To determine the variation in optical coherence tomography (OCT)–measured macular thickness in diabetic eyes without clinical edema and to investigate factors that might influence variation in macular thickness.

Retrospective, observational case series from a clinical practice.

Review of clinical charts and longitudinal OCT measurements of a consecutive series of 56 eyes of 56 patients with diabetes but no clinical macular edema. Measured variables include OCT central subfield mean thickness (CSMT), total macular volume (TMV), and logarithm of the minimum angle of resolution (logMAR) visual acuity.

Over a median follow-up of 17 months, interquartile range (IQR) (9, 23), the median variation in CSMT was 18 microns, IQR (11, 31), and the median variation in TMV was 0.09 mm³, IQR (0.06, 0.16). Variation in CSMT did not change significantly with increasing CSMT. Absolute, but not relative, variation in TMV increased with increasing baseline values (P = .0127 and P = .1538 for absolute variation and relative variation in TMV, respectively). The variation in CSMT and TMV did not vary with follow-up time and did not vary with age, gender, race, hypertension status, glycosylated hemoglobin, or retinopathy level.

Variation in CSMT and TMV in diabetic eyes without DME over intervals up to 17 months is no greater than OCT measurement variability in eyes without and with DME. A change in the OCT-measured macular thickness greater than 10% of the baseline thickness is likely to represent a true change in the macular thickness and not OCT measurement variability, diurnal variation, or variability occurring over longer time scales.