[visionlist] Teller Acuity Cards

Fri Feb 14 12:03:01 -04 2020

Dear Gislin, Meindert, and Christopher,

>From the photos, this looks like an awful test.  "If" the luminance artifact were systematically related to the acuity level, then it "might" be a test for the joint effects of CS and VA on vision. However, such a test would require an enormous amount of research to determine whether this is actually true, and if so what to make of it clinically.  If a patient doesn't see the pattern on a card, is it because his/her VA is poor or his/her CS is poor?

Every so often somebody tries to create an "ecologically valid" test by taking acuity or contrast patterns and making them in the shapes of faces or other recognizable stimuli.  However, I really doubt the value of this effort, because stimuli that are barely detectable just don't look like the objects that are portrayed. Try it sometime: make a schematic face, then reduce its contrast until it is truly barely visible: does it look like a face?  Or do the same with a duck cutout acuity target. When you can barely detect it, does it really look like  duck? I am not asking whether you can tell the difference between a duck and a Volkswagen beetle, I'm asking whether it actually looks like a duck.

For these reasons, I greatly doubt that these knockoff acuity cards will turn out to be useful in the clinic or in the lab.

The cards are expensive because it is really, really hard to make the current Teller cards so the grating really does match the surrounding field perfectly. The original VisTech gratings were VERY hard to make (I was in the Teller lab when VisTech was working on them), and in the end, several of the cards were far from perfect. The Stereo Vision cards were REALLY bad, and are mercifully not still sold.  It took Precision Vision  many years of hard effort and a ton of financial investment to make what are now a pretty darn good set of cards. And I am not at all convinced that "tapering" the edges would be possible to do without introducing a much more serious artifact than any tiny artifacts at edges that now exist.

So either you pay for the real cards and save yourself the headache of making them yourself, or else you duplicate the efforts of the professional master printers and hope you will finally succeed, or else you settle for a bad set of cards.

I'm sorry to be so discouraging: I know it looks easy to make your own, and I know they cost a lot.

Best wishes to all,

Angela

Angela M. Brown, PhD
Professor
The Ohio State University
College of Optometry
338 West 10th Ave
Columbus, OH, 43210, USA
614-292-4423
brown.112 at osu.edu

-----Original Message-----
From: visionlist [mailto:visionlist-bounces at visionscience.com] On Behalf Of Gislin Dagnelie
Sent: Thursday, February 13, 2020 7:52 PM
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
--
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://urldefense.com/v3/__http://ultralowvisionlabjhu.net/__;!!KGKeukY!hTXS4Ain5i9G-SvBxritkW8Euq5uLkMQe7pEZU1M9KNoRpRpQKwJEu5K52MA16i2WyQ$ 
USA			        e-mail: gislin at jhu.edu

On 13 Feb 2020 at 13:24, Christopher Taylor <christopher.taylor at gmail.com> 
wrote:

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?

Best,

C

On Thu, Feb 13, 2020 at 9:36 AM Meindert de Vries <meindertdevries at visio.org>
wrote:

> 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
our
> 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*
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