While diabetes is often considered a risk factor for glaucoma, a new study from Duke University found no significant association between diabetes control—as measured by HbA1c levels—and rates of visual field and retinal nerve fiber layer (RNFL) loss over time in individuals with glaucoma or glaucoma suspects.

The study reviewed data from the Duke Glaucoma Registry and included 351 eyes of 22 patients with concomitant Type II diabetes with primary open-angle glaucoma (POAG) or who were glaucoma suspects.

All patients had at least two reliable standard automated perimetry tests, two spectral domain OCT (SD-OCT) tests, and two glycated HbA1c measures with a minimum follow-up of six months.

HbA1c values were summarized for each patient as mean, peak and fluctuation across time. The researchers estimated the effect of HbA1c on rates of change based on standard automated perimetery and OCT RNFL thickness loss findings over time. Patients were about 63 years old, were followed up at approximately seven years, and underwent, on average, five perimetry tests, four SD-OCT tests and eight HbA1c tests.

The average HbA1c was 7.1±1.1%, peak HbA1c over time was 8.1±2% and HbA1c fluctuation was 0.6±0.6%.

Additionally, the mean rate of visual field mean deviation (MD) change was

-0.15±0.36 dB/year, and the mean rate of RNFL change was -0.76±0.45μm/year.

After adjusting for confounding factors, the researchers found no statistically significant association between mean, peak or fluctuation in HbA1c levels, rates of MD change over time or RNFL loss over time.