Comparison of Frequency Doubling Technology and Standard Automated Perimetry for Detecting Glaucomatous Visual Field Progression. A Longitudinal Prospective Study.

Abstract

Abstract: : Purpose: To determine whether Frequency Doubling Technology (FDT) perimetry detects visual field progression earlier than Standard Automated Perimetry (SAP). Methods: Our sample contained one eye of 71 patients with open–angle glaucoma tested every six months with both FDT (N–30 programme) and SAP (full threshold 24–2 programme of the Humphrey Field Analyser) for a median duration of 4 years with a median of 9 examinations with each technique. Visual field change was determined using the glaucoma change probability analysis based on total deviation. We used 15 different criteria for progression but ensured that for each the number of locations required to be flagged with either technique was approximately equal on a percentage basis. The least conservative criterion was requirement of 1 location on FDT and 3 on SAP to be confirmed in 2 of 3 consecutive tests, while the most conservative was 3 locations on FDT and 10 on SAP to be confirmed in 3 consecutive tests. We computed the number of patients who progressed with each technique and criterion, and performed a difference in time to progression analysis in those patients who progressed with both techniques (when n > 3). Results: At baseline, the mean age was 63.9 ± 11.1 years while the FDT and SAP Mean Deviation values were –4.39 ± 4.19 dB and –6.09 ± 4.54 dB respectively. With the least conservative criterion, 45% and 25% of patients progressed with FDT and SAP respectively, with 14% progressing with both. For each criterion, more patients progressed with FDT compared to SAP. The number of patients progressing with both techniques was small, indicating that FDT and SAP predominantly identify different subsets of patients. Only 3 criteria yielded > 4 patients progressing with both techniques. In these cases FDT identified progression earlier in 6 of 7, 6 of 10, and 4 of 4 patients respectively. Conclusions: Progression rates with FDT appeared to be higher compared to SAP. These findings could be due to incomplete equivalence in the number of locations required to be flagged by each technique. However, in those patients who were classified as progressing with both FDT and SAP, FDT appeared to detect progression earlier.

Keywords: visual fields • perimetry • clinical research methodology