| Identifier |
frequency_doubling_technology_perimetry_lee |
| Title |
Frequency Doubling Technology Perimetry |
| Creator |
Andrew G. Lee, MD; Lauren Nakhleh |
| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (LN) Class of 2023, Baylor College of Medicine, Houston, Texas |
| Subject |
FDT; Visual Field Loss; Automated Perimetry Screen |
| Description |
Summary: Frequency Doubling Technology (FDT): an easily portable, fast, and inexpensive instrument used to detect visual field loss • similar to Humphrey visual field, but uses frequency doubling to create an illusion • not used in neuro-ophthalmology, but reasonable as an automated perimetry screen. |
| Transcript |
So today I'm going to be talking about FDT, which is frequency doubling technology. And so FDT in neuro-ophthalmology is mostly about knowing what it is, even though we don't usually use it in neuro-ophthalmology. And so, your typical FDT printout is similar to what a Humphrey visual field printout looks like on the grayscale. But instead of having threshold perimetry, as in standard automated perimetry the Humphrey visual field where you're using a stair stepping strategy to increase and decrease the decibel stimulus of light to determine threshold and probability of abnormality compared to normal controls, in FDT we rely upon a different technology. And that is frequency doubling. So, when you have a vertical sine grading like these three bars, if we change the frequency, moving from low spatial frequency to high, we can create an illusion called the frequency doubling illusion where the three bars will suddenly appear to be six bars. And that's similar to what happens when you're watching a movie. A series of still frames can be sped up by increasing the frequency that will give the appearance that it's moving even though it's really stationary. And it's an illusion. A frequency doubling illusion because it's a real stimulus but you're misinterpreting that stimulus as six bars, a doubling of the three bars, even though it's really only three. And so, in a patient who has FDT you're taking advantage of FDI, by changing the frequency we can induce a doubling illusion. And so, if we're testing this square here analogous to testing a spot-on Humphrey visual field the patient will see six of these grates even though it's really just a combination of two different sets of three that are counter facing. And that flicker is what's creating the illusion of six. So even though there's only three they see six. And that is frequency doubling technology. It takes advantage of the intrinsic characteristics of the different cells that are interpreting the information. It used to be thought that it was just the type of cell, the MY cell in the magnocellular layer, however we know there's probably some processing in the cortex layer. It doesn't matter because the technology is the same. We're using a frequency doubling illusion in frequency doubling technology called FDT to test visual field. It's not the same as, and probably not as good as, Humphrey visual field and probably can't be used for neuro-opthalmology things like we're using it for. But it's reasonable to have this as an automated perimetry screen if you have nothing else. So, if it's completely normal, that's usually a good sign that the field really is normal. If it's abnormal, there are all sorts of things that can cause artifacts in frequency doubling technology. And so, we're going to recommend a confirmatory Humphrey visual field. And in general, the papers, not for glaucoma but for neuro-op, suggests that we really can't use FDT reliably for neuro-ophthalmology diseases. And I would refer to you the American Academy of Ophthalmology consensus statement publishing ophthalmology about visual fields and the studies of FDT and glaucoma versus standard automated perimetry. You need to know about it because it creates problems in neuro-op because a lot of general ophthalmologists and optometrists have FDT because it's portable, it's fast and it's relatively inexpensive. And so, it produces a lot of referrals for patients who have visual field defects that may or may not be neuro ophthalmic. And in those patients, were always going to go back to standard automated parameters to confirm the finding and also to make sure it's not an artifact. So even though I personally don't use FDT, every ophthalmologist needs to know a little bit about FDT. |
| Date |
2021-04 |
| Language |
eng |
| Format |
video/mp4 |
| Type |
Image/MovingImage |
| Collection |
Neuro-Ophthalmology Virtual Education Library: Andrew G. Lee Collection: https://novel.utah.edu/Lee/ |
| Publisher |
North American Neuro-Ophthalmology Society |
| Holding Institution |
Spencer S. Eccles Health Sciences Library, University of Utah |
| Rights Management |
Copyright 2019. For further information regarding the rights to this collection, please visit: https://NOVEL.utah.edu/about/copyright |
| ARK |
ark:/87278/s60922zr |
| Setname |
ehsl_novel_lee |
| ID |
1680604 |
| Reference URL |
https://collections.lib.utah.edu/ark:/87278/s60922zr |
