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Dual frequency perimetry
Last reviewed: 25.06.2018
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Dual Frequency Perimetry (WELCH) technology (Welch Allyn, Skaneateles, NY, and Humphrey Systems, Dublin, CA) serves to provide an effective early assessment of the visual fields and the detection of glaucomatous changes in the visual fields. This small desktop device is compact, it can be easily used in the office or when traveling to places.
[When a double frequency perimetry
Dual frequency perimetry is an important study for the general screening of glaucoma, because it is fast, inexpensive, easy to perform, with high sensitivity and specificity. The use of double frequency perimetry is effective for detecting visual field defects in glaucoma, as well as for detecting signs of neurological diseases, including anterior ischemic optic neuropathy, brain pseudotumor, and compression optic neuropathies.
How the double frequency perimetry works
The phenomenon of frequency double image is obtained with rapid spatial blinking of the pattern of patterns from white and black bands with low spatial frequency, which creates a feeling of doubling the actual visible elements of the patient. According to the data received, it is assumed that large ganglion cells (M-cells) are selectively killed, which affects the large-cell layers of the lateral geniculate body more than other types of cells in glaucoma. A small subpopulation of ganglion cells gives a nonlinear response to the frequency-doubling stimuli supplied by the double frequency perimetry. The instrument, compared to the Humphrey Field Analyzer with standard achromatic perimetry as a "gold standard" - determines the glaucomatous lesions of the visual fields with more than 90% sensitivity and specificity.
Restrictions
In the current version of the double frequency perimetry, in the N-30 testing program for glaucoma, 19 sites are plotted, in each 10 degrees of the visual arch. Each site covers a large area, and the number of sites is significantly smaller compared to the standard 24-2 Humphrey field of vision study . In the standard program 24-2, 54 sites are examined, each of which covers the 4 degrees of the arch. In newer versions of the double frequency perimeter, more sites are recorded, to improve spatial resolution, each of them is covered with a smaller visual arch. In fact, the dynamic range of the double frequency perimetry is greater than in the "gold standard" of the achromatic perimetry of HFA.