[visionlist] Teller Acuity Cards

Fri Feb 14 11:06:10 -04 2020

For me the million dollar question is rather similar to Meindert's point - why would you incorporate variable contours into a preferential looking (and by nature detection-based) test? I just don't understand the need to change the contour between cards... I mean, maybe you might want to use a more visually interesting contour to maintain interest, but why use several different ones that don't appear to take up the same surface area and don't blur to the same contour a la Lea Symbols? And of course if for some reason you did want to use this test over something like Low Vision Kay Pictures and encourage picture naming alongside looking, there's then the question of whether each picture is equally visible for identification at a given spatial frequency. This is why Kay's did a number of studies when updating the images used in their test.

Are there any papers or normative data for this new test? What is it called?

Best wishes
Marianne

Dr Marianne Coleman
Research Fellow
Digital Health :: Maternal, Child and Family Health
University of Surrey - Celebrating 50 years in Guildford
Tel: +44 (0) 1483 686714  
Email: m.coleman at surrey.ac.uk 
Web: surrey.ac.uk
Kate Granger Building, University of Surrey, Guildford, Surrey, GU2 7YH, UK

-----Original Message-----
From: visionlist [mailto:visionlist-bounces at visionscience.com] On Behalf Of Jones, Pete
Sent: 14 February 2020 09:36
To: gislin at jhu.edu; 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

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.. 

Best, pete

Pete R Jones, PhD
Post-doctoral Research Associate
UCL Institute of Ophthalmology
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-----Original Message-----
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
--
Gislin Dagnelie, Ph.D.
Associate Professor of Ophthalmology
JHU Lions Vision Research & Rehab Center Johns Hopkins Hospital, Wilmer Woods 358
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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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