Study on diabetic retinopathy in local elderly population

K L Chua 蔡金陵, K S Ho 何建生, K W Kwong 鄺家驊, W M Chan 陳慧敏

HK Pract 2003;25:603-610

Summary

Objective: To study the prevalence of diabetes mellitus retinopathy (DMR) among local elderly diabetics in a primary care setting and to determine the risk factors associated with the development of DMR.

Design: Community-based cross-sectional study.

Subjects: 463 diabetic patients aged 65 and above, who had undergone retinal photography at two local elderly health centres in the year 1999-2000.

Main outcome measures: The prevalence of DMR was examined in subjects newly diagnosed to have diabetes mellitus (DM) and in subjects previously diagnosed with DM. Risk factors analysis of DMR was also performed.

Results: A total of 463 elderly diabetic patients had taken retinal photography. Their age varied from 65 to 87 with a mean of 71. DMR was found in 21.5% of those with a known history of DM and in 7.7% of those newly diagnosed to have DM by routine health assessment. Higher HbA1c level and longer duration of DM were found to be associated with DMR.

Conclusion: Diabetic retinopathy is an important and common complication of DM. HbA1c level and duration of DM are associated with the development of DMR. Retinal photography is an effective screening programme that can be performed in a community based clinic.

Keywords: Diabetic retinopathy, retinal photography, risk factor analysis, elderly diabetics and community based setting.

摘要

目的： 研究本地接受基層護理的年長糖尿病患者，糖尿病視網膜病變（DMR）的患病率，並確定有關的危險因素。

設計： 社區為基礎的橫向性調查。

研究對象： 463位65歲及以上，於1999-2000年度，曾在兩所長者健康中心內接受視網膜攝影術檢驗的糖尿病患者。

主要測量內容： 分別調查新確診和已知的糖尿病患者的DMR的患行率，並分析DMR的危險因素。

結果： 463位年長的糖尿病患者接受了視網膜攝影術檢驗。 他們的年齡介乎65至87歲，平均年齡為71歲。在已知的糖尿病患者中，21.5%發現有DMR； 在新近診斷的糖尿病患者中，7.7%的病人在例行健康評估時，發現有DMR。 較高的糖化血紅蛋白水平和較長的糖尿病患時間與DMR有關連。

結論： 糖尿病視網膜病變是重要和普遍的糖尿病併發症。糖化血紅蛋白水平和糖尿病患者時間與DMR的形成有相關性。視網膜攝影術既可以似為有效的篩選方法，而又可在社區診所內進行。

詞彙： 糖尿病視網膜病變，視網膜攝影術，危險因素分析，年長的糖尿病患者，社區為基礎的機構。

Introduction

Diabetes Mellitus (DM) is becoming an epidemic in the Asia-Pacific region. Hong Kong is not immune to this problem and the situation is even worse among the elderly population. The local prevalence of diabetes is estimated to be around 7-8%.¹ However, among the local elderly people (age 65-74), the prevalence increases to 21.7% and 29.3% for male and female respectively.²

It is well known that DM can cause many complications e.g. retinopathy, nephropathy, neuropathy, coronary heart disease and stroke. Diabetes mellitus retinopathy (DMR) is estimated to be the most frequent cause of new cases of blindness among adults aged 20-74.³ In overseas studies, up to 21% of patients with type 2 diabetes have been found to have retinopathy at the time of first diagnosis, and more than 60% will have some degree of retinopathy after 20 years of diabetes.³ The prevalence varies in different diabetic populations. In the Barbados study, it was reported that 28.5% of the black diabetic population had DMR.⁴ The rate could be as high as 48% among the Hispanic community.⁵ In Singapore, Lau et al reported a prevalence of 21.8% among 13,296 DM patients.⁶ Local studies in Hong Kong reported a prevalence of 15-23%.^7-9 However, there is no study on the prevalence of DMR in the local elderly population.

The Diabetic Retinopathy Study (DRS) showed that panretinal photocoagulation surgery would significantly reduce the risk of visual loss from proliferative diabetic retinopathy, especially those with high-risk characteristics.¹⁰ It might reduce blindness in up to 50% or more of the cases. The Early Treatment Diabetic Retinopathy Study (ETDRS) established the benefit of focal laser photocoagulation surgery in eyes with macular oedema, particularly in those with clinically significant macular oedema.¹¹ Therefore, screening for DMR can substantially reduce the risk for visual impairment and blindness due to diabetes.¹²

Many clinical guidelines recommend annual screening for DMR.^13-15 The traditional way of detecting DMR in a primary care clinic is by direct ophthalmoscopy. However, this requires considerable skill of the doctors and motivation for patients to attend an examination. As a result, many diabetics may not be receiving an annual fundal examination as recommended. In addition, direct ophthalmoscopy by primary care doctors has the inherent problem of having a low sensitivity in detecting DMR: 22-56% in an UK study¹⁶ and 55% in a local study.⁸

Retinal photography has been found to be a better way for DMR screening than direct ophthalmoscopy. Its sensitivity ranges from around 65-90% and specificity from 85-90%. Repeated trials have confirmed its superiority over direct ophthalmoscopy.^7,8,16,17 Results of studies on assessing primary care doctors' ability in interpreting retinal photos have also been encouraging.^16-18 Therefore, in this study retinal photography was selected as the screening tool for DMR.

Methods

Eighteen elderly health centres were established by the Department of Health in 1998 to provide comprehensive health maintenance service for the elderly population in Hong Kong. All elderly persons aged 65 or above were eligible to enroll as members. Each client received a comprehensive annual health assessment with laboratory investigations including blood glucose. American Diabetic Association criteria were used to diagnose diabetes mellitus. Retinal cameras were available in only two elderly health centres at the time of study. All known or newly diagnosed diabetic patients were invited to have retinal photography with informed consent. Patients with a history of glaucoma were excluded from the study. Retinal cameras of the model Canon CR45NM were used at both centres and were operated by trained nurses. Single field 45 degree photos were taken through dilated pupils. These photos were then assessed by two experienced family physicians who had received formal training in the interpretation of retinal photos taking turns to read the photos. When there was doubt about the interpretation of any abnormalities and about the classification, arbitration was sought from a senior ophthalmologist. We adopted the modified Airlie House Classification in grading the photos. The classification was as follows:

• No DMR
• Non-Proliferative DMR - minimal, mild, moderate, severe
• Proliferative DMR - early, high risk, advanced
• Maculopathy - macular oedema, clinically significant macular oedema (CSME)

The clinical records of the studied population were retrieved and their data on duration of diabetes, treatment modality, smoking status, gender, most recent HbA1c level, blood pressure, blood cholesterol level and proteinuria by albustix were analysed. Risk factor analysis of DMR was assessed using this data.

Statistics

SPSS 11.0 statistical software was used for calculation of means, chi-square statistics, t tests and parametric tests. Multiple logistic regressions were used to analyse the predictors of diabetic retinopathy.

Results

Within the year 1999-2000, a total of 511 diabetic patients were invited to participate and all consented to have retinal photography. There were 48 (9.4%) of them whose examination was not successful, mainly because of dense cataract or inability to follow the instructions given by our nurses. As a result, a total of only 463 patients were included in the study. The age of the study population varied from 65 to 87 with a mean of 71 (SD: 4.37). There were 182 males and 281 females. Among them, 71.5% were on oral hypoglycaemic agents while the rest were on dietary control and none on insulin.

A total of 80 (17.3%) were found to have DMR. 142 (30.7%) subjects were newly diagnosed to have diabetes by the health screening, and 11 (7.7%) of them were found to have DMR. And among 321 (69.3%) subjects previously known diabetics, of whom 69 (21.5%) of them were found to have DMR (Table 1).

For those patients with DMR, 57 (71.2%) had minimal or mild non-proliferative retinopathy while 23 (28.8%) had referable DMR (defined as moderate non-proliferative retinopathy or worse, or clinically significant maculopathy in either or both eyes). The referable group represented 5% of all the 463 patients who had undergone retinal photography (Table 2).

As to the risk factors associated with the development of DMR, we had analysed the various parameters in association with all diabetic patients in this cohort as well as those previously known to have diabetes. These parameters included duration of diabetes, HbA1c level, blood pressure, total cholesterol level, age, smoking, gender, urine for albumin and current treatment regime. The results in Tables 3 and 4 showed that HbA1c and duration of diabetes were found to have significant association with DMR whereas other parameters did not. Multiple logistic regressions analysis also revealed that HbAlC level and duration of diabetes were strong predictors of DMR (Table 5). For the newly diagnosed diabetic patients, only 11 of them had DMR and the sample was too small for further analysis.

Discussion

This is a study on the prevalence of DMR among our local community-based elderly diabetic patients. There were 17.3% of them suffering from DMR. This is less than that found in other studies (21 to 48%). However, about 30% of these diabetic patients were newly diagnosed by the health assessment. Excluding this group of new patients, the rate of DMR for known diabetic subjects is revised to 21.5%. This is comparable to the prevalence of 21% found in the Oulu Eye Study which involved elderly diabetic patients aged 70 or above.¹⁹

For newly diagnosed type 2 diabetic patients, a local hospital study reported the rate of DMR to be approximately 22% in middle age population.⁹ In fact, up to 21% of patients with type 2 diabetes have been reported to have retinopathy at the time of first diagnosis of diabetes in adult populations.³ However, a Denmark study²⁰ found a prevalence of only 5% among newly diagnosed middle-aged and elderly diabetic patients. The Beaver Dam Eye Study reported a prevalence of 10% in the newly diagnosed type 2 diabetes mellitus in a population study aged from 43 to 84.²¹ The results of these studies were comparable to that obtained in our study (7.7%). The low prevalence rate may be due to 2 reasons. Firstly, our newly diagnosed diabetic patients were screened out by health assessment and they might be in a relatively early stage of their diabetic history. Secondly, these patients might perhaps run a different clinical course because of their relatively late onset of diabetes although this needs further study to verify. We found only 3 patients (3.7%) with proliferative DMR in this study. Other investigators also share the same experience that severe DMR is uncommon in elderly people.^19,22,23 This indicates that progression from non-proliferative to proliferative retinopathy may be less common in the elderly.

It has been estimated that over 60% of diabetic patients will have some degree of DMR after 20 years of diabetes.³ Our group, similar to Phillipov et al,²⁴ have shown that a duration of diabetes 7 years is an important risk factor in the development of DMR. HbA1c is a good indicator of diabetic control. It has been reported that for every % point decrease in HbA1c level (e.g. from 9% to 8%), there is a 35% reduction in the risk of microvascular complications.²⁵ Our study has shown that HbA1c level has a positive correlation with the development of DMR.

Since both albuminuria and DMR are the microvascular complications of diabetic patients, it is expected to see the two factors correlating with one another. However, this relationship could not be clearly demonstrated in the present study although the data suggests there was such a trend. Albustix was used in our clinics to detect proteinuria, and this might not be a sensitive method as compared to the measurement of urinary albumin excretion rate.

From our study, hypertension is not significantly associated with the development of DMR, and this is also shown in the studies by Phillipov et al²⁴ and Cahill et al.²⁶ McKay et al²⁷ also found that there is no significant association between tobacco use and the development of DMR and this is consistent with our findings.

The limitation of this study is the elderly patients were not randomly selected from the community. They were a biased sample from local elderly health centres. The general profile of elderly patients attending those elderly health centres had been described previously.²⁸ In general, they would be more health conscious and were leading healthier lifestyles than the general elderly population.

Those diabetic patients with a history of glaucoma were excluded and this may lower the prevalence and the severity of DMR in this study. However, there were only 0.2% of patients with glaucoma from 42,662 health assessments done by the Elderly Health Service in the same year. The detection of disease relied on retinal photography with sensitivities and specificities less than 100% and thus the prevalence may be underestimated. The ability of local primary care doctors in reading retinal photos had been assessed by Lam.²⁹ Our authors were included in Lam's study and it was shown that they belonged to the group who had achieved an overall of 97% sensitivity and 85-91% specificity in the interpretation of retinal photos.

Conclusion

DMR exists at a rate around 21.5% in elderly patients with known diabetes under primary care and proliferative DMR is not common. The risk factors associated with DMR are a high HbA1c level and a long history of DM. The rate is much lower (7.7%) for newly diagnosed diabetic patients who are screened out by routine health assessment. Perhaps our elderly population with late onset diabetes might run a different clinical course. Yearly screening of DMR for patients with diabetes has been recommended in most clinical guidelines on diabetes mellitus. Systematic screening programmes, however, are expensive. To improve the cost-effectiveness of these programmes, screening interval basing on baseline retinopathy has been suggested in some studies.^30,31 This article may echo that new onset diabetes in elderly subjects may not need annual screening for DMR initially if there is no retinopathy or retinopathy is of low grade at baseline. However, before embarking on this recommendation, a prospective study on the local population is necessary.

Acknowledgement

We are indebted to Dr Yung Hon-wah, ophthalmologist of Hospital Authority of Hong Kong, for his expert opinion and arbitration in the interpretation of retinal photos. We are also thankful to Ms Shelley Chan, research officer of Department of Health for her advice on statistical analysis.

Key messages

1. Diabetes mellitus retinopathy (DMR) is an important complication of diabetes mellitus (DM) and the most frequent cause of new cases of blindness among adults aged 20-74.
2. Early detection of DMR can substantially reduce the risk of visual impairment.
3. Retinal photography is a better method for screening DMR than direct ophthalmoscopy.
4. Among the local elderly Chinese (aged 65), it has been found that DMR exists at a rate of 21.5% in those with a known history of DM and 7.7% in those newly diagnosed diabetics from routine health assessment.
5. A higher HbA1c level and a longer duration of DM are found to be associated with the development of DMR.
6. Retinal photography can be employed as an effective screening method for DMR in a primary care setting.