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R. T. Chang, O. J. Knight, P. Ramulu, W. Shi, W. J. Feuer, D. L. Budenz; Combining Frequency Doubling Technology and GDx to Screen for Glaucoma. Invest. Ophthalmol. Vis. Sci. 2008;49(13):742.
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To determine the effectiveness of combining GDx ECC with Frequency Doubling Technology (FDT) in the diagnosis of glaucoma.
Participants were recruited prospectively from the Bascom Palmer Eye Institute. 70 eyes of 37 healthy controls by clinical exam and 50 eyes of 38 glaucoma patients with best-corrected visual acuity of 20/30 or better and no previous history of retinal disease were enrolled. The glaucoma patients ranged from mild to severe based on visual field criteria (no glaucoma suspects), with half of the eyes being categorized as mild. Patients were scanned by FDT and GDx without dilation.First, C-20-5 screening FDT was performed, with a reliable test defined as one or no false positives or fixation losses. An FDT abnormality was defined as any 2 squares with P < 5% that persisted upon repeat testing. Next, GDx ECC was obtained, with a minimum quality score of six. Normal Nerve Fiber Index (NFI) was defined as 1-30, with abnormal being above 30.
A logistic regression model using the more abnormal eye was created in which disease status was the dependent variable. NFI and FDT were both significant independent variables (p=0.001, 0.008 respectively). The model coefficients from the logistic regression (0.108, 1.97 respectively) were used to create a combined index with both tests, which increased the area under the ROC to 0.93 compared to 0.80 for FDT alone (p<0.001). FDT sensitivity and specificity were 87% and 73%. The combined index achieved sensitivity of 90%, specificity of 76%.
Currently, FDT is a common community screening tool. Use of a combined index created with test results from both FDT and GDx may increase the efficacy of screening. A useful feature of the combined index is the ability to select cut-points which improve specificity, an important consideration in a screening setting.
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