Correlation between frequency doubling technology perimetry and temporal frequency characteristics in early glaucoma

To assess the effectiveness of the temporal frequency characteristics (TFC) as an indicator of visual damage in patients with early open-angle glaucoma, TFC obtained from VEPs elicited by a pseudorandom binary sequence (PRBS) stimulus was compared with the frequency doubling technology (FDT) thresholds. Cross power spectrum between the PRBS stimulus as the input and the PRBS-VEPs as the output was calculated, and was used as the TFC. The normalized amplitude of the TFC at 2-4, 6-8, 10-12, 14-16, 18-20, 22-24, 26-28, and 30-32 Hz was calculated, and a coefficient of correlation between these values and the FDT thresholds was determined. The coefficients of correlation between the FDT thresholds and the TFC at 18-20 Hz for the central, 10degrees, 20degrees, and 30degrees were r = 0.03,0.31,0.2 1, and 0.16, respectively in non-glaucomatous normal control eyes, and those for the same regions of eyes with early glaucoma were r = 0.66, 0.46, 0.38, and 0.35, respectively. The coefficients of correlation between the FDT thresholds and TFC at temporal frequencies were relatively high at 18-20 and 26-32 Hz. The time required to obtain the PRBS-VEP data was approximately the same as that for the FDT thresholds. The strong correlation between the two tests indicates that the FDT values and the high temporal frequency segments of the TFC may be useful as a preliminary indicator of visual damage in patients with early open-angle glaucoma. In addition, the strong correlation suggests that there was a preferential damage to the magnocellular system in glaucomatous eyes.