David Levy, MD, FRCP
Diabetic retinopathy is the most common clinically significant microvascular complication of diabetes, but cataract is the most common ocular complication, with a prevalence of about 60% in those aged 30–54, five times more frequent than in those without diabetes. Diabetes is also associated with raised intraocular pressure and chronic open-angle glaucoma, and retinal venous and arterial occlusions are also more common. Neovascular age-related macular degeneration (AMD) and diabetic retinopathy have pathogenic features in common (and also some treatment options), and macular degeneration is more common in people with vascular disease, such as hypertension or history of myocardial infarction, though there is no clear link with diabetes. Comprehensive eye screening in diabetes should therefore include all these important pathologies as well as others unrelated to diabetes, including simple refraction problems. Fear of visual loss is common, recurrent and pervasive in many people with diabetes, and is independent of objective measures of retinopathy and visual acuity. The fear is rarely articulated spontaneously, but must be recognized by the diabetes team….
The widespread introduction of retinopathy screening programmes has reduced the need for routine retinal examination in both primary and secondary care. Nevertheless, skilled direct ophthalmoscopy is still an important procedure (Box 9.1). While tight glycemic control may not be as important in the management of retinopathy in type 2 diabetes as was previously believed, DCCT/EDIC confirms that glycemia is the main, possibly the only, driving force behind early retinopathy in type 1 diabetes, while multimodal management of type 2 diabetes remains critical. The significance of retinopathy therefore varies with the individual, and is much wider than a referral pathway to the ophthalmology service.
Retinopathy in type 1 diabetes
Clinically significant retinopathy is uncommon within 5 years of diagnosis, but in the population screened for the DCCT, two-thirds with duration of less than 5 years had some detectable retinopathy.
Undoubtedly the natural history has changed. The Wisconsin study, published in the mid-1980s, showed a near-100% prevalence of some degree of retinopathy after 15–20 years of type 1 diabetes, with proliferative retinopathy peaking at about 60% at 20–35 years’ duration, and severe visual impairment in 2.4%. By the early 2000s, at least in Oslo, Norway, the prevalence of proliferative retinopathy at the same duration was only 11%, and in the intensively treated DCCT group fewer than 1% were blind . This gratifying reduction must be due to improved long-term glycemic control, but strangely there is little evidence that this has occurred. Patients with 20–24 years’ duration, especially those with onset before age 15 years, are at the greatest risk of developing proliferative retinopathy; ensure this group has regular retinal screening.
Retinopathy in type 2 diabetes
The picture is quite different in type 2 diabetes, where 20–30% have retinopathy at diagnosis, and 10–25% proliferative retinopathy 10 years after diagnosis. Evidence is conflicting whether blindness caused by diabetic retinopathy is decreasing; however, as recently as 2004, diabetes was still the commonest cause of blindness and visual impairment in working-age people in western Scotland. However, do not underestimate the visual impact of less severe retinopathy; for example, patients with macular oedema have impaired quality of life similar in degree to non-diabetic patients with AMD .
Classification of retinopathy
The clinical classification of retinopathy remains important to the clinician and the patient, whereas the many and complex grading systems for severity of retinopathy are more relevant to the epidemiologist and clinical trialist. A simple international retinopathy severity scale has been proposed based on the presence of red lesions only, but the following notes use the more traditional classification of:
- non-proliferative diabetic retinopathy (NPDR)
- pre-proliferative diabetic retinopathy
- proliferative diabetic retinopathy
- advanced diabetic eye disease.
- Nathan DM, Zinman B, Cleary PA et al. Modern-day clinical course of type 1 diabetes mellitus after 30 years’ duration: the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications and Pittsburgh epidemiology of diabetes complications experience (1983–2005). Arch Intern Med 2009;169:1307–16. PMID: 19636033.
- Hariprasad SM, Mieler WF, Grassi M, Green JL, Jager RD, Miller L. Vision-related quality of life in patients with diabetic macular oedema. Br J Ophthalmol 2008;92:89–92. PMID: 17584999.
- Beulens JW, Patel A, Vingerling JR et al. Effects of blood pressure lowering and intensive glucose control on the incidence and progression of retinopathy in patients with type 2 diabetes mellitus: a randomised controlled trial. Diabetologia 2009;52:2027–36. PMID: 19633827.
- Chew EY, Ambrosius WT, Davis MD et al. Effects of medical therapies on retinopathy progression in type 2 diabetes. ACCORD Study Group and ACCORD Eye Study Group. N Engl J Med 2010;363:233–44.
- Chaturvedi N, Porta M, Klein R et al. Effect of candesartan on prevention (DIRECT-Prevent 1) and progression (DIRECT-Protect 1) of retinopathy in type 1 diabetes: randomised, placebo-controlled trials. Lancet 2008;372:1394–402. PMID: 18823656.
- Sjølie AK, Klein R, Porta M et al. Effect of candesartan on progression and regression of retinopathy in type 2 diabetes (DIRECT-Protect 2): a randomised placebo-controlled trial. Lancet 2008;372:1385–93. PMID: 18823658.
- Reaven PD, Emanuelle N, Moritz T et al. Proliferative diabetic retinopathy in type 2 patients is related to coronary artery calcium in the Veterans Affairs Diabetes Trial (VADT). Diabetes Care 2008;31:952–7. PMID: 18316393.
- Al-Ansari SA, Tennant MT, Freve MD, Hinz BJ, Senior PA. Short report: sub-optimal diabetes care in high-risk diabetic patients attending a specialist retina clinic. Diabetic Med 2009;26:1296–300. PMID: 20002485.
- Shah AS, Chen SH. Cataract surgery and diabetes. Curr Opin Ophthalmol 2010;21:4–9. PMID: 19935423.
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David Levy, MD, FRCP, Consultant Physician, Gillian Hanson Centre, Whipps Cross University Hospital; Honorary Senior Lecturer
Queen Mary University of London London, UK
This edition first published 2011, © 2011 by David Levy. 1st edition 1998 (Greenwich Medical Media/Cambridge University Press) 2nd edition 2006 (Altman Publications)