DM and DR among second-generation Indian immigrants than first-generation Indian immigrants living in Singapore. Furthermore, the lower prevalence of DR may be a result of selective mortality of those with DR in urban India, leading to a lower prevalence.

Urban-Rural Differences

Rapidly developing economies such as China and India are observing an urban-rural divide in terms of DR disease burden. In India, the less developed rural region demonstrated a marked lower prevalence of DR (10.3%42 vs 18.0%46) in the type 2 diabetes population. Similarly in China, the poorer southern regions experienced lower prevalence of DR and VTDR (27.6% and 11.9%) than the more affluent northern regions (33.1% and 15.5%).20 However, earlier studies from China (2008,60 2009,25 2011,61 2012,24 201523) consistently reported higher prevalence of DR among adults with type 2 diabetes living in rural regions (29.1-43.1%)24,25 compared with their urban counterparts (18.1%).24 One plausible explanation as suggested by the authors may be a lack of access to medical resources, resulting in higher rates of undiagnosed DM, which puts people living in the rural area at higher risk of developing severe forms of DR.20

MODIFIABLE RISK FACTORS

Table 2 summarizes the common modifiable risk factors for DR, namely, hyperglycemia, BP, dyslipidemia, and obesity, from studies conducted in the Asia-Pacific. Studies from the Asia-Pacific have reported consistent associations between hyperglycemia19,21,40,42,62-67 and systolic BP18,19,21,40,64-67 with DR but less consistent association with diastolic BP.18,40,42,65 Furthermore, conflicting findings have been reported between associations of lipid serum levels and obesity with DR.

TABLE 2
TABLE 2:
Modifiable Risk Factors of Diabetic Retinopathy in Cohort Studies Conducted in the Asia-Pacific
TABLE 2
TABLE 2:
Continued

Studies from China,62 South Korea,40 Singapore,18 and Australia68 did not find any significant associations between dyslipidemia with DR. However, a study from China found that a higher level of triglycerides was protective of DR [odds ratio (OR), 0.93; P = 0.01], whereas higher levels of low density lipoprotein (LDL) cholesterol were associated with DR (OR, 1.15; P < 0.001).21 Also, higher levels of total (and LDL) cholesterols were protective of any DR (P = 0.001) but not with VTDR among Singaporean Malays.19 In Australia, higher levels of total (and LDL) cholesterols were independently associated with clinically significant macular edema (CSME) but not with DR.68 The differential finding between low triglyceride21 (and cholesterol)19 levels with retinopathy remained unexplained and requires further exploration by other studies.

Asian studies reported either a nonsignificant or inverse association of body mass index (BMI) with DR. Studies from China21,69 reported no significance between BMI and DR, whereas those from South Korea40 and Singapore70-72 found an inverse relationship between BMI and the presence of DR.73 It is possible that lower BMI may reflect a more advanced, poorly controlled form of diabetes that results in both unintentional weight loss and DR, whereas those diabetics with higher BMI may have a shorter duration or milder stage of the disease that is less likely to cause DR. Another possible explanation for the protective effect of BMI could be that persons with DR could have adopted positive behavioral modifications that led to lower BMI levels. A study on Western individuals from Australia reported opposing results, where higher BMI was found to have increased the odds of having DR. A recent study from Singapore reported that, though a lower BMI was protective of DR, a higher waist-hip ratio (WHR), indicating abdominal obesity, was associated with an increase of DR in women.70 These findings suggest that WHR may be a more accurate indicator than BMI for monitoring for obesity in Asians.

A majority of Asia-Pacific studies have used an observational study design where temporality of diseases cannot be drawn. There is a need to assess the ethnic variations in DR risk factors using a longitudinal study design with uniform measurement methods to examine DR-related causal risk factors.

PREVENTION AND SCREENING

Controlling Risk Factors

Studies conducted in the Asia-Pacific region have supported a correlation between glycemic control and diabetes complications in type 2 diabetes patients.66,74,75 A clinical study from Australia showed that patients with poor BP or lipid control in addition to poor glucose control were at a greater risk of DR, compared with glucose control alone.74 In a recent clinical study from Singapore, a wider variability of systolic BP, even among those with good glycemic control, was associated with moderate DR among patients with type 2 diabetes.66 Good glycemic control is also important as it can lead to the regression of DR. In China, a 5-year community-based prospective study on patients with type 2 diabetes showed DR regression in 24% of patients (n = 110), which occurred mostly in patients with lower glucose and lower serum triglyceride levels.76 In Hong Kong, the regression rate was 13.2% and was also associated with lower glycated hemoglobin A1c (HbA1c) along with an absence of albuminuria.63

Data from the UK Prospective Diabetes Study and the Diabetes Control and Complications Trial, major clinical trial studies from the United Kingdom and United States involving white populations, showed that controlling blood glucose (HbA1c < 7%)77,78 and BP79,80 levels slowed the onset and progression of retinopathy. However, there is no clinical trial data from the Asia-Pacific. Thus, there is a need to have randomized controlled trials to test the benefit of lowering blood glucose and BP in populations within the Asia-Pacific.

Screening Methods

Regular photographic screening of DR is an effective strategy to prevent vision loss from DR.81 There were regional variations in the methods of DR screening used. In India, most patients were diagnosed with DR in eye hospitals,82 which often used DR screening camps, as opposed to programs integrated into existing diabetes management clinics. Despite these efforts, however, the coverage of screening services in India was still limited, with the majority of programs reaching less than half of their targeted districts.82 In Cambodia, the majority of patients with diabetes presented to the eye hospital as walk-in cases.83 In China, DR screening among persons with diabetes has not been carried out nor has a systematic screening program for DR been established.

The nonmydriatic camera is an acceptable screening tool, used in studies from developed countries.84 The popularity of nonmydriatic cameras has increased because of 3 reasons; first, its lack of dilation makes screening easier to perform without ophthalmologist supervision; second, it is considered a safer option, particularly in Asia, where acute angle closure is a concern; third, it is a much preferred method by patients who travel long distances to return home. One study in China reported a sensitivity of 67% and specificity of 94% of 1-field fundus photographs taken with a nonmydriatic camera when compared with ophthalmoscopy in detecting VTDR; whereas for detecting any DR, the sensitivity and specificity of the nonmydriatic camera were 76% and 80%, respectively.85 Another study in China, using 2-field fundus photographs, found sensitivity and specificity to be 86% and 92%, respectively, in detecting VTDR and 91% and 80% in detecting any DR, compared with single-field.85 These numbers are comparable to a meta-analysis of nonmydriatic cameras, which reported 70% sensitivity and 87% specificity for detecting any DR (n = 1960).86

A growing body of evidence has shown the efficacy of remote DR screening programs, proving that telemedicine is able to improve rates of DR screening for patients in remote areas with limited access to ophthalmology services. In Australia, the Remote Outreach DR Screening (RODRS) Service was implemented to provide appropriate DR screening for remote communities. The RODRS service was highly successful as screening rates increased 4-fold from 16.3% to 66.3%.87 In India a trial estimated that 150 patients could be screened per day with only 1 ophthalmologist making final diagnoses from a separate location.88 Alternative models such as the Aravind Eye Care System of India89 and the Peking University Eli Lilly Diabetic Eye Disease Centre in China are emerging models for long-term and sustainable management of DR in large developing countries, whereas initiatives such as the delivery of effective eye care in rural India via a mobile van have been used.2

Given the exponential rise of DM globally, the manpower needed for DR screenings is likely to be outpaced. A study from Singapore demonstrated that trained nonphysician graders are able to provide good detection of DR and maculopathy (κ = 0.66) from fundus photographs.90 Recent studies from the United States91 and Singapore92 showed that automated detection of DR lesions from fundus photographs using deep-learning algorithms had high sensitivity and specificity for identifying DR using retinal images. Hence, software for automated detection of DR lesions from fundus photographs can reduce the workload for manual grading considerably by filtering out healthy eyes and identifying DR lesions to aid in quicker diagnosis and reduce human error. Digital retinal imaging screening on a telemedicine platform using an automated detection system may be a feasible and cost-effective public healthcare strategy for the surveillance and prevention of blindness due to DR in low-middle income countries in view of the lack of resources.

DR Screening Guidelines in the Asia-Pacific

Only less than a quarter of countries in the Asia-Pacific have nationally available DR screening guidelines. Of these, 5 countries, namely, Australia,93 New Zealand,94 China,95 India,96 and Malaysia,97 have guidelines written specifically on the care of DR, whereas the remaining 5 countries (Japan,98 Singapore,99 Hong Kong,100 the Philippines,101 and Sri Lanka102) incorporated their DR screening guidelines within diabetes guidelines. A recent systematic review of DR screening guidelines in Asia reported that most of these countries were in line with the International Council of Ophthalmology's standards on the time to commence initial DR screening and frequency of follow-up evaluations.103 However, guidelines are vague on the threshold for referrals to specialists based on disease severity as most are based on visual acuity. A situational analysis from India found that a significant portion of programs still refer patients to eye specialists for early DR.82 Although the effect of this practice has not been assessed, the current standards of practice recommend referring only VTDR to specialists and monitoring for other DR. A simple and more user-friendly standardized classification guideline would allow for better communication between ophthalmologists and primary care professionals.104

Effectiveness of any screening program depends on the adherence to the guidelines set. In Australia, a study found 77% of non-Indigenous Australians adhere to the screening guidelines compared with only 53% of Indigenous Australians.105 The examination rates among developing countries are considerably lower. Less than one third of diabetic patients from India106 and China107 had undergone an eye examination in the previous year. In South Korea, only a third of patients underwent an annual dilated fundus examination on a regular basis.108 Data from rural China suggest that use of eye care among those with diabetes may even be lower.25 Also, resource constraints in developing regions of the Asia-Pacific may be limited to the provision of screening services and lack the continuity of screening for DR, which is crucial for the management of diabetes-related complications.103

MANAGEMENT

Management of DR in low-middle income countries faces major challenges due to lack of access to eye specialists, health care resources, and facilities. In India, 72% of the population live in rural areas, whereas the majority of ophthalmologists are based in urban centers.109 Hence, people living in remote and underserved areas may experience greater challenges in accessing specialized expert eye care. Even though the use of retinal photocoagulation has been the mainstay of DR treatment for the past few decades, a 2000 national survey in China showed that 90% of rural hospitals had no laser facilities.110 This may explain the finding from the Handan Eye Study, where less than 10% of patients in rural China requiring laser treatment for diabetic eye disease had received it.25 In Cambodia, a situational analysis on DR management reported a lack of optical coherence tomography and vitreoretinal operating machines in the eye hospital.83

Treatment Options

Newer pharmacological developments have revolutionized DR treatment from vision stabilization to vision improvement.15 Xu et al111 reported good clinical efficacy using intravitreal ranibizumab and conbercept in 62 Chinese patients over a 12-month clinical study. Sato el al112 did a retrospective review of 56 eyes of Japanese patients with DME treated with intravitreal ranibizumab and reported predictors of good clinical outcomes included better baseline best corrected visual acuity and lower central retinal thickness; hence, this supports the early use of intravitreal anti-vascular endothelial growth factor (anti-VEGF) in DME. However, the high cost of treatment, travelling time, and lack of reimbursed healthcare may impair patient compliance; hence, the number of anti-VEGF injections might be suboptimal.113 Also, many patients in both developed and developing countries do not have sufficient resources to cover the long-term treatment costs for DME.114 As such, ophthalmologists in the Asian regions often select focal/grid laser photocoagulation as their mainstay of treatment and patients are only treated when DR has progressed to advanced stages.

IMPACT OF DIABETIC RETINOPATHY

Economic Impact

Few studies in the Asia-Pacific have reported the cost of illness associated with DR. A large-scale longitudinal study in Taiwan reported increased healthcare costs associated with progressive DR.115 Specifically, individuals who progressed from early to advanced stages of DR experienced the greatest increase in cost compared with patients without progression, from US$2723 in 2000 to US$6204 in 2004.115 In Singapore, a study on 500 patients with type 2 diabetes found that in 2010, the annual direct medical cost associated with diabetes care was US$1575 per patient.116 They found that medications and presence of diabetes-related systemic complications were significantly associated with cost.116 In a recent study in Singapore, the presence and severity of DR were associated with increased direct medical costs in patients with type 2 diabetes, which suggested that preventing progression of DR may reduce the economic burden of DR.117 However, in the earlier study, the presence of DR was not a strong determinant of costs.116 As suggested by the authors, a possible reason is that the cost data were obtained from primary clinics,116 where conditions were less severe compared with those patients visiting a secondary hospital.117 This may have limited the analysis on the influence of DR on cost.

Systematic DR screening was cost-effective compared with opportunistic screening for DR. Rachapelle and co-workers118 examined the cost-effectiveness of the Sankara Nethralaya Medical Research Foundation telemedicine DR screening program in rural southern India. They found the program to be cost-effective at a frequency of screening for up to 2 years.118 However, yearly DR screening was no longer considered as cost-effective (defined as less than US$3183 per quality-adjusted life year gained). Furthermore, once household costs were included in the model, only screening once every 5 years was considered cost-effective. In Singapore, a cost-effectiveness analysis was performed for a telemedicine-based DR screening program, which calculated the total cost savings to be US$128 per person.119 Upon extrapolation to the large diabetic population in Singapore, its future cost savings to the healthcare system was projected to be US$21 million.119 In Japan, implementation of a DR screening program would result in an incremental cost of US$64 and estimates a significant reduction (-16%) in cases of adult blindness.120 However, costs varied depending on the capabilities of healthcare systems; hence, countries should evaluate strategies to make screening programs as sustainable and cost-effective as possible.

Patient Outcomes

Visual impairment as a result of DR has a significant negative impact on the patient's QoL. In Singapore, a population-based study showed that VTDR and PDR are the DR severity levels at which functioning is compromised in Malay persons with diabetes.121 In addition, the 3 most difficult vision-dependent activities for people with DR were associated with reading small print, completing lottery forms, and reading newspapers, whereas the 3 least difficult activities were cooking, playing cards, or seeing stairs.121 In a clinical study from Australia, poor visual acuity from DR in the better eye was associated with decreased functioning and emotional well-being in patients with DR.122 In a recent study from Australia on patients with DR and DME, poorer self-reported vision in adults with DR was associated with emotional distress through limitations in daily living activities and social factors.123 Others have shown that there was a significant improvement in Japanese patients' quality of life after vitreous surgery for PDR even without significant corresponding improvements in visual acuity.124 These findings clearly demonstrate that the presence and severity of DR and vision impairment associated with DR are detrimental to patient functioning and QoL. However, such patient-centered research is absent from populous countries like India and China, which are expected to experience the greatest burden of DR.13

PUBLIC HEALTH CHALLENGES AND FUTURE DIRECTIONS

Patient Awareness

Patient awareness is alarmingly low and is significantly associated with poor health literacy, low socioeconomic status, and poor control of HbA1c and BP levels.1 Awareness of eye-related complications in the diabetic population varied, ranging from 28.8% to 84%, whereas specific knowledge about DR was less likely to be reported.125 For example in India, 45% of people with diabetes only accessed eye clinics after losing their vision.82 In South India, a study reported that only 1 in 10 people in the community are aware that DR is a possible sequela of diabetes.126 Also, 72% of informational sheets on diabetes in Indian clinics did not contain any mention of DR.125 In China, even among diabetic subjects who reported recent eye examinations, nearly half believed that regular eye examinations are unnecessary in the absence of visual symptoms.107 A similar misconception was reported in Myanmar, which showed that despite 92% of diabetic individuals being aware that they should visit an ophthalmologist, 34% felt the need to see an ophthalmologist only when they developed trouble with their eyesight.127

More targeted health education towards people with lower educational levels and socioeconomic status could potentially cover gaps in health knowledge and primary care physicians could closely monitor and counsel those with poorly controlled HbA1c and BP levels. Another recommendation would be to train health professionals to engage with newly diagnosed diabetic patients in discussions about diabetes control and management along with its complications, specifically potential blindness.128

Poor Control of Risk Factors

A major effort in DR prevention comes from optimizing diabetes care to reduce onset of DR. Optimal glycemic control varied among patients with DR, ranging from 17% in Singapore75 and 20% in India129 to 69% in Australia.74 Findings from these few Asia-Pacific74,75,129 studies demonstrate a poorer glycemic control among Asians than Australians. A number of interventional studies have been tested and demonstrated to improve diabetes self-management. These limited studies, namely, from South Korea,130 China,131-133 Malaysia,134 and India,135,136 found positive impacts on patients' glycemic control or positive behavioral change (eg, diet, exercise, self-monitoring of blood glucose). However, the small number of studies limits inferences about the Asia-Pacific population.137 More research is needed to evaluate the benefits of low-cost screening tools, along with the efficacy, cost-effectiveness, and sustainability of culturally appropriate interventions in such countries.

Scarce Data on Low-Middle Income Countries

We can only tackle DR-related visual impairment if we are able to see the full picture. As seen in Table 1, there remain countries without DR prevalence data, namely, Afghanistan, Brunei Darussalam, Bhutan, Cambodia, Lao People's Democratic Republic, Maldives, Myanmar, Philippines, Vietnam, countries within the central region of Asia (ie, Armenia, Azerbaijan, Georgia, Kazakhstan, Kyrgyzstan, Mongolia, Tajikistan, Turkmenistan, and Uzbekistan), and also countries within the Oceania region (ie, Kiribati, Marshall Islands, Micronesia, Papua New Guinea, Samoa, Tonga), where diabetes seems to be increasing rapidly.

Despite being the most common cause of DR-induced vision loss, even fewer countries in the Asia-Pacific region have provided DME data. For example, countries such as Taiwan, Bangladesh, India, Pakistan, Indonesia, Malaysia, Thailand, East Timor, and those in Oceania have mostly reported prevalence of VTDR or CSME but not specifically DME. Overall, epidemiological data on type 1 data and DME prevalence are relatively scarce.

Epidemiological studies of DR in low-income countries in the Asia-Pacific may be hindered by a lack of resources. The Rapid Assessment of Avoidable Blindness (RAAB) screening method may be adapted for monitoring DR prevalence in resource challenged areas such as developing countries of the Asia-Pacific.138-141 By minimizing the sample size and only screening high-risk individuals, RAAB+DR reduces screening costs while gathering fairly accurate prevalence estimates rapidly. Considering that there is inadequate data on DR prevalence in certain developing countries, RAAB+DR may be suitable for the collection of good quality epidemiological data, which is essential for planning and implementation of future public health policies.125

Adherence and Barriers to DR Screening

Adherence to screening has been hindered by lack of awareness of DR, lack of healthcare resources, and lack of accessibility.1 Despite high prevalence of diabetes and its complications, awareness of DR is low. This occurs with equal predilection in both developed and developing countries.1 Studies from China107 (n = 824) and Indonesia142 (n = 196) showed that diabetic patients with a better DR knowledge score tended to attend regular eye examinations. In rural China, a focus group study found that the top 3 patient-identified barriers to screening were forgetting appointments, feeling that physicians were not well-trained, and transportation costs.143 Medical cost, however, was not ranked as a major barrier to accessing eye care, which was in accordance with another study from China.107 However, in India, a clinical study on 233 patients with VTDR seen at tertiary referral center cited financial cost as the major reason for noncompliance with follow-up appointments.144 Country-specific barriers such as high costs, travelling time, inconvenience from screening or treatment, and lack of medical reimbursements may impede patient uptake.125,128

CONCLUSIONS

As this review shows, DR remains a significant major public health issue in the Asia-Pacific. A major concern is the more severe problem of VTDR, which could be a reflection of the lack of routine DR screening and timely treatment in the developing region, resulting in its late diagnosis only at the symptomatic stage. Awareness of DR remains alarmingly low and well-organized efforts are needed to educate patients, physicians, and policy makers. Use of low-cost screening technologies such as digital retinal imaging and remote grading may identify patients requiring ophthalmologist review. Telemedicine has increased access to screening for diabetics living in remote and hard-to-reach areas and has optimized screenings to be more cost-efficient and convenient in urban areas. Uptake of anti-VEGF therapy for treatment of DR is sluggish due to cost. A more cost-effective treatment strategy for DME is urgently needed for the Asia-Pacific. Management of DR in the Asia-Pacific requires establishing clear, specific guidelines that would serve as a foundation for structuring an effective public healthcare program.

A limitation of this review is the inclusion of English-only studies. Ideally, reviews should have included all studies conducted on the topic regardless of language. Even though this was applied for practical reasons, it means that a large number of relevant papers may have been excluded, especially as English is not the primary spoken language in most developing countries. Further research and initiatives to obtain prevalence data on DR and conduct randomized clinical trials for the Asia-Pacific are needed, which can further reduce the burden of blindness because of DR.

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      Keywords:

      diabetic retinopathy; Asia-Pacific

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