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Dual frequency perimetry
Last reviewed: 06.07.2025
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Dual Frequency Perimetry (DFP) technology (Welch Allyn, Skaneateles, NY, and Humphrey Systems, Dublin, CA) is used for effective early visual field assessment and detection of glaucomatous visual field changes. This small, tabletop device is compact and easy to use in the office or on-site.
[ When is dual frequency perimetry used?
Dual frequency perimetry is an important test for general glaucoma screening because it is rapid, inexpensive, easy to perform, and has high sensitivity and specificity. Dual frequency perimetry is effective in detecting visual field defects in glaucoma, as well as in detecting signs of neurological disease, including anterior ischemic optic neuropathy, pseudotumor cerebri, and compressive optic neuropathies.
How Dual Frequency Perimetry Works
The phenomenon of frequency double imaging is obtained by rapid spatial blinking of a grating of patterns of white and black stripes with a low spatial frequency, which creates a sensation of doubling of the actual elements visible to the patient. The data obtained suggest that large ganglion cells (M-cells) are selectively killed, which affects the large-cell layers of the lateral geniculate body more than other cell types in glaucoma. A small subpopulation of ganglion cells gives a nonlinear response to frequency-doubling stimuli supplied by dual frequency perimetry. The device, compared with the Humphrey Field Analyzer standard achromatic perimetry as the "gold standard", detects glaucomatous visual field lesions with more than 90% sensitivity and specificity.
Restrictions
The current version of dual frequency perimetry in the N-30 glaucoma testing program presents 19 sites, each covering 10 degrees of the visual arc. Each site covers a larger area, and the number of sites is significantly smaller compared to the standard 24-2 Humphrey visual field testing program. The standard 24-2 program tests 54 sites, each covering 4 degrees of the arc. Newer versions of dual frequency perimetry record more sites, each covering a smaller visual arc to improve spatial resolution. In fact, the dynamic range of dual frequency perimetry is greater than that of the “gold standard” achromatic perimetry HFA.