APR 02, 2008
Frequency doubling technology (FDT) has been developed with glaucoma in mind, and its sensitivity is purported to be superior to standard methodology. The underlying theory is that FDT better stimulates M-cells, a small subpopulation of retinal ganglion cells that may be selectively impaired in glaucoma and other optic neuropathies, such as optic neuritis. A second generation FDT system called Humphrey Matrix Perimeter has recently become available.
A study compared use of Humphrey Matrix 24-2 perimetry (Carl Zeiss Meditec, Inc., Dublin, Calif.) to the standard Humphrey Field Analyzer using Swedish Interactive Threshold Algorithm (SITA) program 24-2 (Carl Zeiss Meditec) in 93 patients with anterior visual pathway disease. Concordance was better for total deviation plots than for pattern deviation. Sensitivity and specificity values were about the same with these two systems. The study's authors rated the two systems as equal.
A similar study conducted by many of the same authors and published in the same journal issue compared the performance of the two devices in 32 patients with homonymous hemianopsias and 50 control subjects. Although the sensitivity of the Matrix for detecting hemianopsias by total deviation was only 59%, versus 75% for standard perimetry, this difference was not statistically significant due to the study's small number of subjects. For pattern deviation, the Matrix's sensitivity for detecting hemianopsias was about the same as standard perimetry (86% versus 84%). The authors concluded that testing with the Matrix led to obscuration of some homonymous defects because its larger stimulus size caused some stimulus scatter effects.