Tuesday , November 21 2017
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Handbook of Diabetes, 4th Ed., Excerpt #14: Diabetic Eye Disease

Rudy Bilous, MD, FRCP
Richard Donnelly, MD, PHD, FRCP, FRACP

handbook-of-diabetes-image

Diabetic eye disease primarily affects the retinal vasculature, but the iris and lens can also be involved. Most people with diabetes will show signs of retinopathy after 25 years duration, but only a minority progress to the severest form. Photocoagulation has revolutionized the treatment of retinopathy but even so, diabetes remains a significant cause of visual loss in the working-age population in the UK, and adults with diabetes compared to those without in the USA have 1.85 times the risk of having a non-correctable reduction in visual acuity….

Pathology and clinical appearances: Retinopathy

Essentially, diabetic retinopathy can be classified as non-proliferative (now often split into background and pre-proliferative) and proliferative.

 

The earliest pathological features are thickening of the retinal capillary basement membrane, loss of tight junctions in the retinal endothelium, and loss of pericytes, which are the contractile cells enveloping the capillaries and which control vessel and thus perfusion (Figure 15.1). Physiologically, an increase in retinal blood flow is an early feature of diabetes and it is possible that this creates mechanical stress that leads to endothelial separation and pericyte loss.

 

 

The first noticeable lesions on ophthalmoscopy are micro-aneurysms, which appear as small red dots varying in size from 20 to 200μm in diameter (Figures 15.2, 15.3). They are blind pouches arising from capillaries, probably from weakened endothelial cell junctions adjacent to an area of pericyte loss. Microaneurysms are rarely sight threatening (unless occurring in the macula) and can seem to disappear although this is probably a result of thrombosis within the aneurysm or closure of the feeding capillary. Capillary closure is a feature of advancing retinopathy and the resultant ischemia is a driver for subsequent proliferation.

Hemorrhages can occur superficially when they tend to be flame-shaped (limited by nerve fibers) or deep (blot or round-shaped and indicative of underlying ischemia) (Figure 15.4).

Hard exudates are the result of leakage of lipid rich proteins into the retina (Figure 15.5). They appear as discrete yellow-creamy white patches, which are often ring-shaped or circinate around a central area of ischemia and capillary leakage.

Capillary closure causes microinfarcts in the nerve fiber layer and these appear as indistinct white patches and are termed cotton wool spots (previously known as soft exudates) (Figure 15.6). More advanced ischemia results with the development of intraretinal microvascular abnormalities (IRMAs) (Figure 15.7), which are clumps of small irregularly branching vessels within the retina, and venous dilatation, beading (segmental dilatation resembling a string of sausages) (Figure 15.8), loops and reduplication, sometimes into multiple loops resembling a four-leafed clover.