Diabetes and diabetic retinopathy

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Diabetes mellitus is on the increase. Hilary King and Marian Rewers, on behalf of the WHO Ad Hoc Diabetes Reporting Group, write in this issue of Community Eye Health that there is an apparent epidemic of diabetes amongst adult populations of disadvantaged communities, both in developing countries and also in the industrialised world.

For every patient who is known to have diabetes another has the disease unawares.¹ It is a significant cause of multisystem disease, including cardiovascular disease, renal failure – and blindness.

The diagnosis of diabetes

Although the diagnosis of diabetes may be anticipated when classical symptoms and signs are present; weight loss, fatigue, a history of polydipsia (excessive thirst) and polyuria (excessive urinating), the diagnosis should not rely only on the presence of glycosuria (sugar in the urine). The diagnosis must be confirmed by demonstrating the presence of fasting hyperglycaemia (raised blood sugar) and following an oral glucose tolerance test.²

Diabetic retinopathy and blindness

Twenty years after the onset of diabetes nearly all patients with type I diabetes (insulin-dependent) and more than 60% of those with type II diabetes (non insulin-dependent) will have retinopathy.³ Diabetic retinopathy is the leading cause of blindness amongst people of working age in industrialised countries.⁴ It is estimated that there are 20 million diabetics in the Middle East (WHO Eastern Mediterranean Region), of which 800,000 will require treatment for retinopathy, and 116,000 new patients will present for treatment each year.⁵ In Singapore, 8.6% of the population between 15 and 69 years is diabetic, that is, 165,000 diabetics and at least 16,500 of these will have retinopathy.⁶

Ricky Sharma writes in this issue of his experience at Aravind Eye Hospital, South India. In a six month period, 1,863 new eye patients had a diagnosis (either previously known or unknown) of diabetes mellitus. Of these, 684 (37%) were found to have diabetic retinopathy. Further, 987 (53%) had either immature or mature cataracts and so some retinopathy will have been obscured.

Thylefors, Negrel, Pararajasegaram and Dadzie, in their analysis of the WHO Global Data Bank on Blindness, said that the survey data on diabetic retinopathy as a cause of blindness is too limited to reach an accurate figure.⁷ However, it does seem likely that blinding diabetic eye disease is now the fourth major cause of blindness worldwide, after cataract, the glaucomas and trachoma.

Philip Hykin, in his review article, describes the clinical features and management of diabetic retinopathy. The new descriptive terms used by the Early Treatment of Diabetic Retinopathy Study (ETDRS) should be understood by us all (see Table).

Screening and treatment

Lyn Jenkins and Valerie Mayon-White address the difficult question of screening for diabetic retinopathy. Although the ‘ideal screening method does not exist’ and many in developing countries will not have available sophisticated equipment for screening, all eye care workers should be aware if diabetes is a public health problem in their region and make sure that diabetic patients have regular, dilated view ophthalmoscopy according to the guidelines given in Table 1, page 59 of this issue.

Diabetic retinopathy terms

It is understood that adding retinal photography to direct or indirect ophthalmoscopy greatly improves sensitivity and specificity (see definitions on page 54) in identifying diabetic retinopathy.^5,7,8 However, Yeo, Lim and colleagues rightly point out that ‘primary health care and other practitioners should … be encouraged to attempt direct ophthalmoscopy … and refer diabetics for further examination if the fundal state cannot be adequately assessed by them.’⁶

Early treatment using laser photocoagulation has been shown to reduce blindness due to diabetic retinopathy by at least 60% and the figure will improve further as patients at risk are identified early:³ the earlier the better.

Recognition of the increasing problem of diabetes mellitus and its danger to sight, training in ophthalmoscopy (and other diagnostic methods, if possible), early identification of the stages of retinopathy in patients at risk and referral for expert opinion and treatment, will prevent blindness for many individuals in vulnerable communities around the world.

References

1 Diabetes 2000 Project Leaflet, “Elimination of preventable blindness from diabetes by the year 2000”. American Academy of Ophthalmology, USA.

2 WHO Technical Report Series 844, Prevention of diabetes mellitus: report of a WHO study group. Geneva: WHO, 1994.

3 American College of Physicians, American Diabetes Association and American Academy of Ophthalmology. Screening guidelines for diabetic retinopathy. Ophthalmology 1992; 99: 1626-8.

4 Kohner EN, Porta M. Screening for Diabetic Retinopathy in Europe: A Field Guide-Book. Copenhagen: WHO Regional Office for Europe, 1992.

5 Ahmed AA. Prevention of blindness due to diabetes in the Middle East (Editorial). Middle East J Ophthalmol 1994; 2: 68-9.

6 Yeo KT, Lim ASM, Ling SL, Lau HC, et al. Mass screening for diabetic retinopathy in the prevention of blindness. Asia-Pacific J Ophthalmol 1995; 7: 2-8.

7 Thylefors B, Negrel A-D, Pararajasegaram R, Dadzie KY. Global data on blindness. Bull WHO 1995; 73(1): 115-21.

8 O’Hare JP, Hopper A, Madhaven C, Charny M, et al. Adding retinal photography to screening for diabetic retinopathy: a prospective study in primary care. BMJ 1996; 312: 679-82.

9 Ryder B. Screening for diabetic retinopathy. BMJ 1995; 311: 207-8.