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Aims: To compare the macular capillary blood flow of patients with clinically significant diabetic macular oedema (DMO) with that of non-diabetic subjects and to determine the relation between blood flow and capillary leakage in patients with DMO. Methods: The sample comprised 45 non-diabetic subjects (mean age 59 years) and 18 type 2 patients with clinically significant DMO (mean age 60 years). Macular capillary blood flow measurements were acquired using the Heidelberg retina flowmeter (HRF) and a 10˚62.5˚scan field centred on the fovea. Fluorescein angiography was undertaken on each of the diabetic patients after the completion of HRF measurements. Results: Temporal macular capillary blood flow was significantly lower for the patients with clinically significant DMO compared with age matched non-diabetic subjects (ANCOVA, p = 0.0011) while relative nasal-temporal asymmetry of macular capillary blood flow was significantly higher (p = 0.0125). Nasal-temporal asymmetry of macular capillary blood flow was significantly higher for the patients with DMO and capillary leakage within the scan area (two tailed t test, p = 0.0071). Macular capillary blood flow was always lower in areas of DMO and capillary leakage. Conclusion: Capillary blood flow was reduced in areas of DMO and capillary leakage, suggesting the presence of a localised perturbation of capillary blood flow regulation. R etinal capillaries lack an autonomic nerve supply but they are thought to have an intrinsic ability to constrict or dilate-that is, autoregulate, in order to ensure adequate blood flow to retinal tissues under changing conditions. 1 In addition, autoregulation is thought to be primarily facilitated by the vascular reactivity of upstream arterioles. Disturbance of retinal capillary blood flow is a feature of many ocular diseases, including diabetic retinopathy and glaucoma. A number of non-invasive instruments have been designed to measure retinal haemodynamics. 2-5Scanning laser Doppler flowmetry (SLDF-that is, the combination of a laser Doppler flowmeter and a scanning laser system) is unique in that it provides a two dimensional quantifiable perfusion map of retinal capillary blood flow rather than a measurement of flow at a single point.6 SLDF has potential as a clinical tool to non-invasively visualise and quantify retinal capillary blood flow. [6][7][8] Retinal capillary blood flow disturbance is fundamental to the pathogenesis of diabetic retinopathy. However, retinal blood flow as measured in the major retinal vessels of patients with diabetic retinopathy is reported by some to be reduced 9-11 and by others to be increased 1 12-14 when compared to non-diabetic subjects, in part depending on the severity of the retinopathy or on the heterogeneity of the group. This study focuses on diabetic patients with diabetic macular oedema (DMO) and on the macular capillary circulation. Macular oedema is the leading cause of visual impairment and legal blindness in people with diabetes. 15 To the best of our knowledge, no studies have investi...

Significant differences in retinal capillary perfusion were found across the macular region and corresponded with the increase in capillary beds. The Heidelberg Retina Flowmeter also measured the expected decrease in volume at the foveolar avascular zone. There were no significant interocular differences in perfusion. Eye movements, media opacities, and poor tear film quality had a deleterious effect on image quality.