fact that red dots is the initial funduscopically visible lesion implies that the presence of white lesions occuring alone are not hard exudates. This may be an important diagnostic parameter especially in older type 2 diabetic patients where white lesions may represent drusen secondary to age-related maculopathy. Small sharply delimited whitish drusen that are difficult to differentiate from exudates may also occur in younger persons. However, these lesions can be identified by repeating the examination after more than 1 month where drusen will be unchanged, whereas the dynamic nature of exudates implies that this lesion will always have a changed size, location or configuration.

The fact that exudates often arrange in rings around a leakage point with a microaneurysm and/or a haemorrhage in the centre demonstrates an interdependence between these two lesion types with the red dot being the immediate response and the hard exudate the more sustained response to a localised vascular abnormality. The radius of the exudate ring will represent the diffusion distance from the leakage point to the point of plasma protein precipitation.

The presence of haemorrhages and retinal oedema without exudates may be observed in diabetic maculopathy of the ischaemic type. Ischaemic maculopathy may be difficult to diagnose without fluorescein angiography to show the typical capillary occlusion.

Visual Impairment in Diabetic Retinopathy

The general purpose of the management of diabetic retinopathy is to prevent impairment of central vision secondary to the two complications diabetic maculopathy and proliferative diabetic retinopathy. However, several other types of visual impairment may occur in diabetic patients. Generalised changes such as subclinical perturbations in the electroretinogram [2] may not be appreciated by the patient, whereas

changes in contrast sensitivity, dark adaptation and the peripheral visual field induced by retinal photocoagulation may be serious adverse effects that limit normal activities [61, 62]. However, the individual retinopathy lesions may also affect visual function, the severity of symptoms depending on the size and the location of the retinal area involved. Table 2 gives an overview of these different types of visual impairment in diabetic retinopathy [23, 63].

It appears that individual retinal lesions can affect visual function through a variety of mechanisms and may contribute to the visual dysfunction experienced by diabetic patients. The fact that the morphological lesions correlate with functional pathology in diabetic patients is important for understanding how the disease leads to visual loss.

Conclusions

The diagnosis and management of diabetic retinopathy depends on both the correct detection of morphological lesions related to impaired retinal vascular supply, and the correct interpretation of the dynamics, the relative occurrence, and the spatial distribution of these lesions in the ocular fundus. The pathological correlates of these changes include anatomical changes that can be studied by clinical inspection and by histopathological techniques, and functional changes that can be studied by electrophysiological or psychophysical examination techniques. Therefore, these approaches are necessary in order to distinguish the disease patterns that are unique for diabetic retinopathy from those seen in retinal vascular diseases in general. This is crucial for gaining a deeper insight into the pathophysiology of diabetic retinopathy and for improving screening, diagnosis and treatment of diabetic retinopathy in the future.

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