Diurnal Variation in Retinal Thickening Measurement by Optical Coherence Tomography in Center-Involved Diabetic Macular Edema

Abstract

Objective: To evaluate diurnal variation in Optical Coherence Tomography (OCT) measured retinal thickness in patients with center-involved diabetic macular edema (DME). Methods: Serial OCT3 measurements were performed in 156 eyes of 96 subjects with clinically-diagnosed DME and OCT central subfield retinal thickness ≥225 microns at 8 a.m. Central subfield thickness was measured from OCT3 retinal thickness maps at 6 time points over a single day between 8 a.m. and 4 p.m. A change in central subfield thickening (observed thickness minus mean normal thickness) of at least 25% and of at least 50 microns at two consecutive time points or between 8 a.m. and 4 p.m. was considered to have met the composite outcome threshold. Results: At 8 a.m., the mean central subfield thickness was 368 microns and the mean visual acuity was 66 letters (approximately 20/50). The mean change in relative central subfield retinal thickening between 8 a.m. and 4 p.m. was a decrease of 6% (95% CI -9% to -3%) and the mean absolute change was a decrease of 13 microns (95% CI -17 to -8). The absolute change was significantly greater in retinas that were thicker at 8 a.m. (P <0.001) but the relative change was not (P=0.14). The composite threshold of reduction in central subfield thickening (as defined above) was observed in 5 eyes of 4 subjects (3% of eyes, 95% CI, 1% to 8%) while 2 eyes of 2 subjects (1%, 95% CI, 0% to 5%) had an increase in central subfield thickening of this same magnitude. The maximum decrease was observed at 4 p.m. in all 5 eyes. Conclusions: Although on average there are slight decreases in retinal thickening during the day, most eyes with DME have little meaningful change in OCT central subfield thickening between 8 a.m. and 4 p.m.