Temporal variation in diabetic macular edema measured by optical coherence tomography

To determine, by optical coherence tomography (OCT), whether there is a quantitative decrease in macular edema in diabetic subjects over the course of a day.

Observational case series.

Ten subjects with diabetic macular edema in 1 or both eyes.

Subjects were admitted to the hospital the evening before the study so that they would remain in the recumbent position until immediately before study measurements began. They then underwent 4 OCT measurements of macular thickness in both eyes, at 8:00 am, 11:00 am, 2:00 pm, and 5:00 pm. At each of these times, they also had refractions and visual acuity measurements using the Early Treatment Diabetic Retinopathy Study protocol. Macular thickness measurements determined by the Zeiss-Humphrey (Dublin, CA) optical coherence tomograph for each eye of each subject were plotted as a function of time.

Temporal changes in retinal thickness in each of the 9 macular sectors defined by the OCT protocol and in the entire macula of each eye, averaged from all 9 sectors; temporal changes in refractive error and visual acuity.

Four of the 10 subjects showed consistent decreases in macular thickness over the course of the day in 1 or more of the retinal sectors in 1 or both eyes. When macular thickness values were averaged over all 9 sectors for all subjects, both eyes showed consistent declines in mean thickness throughout the day. By t test, the 8 am value in each eye was significantly higher (P<0.0005) than any of the 3 later values, which did not differ significantly from each other. However, comparison of all 4 values by analysis of variance showed no significant differences. With the exception of 1 subject, there were no consistent changes in refractive error or in best-corrected visual acuity over the course of the study.

This study, using quantitative OCT determinations, seems to confirm the much earlier report by Sternberg et al, which used more subjective methods, that macular edema might vary over the day. That the 8 am value, obtained just after waking, was higher than the 3 later values (highly significant by 1 test) suggests that the decrease in macular thickness is most likely due to the shift from recumbent to upright body position, although our study protocol did not exclude other possible mechanisms. Although changes in macular thickness over the course of the day did not occur in all subjects, therapeutic studies for macular edema that use OCT as an outcome measure should control for time of day when these measurements are carried out.