Effect of Diabetes Control on Rates of Structural and Functional Loss in Patients with Glaucoma

Purpose: To investigate the association between levels of diabetes mellitus (DM) control and rates of visual field and retinal nerve fiber layer (RNFL) loss over time in glaucoma.

Design: Retrospective cohort study.

Participants: A total of 351 eyes of 222 patients with type 2 DM with concomitant primary open-angle glaucoma (POAG) or suspected glaucoma extracted from the Duke Glaucoma Registry.

Methods: All patients had at least 2 reliable standard automated perimetry (SAP) tests, 2 spectral domain OCT (SD-OCT) tests, and 2 glycated hemoglobin (HbA1c) measures over time with a minimum follow-up of 6 months. Values of HbA1c were summarized for each patient as mean, peak, and fluctuation across time. Multivariable linear mixed models were used to estimate the effect of HbA1c on rates of change in SAP mean deviation (MD) and OCT RNFL thickness loss over time while adjusting for various confounding factors.

Main outcome measures: Rates of change in MD and RNFL thickness over time.

Results: Subjects had a mean baseline age of 62.5 ± 10.2 years and follow-up time of 6.9 ± 5.1 years. Subjects had an average of 4.8 SAP tests (range, 2-28), 3.6 SD-OCT tests (range, 2-10), and 8.3 HbA1c tests (range, 2-21). Average HbA1c mean was 7.1% ± 1.1% (range, 5.4-11.7), peak HbA1c over time was 8.1% ± 2% (range, 5.5-15.6), and HbA1c fluctuation was 0.6% ± 0.6% (range, 0-4.4). Mean rate of SAP MD change was -0.09 ± 0.20 decibel/year (median -0.06 decibel/year; interquartile range -0.15 to 0.01 decibel/year), and mean rate of RNFL change was -0.83 ± 0.51 μm/year (median -0.76 μm/year; interquartile range -1.06 to 0.56 μm/year). After adjustment for confounding factors, mean, peak, and fluctuation in HbA1c levels were not significantly associated with rates of MD change over time (P = 0.994, P = 0.689, P = 0.920, respectively), nor were rates of change in RNFL loss over time (P = 0.805, P = 0.575, P = 0.770).

Conclusions: We did not find a significant association between diabetes control, as measured by levels of HbA1c, and rates of visual field or RNFL loss over time in individuals with glaucoma or suspected glaucoma.