[visionlist] Teller Acuity Cards

Fri Feb 14 09:54:28 -04 2020

Davida Teller, Velma Dobson and their colleagues developed the Teller Acuity Cards to test resolution acuity.  To do that, the target must ‘disappear’ when the white and black components of the stimulus can no longer be resolved.  This requires that the mean luminance of the target area is perfectly matched to the mean luminance of the rest of the card.  This is hard to do and makes the printing process difficult and more expensive (including visual inspection of each individual card from extended distance to confirm that there are no visible artifacts beyond the resolution limit).  Vanishing optotype tests, such as the Cardiff Cards, use the same principle.  Even though the vanishing optotype has a shape that can be recognized, the shape is defined by a single black & white paired outline that ‘disappears’  to mean luminance when the components can no longer be resolved.

A test that is constructed to use the forced-choice preferential looking principle (is the target on the left or right of the card?) is critically dependent on having no visible artifact to indicate where the target is once the resolution limit is passed.  This new test appears to have a difference in mean luminance between the target area and background, and therefore it is not a test of resolution acuity.  It then becomes a test of detection acuity (can the target be detected using the difference in luminance?), similar to asking whether we can detect a star against a dark sky.  Based on these photographs, it seems very likely that these large targets can be detected easily at the viewing distance that this test would be performed, making it a poor test of detection acuity.

Any new acuity test should be provided with testing norms that have demonstrated its validity for the population being tested.  One easy confirmation of validity in the absence of normative data is to determine the viewing distance at which an observer can no longer perform the task.  If the observer has 20/20 (6/6) acuity, is the card labeled approximately equivalent to 20/20 at the observer's performance limit at the recommended testing distance?   Is the card labeled approximately equivalent to 20/40 (6/12) at the observer's performance limit at twice that viewing distance etc.  I am guessing that a typical observer will still be able to do this test at the end of a long corridor and, therefore, that the test is not valid.  (Candy, Mishoulam, Nosovsky & Dobson; IOVS, 2011)

I am doing my best to channel Davida and Velma!

   Rowan

.........................................................................................................................
T. Rowan Candy,
Executive Associate Dean for Academic Affairs,
Professor of Optometry and Vision Science,
Adjunct Professor of Psychological & Brain Sciences
Neuroscience and Cognitive Science Programs
Indiana University

Phone: (812) 855-9340
http://www.opt.indiana.edu/people/faculty/candy/index.html

> On Feb 13, 2020, at 7:52 PM, Gislin Dagnelie <gislin at lions.med.jhu.edu> wrote:
> 
> 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    http://ultralowvisionlabjhu.net/
> 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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>> 
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>> 
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>> 
>> 
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>> 
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>> 
>> 
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