Impact of diabetes on glaucoma screening using frequency-doubling perimetry

To determine whether diabetes is a potential source of abnormal test results in glaucoma screening by use of frequency-doubling perimetry.

Observational case series.

Twenty-five patients with diabetes and 25 nondiabetic normal controls, all without cataract or glaucoma.

Frequency-doubling perimetry using the C-20-5 screening mode was performed in 1 randomly selected eye of each participant. Abnormal test results were immediately repeated to reduce artifacts caused by test inexperience. Frequency-doubling technology (FDT) results were assigned a numerical score between 0 (normal) and 87 (no stimuli detected).

Abnormal FDT test scores.

Overall, 7 of 25 (28%) patients with diabetes and 1 of 25 (4%) normal controls had an abnormal test; the 1 normal subject with an abnormal test was subsequently determined to have an abnormal glucose tolerance test. Four of the 7 patients with diabetes with abnormal FDT tests had no evidence of diabetic retinopathy on clinical examination. Patients with diabetes had higher test scores than normal controls (8.9+/-16.9 vs. 1.0+/-4.4, P = 0.028) and had longer test times than normal controls (66.4+/-35.5 seconds vs. 48.3+/-11.2 seconds, P = 0.019).

Frequency-doubling perimetry is abnormal in some patients with diabetes, including some patients with diabetes without clinical evidence of diabetic retinopathy. Abnormal FDT testing in diabetic eyes may not represent glaucomatous visual field loss. Diabetes may be a source of "false-positive" test results when this technology is used for glaucoma screening.