[visionlist] Teller Acuity Cards
p.r.jones at ucl.ac.uk
Fri Feb 14 05:36:00 -04 2020
Well put Gislin.
Though I wonder if (1) is due to the camera, or subsequent image-compression? Easy enough to check by standing far away and seeing if the luminance difference is visible to the naked eye.
I find it hard to believe that the manufacturers could make such a fundamental error. Though I note that --- presumably due to fading/discoloration over time --- a similar thing has happened to an old set of Keeler Acuity Cards that I have (cards which were presumably well calibrated when they came off the printing press).
With respect to (2), it's strange that edge ramping still hasn't caught on among printed cards, but yes this criticism also applies to Teller Cards -- the edges of which are absolutely visible even when the gratings cannot be resolved. I can only assume that this isn't a problem in practice because most infants aren't so motivated to 'cheat'. Acuity would absolutely be over-estimated in adults with either product, which seems... unfortunate.
Ultimately I'd say it's an empirical question whether these new cards work sufficiently well for their intended use. Would be nice to see some data. But yeah, I'd not be optimistic myself..
Pete R Jones, PhD
Post-doctoral Research Associate
UCL Institute of Ophthalmology
11-43 Bath Street, London. EC1V 9EL
Tel 020 7608 6819 Email p.r.jones at ucl.ac.uk
The Child Vision Lab
From: visionlist <visionlist-bounces at visionscience.com> On Behalf Of Gislin Dagnelie
Sent: 14 February 2020 00:52
To: Meindert de Vries <meindertdevries at visio.org>; Christopher Taylor <christopher.taylor at gmail.com>
Cc: visionlist at visionscience.com
Subject: Re: [visionlist] Teller Acuity Cards
Chris and Meindert,
I definitely agree with Meindert's objection to the cards he presents.
One thing that is critically important about any card that intends to assess visual acuity (high-spatial frequency resolution, if you will) through high-resolution texture filling a contour is that:
1) the average luminance inside the contour is equal to that outside it, and
2) the edges of the contour are filtered, preferably with a raised cosine of a spatial frequency equal to the fundamental of the texture inside the contour.
Unless Meindert's photographic rendition is grossly misrepresenting the actual hues and greyscale levels on the new cards, the cards do not meet the first
requirement: In all cases the average luminance inside the contour is lower than outside.
The cards definitely do not meet the second requirement: there is no filtering around the contour edges
So I have to agree with Meindert that there are serious problems with these cards.
Note, BTW, that the Teller cards do not use filtering around the outside of the contour either, but this may be less important because of the square contour of each pattern: black and white bars are equal in area. Still this may lead to an overestimation of acuity compared to an unconstrained grating
So while I agree with Chris that there is room for valid alternatives to the Teller cards, the ones shown here do not appear to meet the minimum requirements for such an alternative.
But maybe I'm missing something?
Gislin Dagnelie, Ph.D.
Associate Professor of Ophthalmology
JHU Lions Vision Research & Rehab Center Johns Hopkins Hospital, Wilmer Woods 358
1800 Orleans St
Baltimore, MD 21287-0023 https://eur01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fultralowvisionlabjhu.net%2F&data=02%7C01%7C%7Cfc9df8eb271245f228b708d7b0ede831%7C1faf88fea9984c5b93c9210a11d9a5c2%7C0%7C1%7C637172408170893166&sdata=JboE7yVCQ9YBL0k%2FW3Ys%2BqlCoQBv0peVQhLvV0bm4to%3D&reserved=0
USA e-mail: gislin at jhu.edu
On 13 Feb 2020 at 13:24, Christopher Taylor <christopher.taylor at gmail.com>
Why do you believe this test has a fundamental error versus TAC testing? It
is a different test, no more, no less.
To play devil's advocate, one could claim that Teller Acuity Cards lack
ecological validity because they do not present contours and objects, which
are more important to the visual system during daily living than sinusoidal
or square-wave gratings. That said performance on this test and TAC ought
to correlate and if this new test has other benefits (e.g, faster/easier to
administer, cheaper and more available to purchase, and so on...) and has
appropriate age-norms for the population being screened then might it not
be an advance on traditional TAC testing?
On Thu, Feb 13, 2020 at 9:36 AM Meindert de Vries <meindertdevries at visio.org>
> Dear members ,
> Since 1992 I work for Visio, an institution the helps visually impaired
> people. We have always been using the Teller Acuity Cards to determine
> the visual acuity in children.
> A new test has been presented on the scene, proposing to replace the
> Teller Acuity cards, because the TAC are expensive and sometime difficult
> to get. I enclose an example picture of the new cards.
> From my perspective and knowledge they have made some fundamental errors
> 1. The test seems ambiguous to me, because both object recognition
> part of our visual system as well as the much `lower" detection part of
> visual system is triggered by this stimulus
> 2. The spatial frequency content of these stimuli (checkerboard
> patterns with a distinctive contour) is in the Fourier domain essentially
> different from the TAC bar patterns without a contour; nevertheless the
> same cycl/cm are used.
> 3. In addition to point 2: I think that the contour is a much
> stronger stimulus than the checkerboards.
> Could anybody reflect on this ?
> Most kindley,
> *drs. M.J. de Vries 69024716001*
> *Koninklijke Visio Noord-West Nederland Revalidatie & Advies*
> Hettenheuvelweg 41-43 1101 BM Amsterdam
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