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| Explaining the Humphrey Matrix |
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Frequency doubling technology (or FDT) is a perimetry technique featured on the Humphrey FDT and Humphrey Matrix perimeters. FDT technology was first introduced in 1997 and since then has been widely reported in the scientific literature. Today it is widely used and accepted within the optometric and ophthalmic community in Australia and New Zealand. But how does it work?
Frequency Doubling Perimetry differs from Standard Automated Perimetry (SAP) mostly due to the FDT stimulus. The FDT stimulus consists of a low spatial frequency (less than 1 cycle per degree) sinusoidal grating that undergoes rapid counterphase flicker (i.e., light bars become dark and vice versa).
When this type of stimulus undergoes high temporal frequency counterphase flicker (ie greater than 15 Hz), the stimulus appears to have twice as many bars than are physically present, thus the name “frequency doubling” (see diagram below).
This stimulus illicits a response predominantly from retinal ganglion cells in the magnocellular pathway and it is thought that this targeted property reduces the redundancy in the visual system and leads to the FDT’s renowned glaucoma detecting capabilities. In fact FDT technology has been shown to pick up glaucomatous defects up to 4 years earlier than standard automated perimetry (SAP)1.
Apart from their obvious glaucoma detecting advantages, both instruments also feature screening tests in around 30 seconds and threshold tests in around 5 minutes per eye. And with no need for use in a darkened room, the Humphrey FDT and Humphrey Matrix are designed to fit in to any clinical situation.
Download a Humphrey Matrix (349kB) brochure
1. Medeiros, F. A et al. Frequency Doubling Technology Perimetry Abnormalities as Predictors of Glaucomatous Visual Field Loss. Am J Ophthalmol 2004;137(5):863-871
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Editor: Matthew Wensor
Product Manager
Ophthalmic Systems
Medical Business Group
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