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Frequency doubling technique in patients with ocular hypertension and glaucoma: correlation with octopus perimeter
M Iester1, A Mermoud, C Schnyder
1Hopital Ophtalmique Jules Gonin, Lausanne, Switzerland.
Purpose:
To ascertain whether frequency doubling technique (FDT) (Welch-Allyn, Skaneateles, NY; Zeiss-Humphrey, San Leandro, CA) indices provide results comparable with those of standard Octopus threshold perimeters (Interzeag AG, CH-8952 Schlieren, CH) in patients with glaucoma and in patients suspected of having ocular hypertension, glaucoma, or both.
Design:
A comparative, consecutive, case series.
Participants:
Thirty-nine glaucomatous patients and 41 patients with ocular hypertension or suspected glaucoma were recruited consecutively.
Methods:
The visual field of the study participants were assessed by FDT program C-20 full threshold and Octopus program dG1X. Only one eye of each participant was selected randomly. Pearson's r correlation coefficient was calculated among the FDT and Octopus indices.
Main Outcome Measures:
Using Octopus perimeter, mean defect (MD), mean sensitivity (MS), loss variance (LV), and corrected loss variance (CLV) were calculated and used for correlation. For the FDT, mean deviation (FDT-MD) and pattern standard deviation (FDT-PSD) were calculated and used for correlation. Also, the time required to perform the visual field test was considered.
Results:
In the entire population, a statistically significant correlation (Pearson's r, P<0.001) was found between FDT-MD and both MS (0.77) and MD (-0.80) and between FDT-PSD and both LV (0.50) and CLV (0.45). When the glaucoma group was considered alone, similar significant correlation was found between the indices. In the suspected ocular hypertension and glaucoma suspect group, no significant correlation was found. A significant (P<0.001) difference was found between FDT and Octopus for the time needed to perform the visual field test.
Conclusions:
This new technique could be used both to screen populations and to observe glaucomatous visual field progression in early and moderate stages. The FDT is a faster way to analyze the visual field and captures threshold values for each point, but it is important to remember that this is a new technique and its limits are still unknown.