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Can the specificity of the FDT for glaucoma be improved by confirming abnormal results?
J J Khong1, P N Dimitrov, J Rait
1Center for Eye Research, Australia University of Melbourne, Royal Victorian Eye and Ear Hospital, East Melbourne.
Purpose:
To determine whether the specificity of the frequency-doubling technology (FDT) perimeter in the screening mode for glaucoma can be improved by repeating abnormal screening results.
Methods:
The FDT perimeter was used in C-20-5 screening mode, and the right eye was tested first. After both eyes were tested, the screening was repeated in eyes with any abnormal visual field defects on FDT perimetry. The printouts were categorized as possible visual field abnormality (zero or one miss), probable visual field abnormality (two to four misses), and definite visual field abnormality (more than five misses). A clinical ophthalmologic examination was conducted on the day of the FDT perimetry screening.
Results:
Complete data were available for 223 people. The participants ranged in age from 23 to 91 years (mean, 68.5 years; standard deviation. 13.7 years), and 119 (53%) were women. The sensitivity of the FDT perimetry screening was 100%; both cases of glaucoma showed an abnormality on FDT perimetry both times. The specificity improved moderately from the first screening to the second screening. The specificity the first time was 62% (95% confidence interval, 53.1-71.2). The specificity the second time was 68.5% (95% confidence interval, 59.8-77.1). Improvement on FDT perimetry rescreening varied by the language spoken at home. Seven of the 19 non-English speakers without glaucoma improved on rescreening, compared with none of the 23 English speakers (P = 0.002). Seven of the 25 right eyes with FDT perimetry abnormalities both times and no glaucoma had no other detectable diseases. Three of 24 left eyes with FDT perimetry abnormalities both times and no glaucoma had no other detectable diseases. Of the 85 patients who did not have glaucoma but had FDT perimetry abnormalities both times, only one did not have some other detectable disease.
Discussion:
In summary, the sensitivity for glaucoma of the C-20-5 screening mode is excellent, but a paradigm for screening with the FDT perimeter to improve the overall specificity for glaucoma still must be developed.