Diurnal variation in clinically significant diabetic macular edema measured by the Stratus OCT

To investigate diurnal variation in clinically significant macular edema (CSME) using the Stratus OCT (Carl Zeiss Meditec).

Fifteen eyes of 15 diabetic patients with CSME and 10 healthy subjects (controls) underwent four optical coherence tomography (OCT) measurements of macular thickness with the fast macular thickness mapping protocol of the Stratus OCT at 9 am, 12 pm, 3 pm, and 6 pm. Early Treatment Diabetic Retinopathy Study visual acuity and refraction data were also collected at each time. Retinal thickness measurements from each of the nine macular Early Treatment Diabetic Retinopathy Study areas of the retina map, visual acuity, and refraction were plotted over time.

Mean retinal thickness remained unchanged in all retinal sectors over the course of the day for the controls and the 6 diabetic patients with a baseline foveal thickness of <300 mum, and it significantly decreased in 7 of the 9 retinal sectors for the 9 diabetic patients with a baseline foveal thickness of > or =300 microm (ANOVA model for repeated measures). In these patients, the mean initial foveal thickening +/- SD of 211 +/- 104 microm was reduced by an average of 6.1%, 15.2%, and 21.2% at 12 pm, 3 pm, and 6 pm, respectively. Two of these nine patients also had an increase in visual acuity without change in refraction. There were no changes in refractive errors over the course of the study in the two groups. A positive correlation between initial central thickening and decrease in thickness was found (r = 0.732; P = 0.002).

This study suggests that macular thickening, as measured by the Stratus OCT, may spontaneously decrease in some patients with more severe CSME over the course of the day, and it confirms previous findings. However, in our study, the entity of this decline was relatively small and not relevant from a clinical standpoint.