[visionlist] Teller Acuity Cards

Ruth Hamilton Ruth.Hamilton at glasgow.ac.uk
Mon Feb 17 12:59:00 -04 2020

Dear Rowan
Further to your point, our team made some systematic measurements of target vs background luminance for TAC, as well as Keeler Cards for Infants, Lea Paddles and Cardiff Acuity Cards, and also for a digital test (ipad, Peekaboo). The data are currently being peer reviewed, but we found luminance (and colour) mismatches of differing degrees for all the card-based tests. We also found some improbably good psychophysical acuities (better than -0.300 logMAR) from some adults tested at 10 m with the card-based tests.
Best wishes

Dr R Hamilton PhD
Consultant Clinical Scientist, Paediatric Physiological Measurement
Royal Hospital for Children, Glasgow, UK
+44 141 452 4217

Secretary, BriSCEV

President, ISCEV

From: visionlist [mailto:visionlist-bounces at visionscience.com] On Behalf Of rcandy
Sent: 14 February 2020 13:54
To: Meindert de Vries
Cc: Margaret Woodhouse; gislin at jhu.edu; visionlist at visionscience.com
Subject: Re: [visionlist] Teller Acuity Cards

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!


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

On Feb 13, 2020, at 7:52 PM, Gislin Dagnelie <gislin at lions.med.jhu.edu<mailto: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

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    http://ultralowvisionlabjhu.net/
USA                                 e-mail: gislin at jhu.edu<mailto:gislin at jhu.edu>

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


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