Hypoglycaemia is associated with the absence of a decrease in diurnal macular thickness in patients with diabetic macular oedema

Aim. - Spontaneous diurnal variations measured by optical coherence tomography (OCT) have been reported in diabetic macular oedema (DME) together with a daytime decrease in central macular thickness (CMT). For this reason, this study aimed to investigate the influence of acute glucose and blood pressure changes on daytime variations in CMT in patients with DME. Methods. - In this prospective observational study of type 1 (n = 4) and type 2 (n = 18) diabetic patients with DME, OCT scans, capillary blood glucose, and systolic and diastolic blood pressure measurements were performed at 9 a.m., 12 a.m., 3 p.m., 6 p.m. and again at 9 a.m. the day after. At the same time, the study protocol included simultaneous ambulatory blood pressure and glucose monitoring over a 24-h period. Hypoglycaemic episodes, defined as glucose values <60 mg/dL, were also recorded. Results. - CMT decreased consistently between 9 a.m. and 6 p.m. in 10 patients (from 374 +/- 82 mu m to 337 +/- 72 mu m; P = 0.01) and increased or remained steady in 12 others (from 383 +/- 136 mu m to 390 +/- 149 mu m; P = 0.58), with a significant difference in CMT absolute change between the two groups (P < 0.001). In the. study population as a whole, the lower the mean diurnal blood glucose, the smaller the decrease in CMT during the day (P = 0.027). Also, eight (67%) of the 12 patients with a flat CMT profile experienced a diurnal hypoglycaemic event whereas none of those with a CMT decrease had hypoglycaemia (P = 0.002). Conclusion. - Hypoglycaemic events may explain the lack of diurnal CMT decrease in diabetic patients with DME. However, further studies need to be conducted to evaluate whether having no diurnal CMT decrease is associated with a poorer visual prognosis and whether it can be modified by better glucose control. (C) 2012 Elsevier Masson SAS. All rights reserved.