ORIGINAL ARTICLES
PREVALENCE OF DIABETIC RETINOPATHY IN A PRIMARY CARE SETTING
USING DIGITAL RETINAL IMAGING TECHNOLOGY
Keah Say Hien FRACGP, Elizabeth Medical Centre, Muar,
Johor.
Chng Kooi Seng FRACGP AM, Klinik Chng, Johor Bahru, Johor.
Table 1. International Clinical Diabetic Retinopathy (DR) Disease Severity Scale
| Proposed disease severity level |
Findings observable with dilated
ophthalmoscopy |
| No apparent DR | No abnormalities |
| Mild nonproliferative DR | Microaneurysms only |
| Moderate nonproliferative DR | More than “mild” but less than “severe” |
| Severe nonproliferative DR | Any of the following:
|
| Proliferative DR | 1 or more of the following :
|
Table 2. International Clinical Diabetic Macular Edema (DME) Disease Severity Scale
| Proposed disease severity level |
Findings on dilated ophthalmoscopy |
| DME absent | No retinal thickening or hard exudates present in posterior pole |
| DME present | Some retinal thickening or hard exudates present in posterior pole |
| If DME is present, it can be categorised as follows: | |
| Mild DME | Some retinal thickening or hard exudates in posterior pole but distant from the centre of the macula |
| Moderate DME | Retinal thickening or hard exudates approaching the centre of the macula but not involving the centre |
| Severe DME | Retinal thickening or hard exudates involving the centre of the macula |
RESULTS
Demographic characteristics
215 diabetic patients were seen during the study period, and 200 fulfilled
the selection criteria. The mean age was 57.4 years (range 27-82 years).
Most of the respondents were Chinese (86%), the rest were Malays (9.5%)
and Indians (4.5%). Forty-four percent of them were males.
Clinical data
The duration of their diabetes was: <1 year 18%, 1-5 years 36%, 5-10
years 24.5, and >10 years 21.5%. One hundred and four of them had concomitant
hypertension (53.1%). One-quarter of them had ever been seen by an ophthalmologist.
These included the subjects consulting the ophthalmologist for diseases
other than diabetes, for treatment of cataracts and for screening purposes.
Cataracts were present in 25% of the patients studied. Very few patients
(6.5%) ever received laser photocoagulation for their retinopathy. Only
12% of the patients in the study had visual acuity of 6/12 or worse in
the better eye.
Retinal photography
Mydriatic eye drops were used in 26% of the patients studied (52 cases).
Retinal photographs of four patients were unreadable; hence the calculation
of the prevalence of retinopathy was based on 196 patients. Ninety-three
patients (47.4%) were found to have retinopathy. The severity of retinopathy
(based on the International Clinical Diabetic Retinopathy Disease Severity
Scale) was as follow: mild nonproliferative 16.3%, moderate nonproliferative
26%, severe nonproliferative 3.1%, and proliferative 2.1%. The prevalence
of maculopathy was 59.2% (based on the International Clinical Diabetic
Macular Edema Disease Severity Scale): mild (hard exudates away from the
macula) 2%, moderate (hard exudates within the macula but not involving
the fovea) 37.3%, and severe (hard exudates encroaching upon the centre
of the macula) 19.9%. Overall, 71.9% of these diabetic patients had either
retinopathy or maculopathy and 34.7% had both retinopathy and maculopathy.
Sight threatening eye disease (STED, defined as moderate nonproliferative
diabetic retinopathy or worse, circinate maculopathy and hard exudates
within 1 disc diameter from the centre of the fovea) occurred in 80 cases
(40.8%).
Among these diabetic patients with concomitant hypertension, retinopathy was detected in 76 (38.8%). As shown in Table 3, most diabetic patients already had retinopathy when they sought medical treatment for their diabetes.
Table 3. Prevalence of diabetic retinopathy compared with duration of diabetes
| Duration of diabetes | No of cases | Diabetic retinopathy (%) |
| < 1 year | 36 | 63.9 |
| 1-5 years | 71 | 74.6 |
| >5 years | 89 | 75.3 |
DISCUSSION
The conventional method of screening for diabetic retinopathy involves
direct ophthalmoscopy using a hand-held ophthalmoscope. It may be a daunting
procedure for some doctors and requires dark room facilities and pupillary
dilatation. It allows only a two-dimensional view of the retina and a
photographic recording is not possible. It is thus not recommended as
a sole screening instrument in large scale screening programmes.
The current clinical gold standard for assessing the level of diabetic
retinopathy is through the grading of seven standard field 35-mm stereoscopic
colour fundus photography taken through a dilated pupil using the Early
Treatment Diabetic Retinopathy Study (ETDRS) protocols. The ETDRS 35-mm
retinal photography and grading protocols have an established and documented
sensitivity for detecting and assessing level of diabetic retinopathy.4
The disadvantages with 35-mm photography are the requirements for skilled
operators, the need for pupil dilatation, the lengthy sessions for the
patients, the higher costs of film and film handling, and inefficient
archiving with the potential for loss of data and loss or damage of slides.
Digital fundus imaging has revolutionalised retinal screening. The optical components of the retinal imaging system have not changed from the traditional photography system; rather the film camera back has been replaced by a video camera. A number of novel retinal imaging systems were soon developed including the Joslin Vision Network5 which is a telemedicine application for the management of diabetes in general and diabetic eye care specifically.
Imaging or testing strategies will thus vary with the cost-effective strategies of the individual medical community. The systems adopted can be categorised to include the various camera types (mydriatic versus non-mydriatic), capture media (35-mm slide film, Polaroid, digital imaging ), image resolution, number of fields (seven, four, three, two, one ), field of view (30°, 45°, 60°) and whether or not images are stereoscopic. For example the imaging system used in this study, the Topcon TRC NW 200 is a 45° nonmydriatic digital imaging system, 3.15 mega pixel image resolution, 3 fields availability (macular, nasal and temporal ), and non-stereoscopic.