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Background: The severity of diabetic retinopathy is well known to have a close association with the duration of diabetes mellitus. Patients with recently diagnosed diabetes should have adequate eye examinations to eliminate the possibility of diabetic retinopathy being present because there is no accurate means of determining the duration of the disease. The prevalence of diabetic retinopathy in type 2 diabetic patients with known duration up to one year was investigated in the present study.
Methods: A centre for diabetic retinopathy screening was set up in a community in Hong Kong. The screening procedures included history taking, visual acuity measurement, anterior ocular health assessment and retinal examination by fundus photography. Fundus photographs were taken in nine different positions of gaze through natural or dilated pupils. Using the criteria recommended by the American Optometric Association the retinopathy was graded in severity. ‘Recently diagnosed diabetes mellitus’ was defined as having diabetes diagnosed by a physician within the previous year.
Results: A total of 12,112 patients having their first visits to the centre were recruited from 2006 to 2009. Among them, 3,510 patients had recently diagnosed diabetes. The mean age of patients was 59.5 years. The prevalence of diabetic retinopathy was 18.2 per cent (639 patients) among the recently diagnosed diabetic patients. Most of the patients had mild non-proliferative diabetic retinopathy. In these 639 patients, approximately seven per cent had sight-threatening retinopathy that included significant macular oedema, all of whom required monitoring. The presence of hypertension or smoking was not significantly associated with the prevalence of diabetic retinopathy in recently diagnosed diabetic patients.
Conclusions: Screening for diabetic retinopathy is important for newly diagnosed diabetic patients. In Hong Kong, the prevalence of diabetic retinopathy was alarmingly high and some patients had already developed sight-threatening retinopathy that included macular oedema. Most of them had no symptoms until the retinopathy progressed and they developed macular oedema. A systematic screening program in the community is needed for early detection and to reduce blindness in diabetic patients.
Diabetes mellitus (DM) has always been an important public health concern. It has been estimated that approximately 10 per cent of the total population of Hong Kong are diabetic.1,2 Diabetic retinopathy (DR) is one of the micro-vascular complications of diabetes, which may not have symptoms in the early stages. Control of these complications depends on proper management and monitoring of retinal status and blood glucose levels after the early detection of retinopathy but may progress to a sight-threatening stage if left untreated. Early photocoagulation was found to be beneficial to patients with sight-threatening retinopathy, especially with significant macular oedema.3–5 Diabetic retinopathy screening is vital for diabetic patients to have early detection and management of their retinopathy and to reduce the risk of sight-threatening complications.
In one epidemiological study,6 the prevalence of diabetic retinopathy in Hong Kong was 28.4 per cent with a mean duration of diabetes of 4.71 years. There was a higher prevalence of retinopathy in patients with a longer duration of diabetes.7 The need for regular observation of patients with background retinopathy has been stressed due to the progressive nature of the retinopathy,8,9 and therefore screening would help reduce visual loss.10 Studies in different countries have proved the effectiveness of using retinal photography for the detection of diabetic retinopathy.11–14
The DR screening program in our clinic started in 2005. The aim of the program was to increase the awareness of regular eye examinations for diabetic patients and facilitate the collaboration of physicians and optometrists. Retinal photographs were taken using a digital retinal camera. Our study investigated the prevalence of diabetic retinopathy in diabetic patients with known duration since first diagnosis of up to one year. We also compared the prevalence of retinopathy in patients with different durations of diabetes since first diagnosis and the possible risk factors associated with diabetic retinopathy.
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There were 12,112 patients with good quality fundus photographs who attended our clinic for their first screening for diabetic retinopathy during January 2006 to August 2009. There were 3,510 patients with a diagnosis of diabetes within one year. Their general characteristics are listed in Table 1. There were slightly more female (51.6 per cent) than male patients, with a mean age of 59.46 ± 10.86 years (range, 18 to 89 years). The majority of patients (89.4 per cent) had never smoked. More than half (58.6 per cent) of the patients presented with hypertension. Almost half (44.3 per cent) of the patients had oral diabetic medication. There were no insulin users among these patients.
Table 1. General characteristics of patients with known duration of up to one year since the diagnosis of diabetes mellitus
|Characteristics||Number of patients|
|Total number of patients||3,510|
| Male (%)||1,699 (48.4%)|
| Female (%)||1,811 (51.6%)|
|Mean age ± SD (range) (years)||59.46 ± 10.86 (18–89)|
|Smoking status|| |
| Ever smoked (%)||371 (10.6%)|
| Never smoked (%)||3,139 (89.4%)|
| Yes||2,057 (58.6%)|
| No||1,453 (41.4%)|
|Treatment type|| |
| Diet control (%)||1,954 (55.7%)|
| Oral medication (%)||1,556 (44.3%)|
| Insulin injection (%)||0 (0%)|
The prevalence of diabetic retinopathy in patients with a diagnosis of diabetes up to one year was 18.2 per cent (639 patients). The grading of retinopathy is summarised in Table 2. Among them, 6.89 per cent (39) had sight-threatening retinopathy (graded as severe non-proliferative diabetic retinopathy or worse, or having central serous macular oedema with mild or moderate non-proliferative diabetic retinopathy) and needed further treatment by an ophthalmologist.
Table 2. Retinal status of 12,112 patients showing the number and prevalence (%) of known durations since the diagnosis of diabetes
|Duration||≤1 year||2–5 years||6–10 years||>10 years|
|No DR||2,871 (81.8)||3,060 (74.0)||1,864 (67.0)||924 (54.8)|
|Mild NPDR||545 (15.6)||924 (22.4)||779 (28)||593 (35.2)|
|Moderate NPDR||55 (1.6)||107 (2.6)||99 (3.6)||115 (6.8)|
|Severe NPDR||28 (0.8)||30 (0.7)||32 (1.2)||39 (2.3)|
|Very severe NPDR||3 (0.1)||5 (0.1)||3 (0.1)||7 (0.4)|
|Proliferative DR||8 (0.2)||7 (0.2)||5 (0.2)||9 (0.5)|
The prevalence of retinopathy increased with a longer duration of diabetes since diagnosis from 26.0 per cent (duration of two to five years) to 33.0 per cent (duration of six to 10 years) and 45.2 per cent (duration over 10 years), as shown in Table 2. Considering the percentage of sight-threatening retinopathy, it was the second highest (6.89 per cent) in newly diagnosed patients (Table 3).
Table 3. Percentage of sight-threatening retinopathy in patients with diabetic retinopathy
|Duration||≤1 year||2–5 years||6–10 years||>10 years|
|Number of patients with severe NPDR or worse (with or without CSME)||39||42||40||55|
|Number of patients with mild or moderate NPDR (with CSME)||5||9||9||9|
|Total number of patients with sight-threatening retinopathy||44||51||49||64|
The Chi-squared test showed that neither hypertension nor smoking had a significant effect on the prevalence of diabetic retinopathy in newly diagnosed diabetic patients (Pearson Chi-squared value = 2.142, p = 0.143 and Pearson Chi-squared value = 0.254, p = 0.614, respectively).
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It is estimated that there are 700,000 (approximately 10 per cent of the population) diabetic patients in Hong Kong and there is a trend towards younger adults being diagnosed with diabetes in developed countries.16–18 Many studies have shown that poorly controlled, unbalanced diet and lack of regular exercise might contribute to this trend.18–20 Diabetic retinopathy is a complication of diabetes and one of the worldwide leading causes of blindness.21–23 Early detection with regular examinations and management of the disease are effective measures to reduce the chance of blindness due to sight-threatening retinopathy.8,21,24 Therefore, screening for retinopathy is recommended for all diabetic patients, particularly at the time of first diagnosis.
The prevalence of diabetic retinopathy in patients up to one year since the diagnosis of diabetes was 18.2 per cent. This is lower than a previous epidemiological study in Hong Kong.6 The known duration since diagnosis of selected diabetic patients in our study was up to one year, whereas diabetic patients included in the epidemiological study had a mean known duration of 4.71 years, with a range from 0.1 to 40.6 years. A difference in the known duration of diabetes might lead to the lower prevalence in the present study.
Our electronic system records ‘greater than 15’ if the known duration of diabetes is over 15 years, which made it difficult to calculate the mean and range of known duration of diabetes. The prevalence of diabetic retinopathy regardless of the duration since diagnosis in the present study (28.0 per cent) was similar to previous studies in Hong Kong6 (28.4 per cent) and Victoria, Australia25 (29.1 per cent); however, it was lower than studies in the United States (33.2 per cent),26 Singapore (35.0 per cent)27 and China (37 per cent).28 Different races such as Black people, Hispanics, Caucasians and Chinese were included in the US study, while the majority of patients recruited in the present study were Chinese. Moreover, sample sizes were generally lower in other studies; there were 778 in the US study, 3,261 in the study in Singapore and 235 in the Chinese study. These factors might account for the differences in prevalence of diabetic retinopathy among these studies.
The prevalence was lower in India (18.0 per cent).29 Insufficient public awareness of diabetic retinopathy and lack of health checks might result in undiagnosed diabetes in the Indian population, and therefore a lower prevalence of diabetic retinopathy might be expected. Modes of diet may also contribute to the difference of prevalence of diabetic retinopathy among countries and this requires further investigation.
Similar to other epidemiological studies,6,30,31 our research shows an increase in the prevalence of diabetic retinopathy with longer durations since the diagnosis of diabetes. When we refer to Table 3 showing the percentage of patients with sight-threatening retinopathy with different durations since the diagnosis of diabetes, the percentage in ‘newly diagnosed’ patients was actually higher (6.89 per cent) than other durations except over 10 years. This was mainly due to the major increase in patients with mild and moderate non-proliferative diabetic retinopathy who had a longer duration since the diagnosis of diabetes, rather than those with sight-threatening retinopathy.
The onset of diabetes could be years longer than the time of diagnosis. Patients may not be aware of the diabetes until they experience symptoms, such as frequent urination, unusual thirst, extreme hunger, unusual weight loss or extreme fatigue and irritability. Therefore, those labelled as ‘newly diagnosed’ did not mean ‘newly onset’ of diabetes. Considering the alarming prevalence of diabetic retinopathy in newly diagnosed diabetic patients and its percentage of sight-threatening retinopathy, retinal screening should be indicated as soon as patients are diagnosed with diabetes.
Tight control of blood glucose is effective in reducing the rate of progression of diabetic retinopathy and therefore the association between blood glucose level and diabetic retinopathy has been investigated.32 Levels of HbA1c were not available for some patients and random glucose levels are affected by many factors including the time since the last meal. In the present study, blood glucose levels were excluded in our evaluation of risk factors associated with the prevalence of diabetic retinopathy.
Blood glucose levels may be controlled by diet, oral medication or insulin injections. There were no insulin users in the present study. All recruited subjects who were not receiving oral medication said they used diet control. Reporting bias might affect this result because many patients knew that an intake of too much sugar and carbohydrates made it difficult to control diabetes. Instead of admitting that they do nothing, they might claim to use diet control.
From our results, hypertension had no significant effect on the prevalence of diabetic retinopathy in newly diagnosed diabetic patients. One explanation is that control of tight blood pressure is more important to the progression of established retinopathy than the onset of diabetic retinopathy.30 Hypertension is a risk factor of macro-vascular and micro-vascular complications and diabetic retinopathy is a micro-vascular disease.33 Tight control of blood pressure in diabetic patients (mean duration was 2.6 years) with hypertension would have less retinal signs (microaneurysms, hard exudates and cotton-wool spots) than those with less blood pressure control.34 These differences were noticed after a 7.5-year follow-up period. From the Action to Control Cardiovascular Risk in Diabetes study,32 careful glycaemic control and intensive treatment of dyslipidaemia reduced the rate of progression of diabetic retinopathy but intensive blood pressure control did not. Therefore, hypertension seems to have little effect on the prevalence of diabetic retinopathy in newly diagnosed diabetic patients.
Cigarette smoking is a risk factor for complications of diabetes, especially cardiovascular disease;35 however, smoking had little effect on the prevalence and incidence of diabetic retinopathy in this and other36,37 epidemiological studies, even though our smoking prevalence was lower. Only patients who were current smokers during attendance at the clinic were classified as ‘ever smoked’. Reporting bias might further decrease the number of smokers because patients might feel guilty about smoking and give misleading information.