[visionlist] Teller Acuity Cards

Kenneth Knoblauch ken.knoblauch at inserm.fr
Fri Feb 14 15:48:53 -04 2020

Agreeing strongly with R. Candy's comments, it might also be of value
to mention the acuity cards developed by François Vital-Durand,
distributed by Tropique in which he attempted to extend the ingenious
ideas of Davida, Velma and their students to minimize the possibility of
edge artefacts (if there were any) and orientation anisotropies by using
circularly symmetric targets whose contrast was attenuated with distance
from the center, see attached image, which is not of sufficient
resolution to do it justice as it was grabbed from the web.  He spent a
great many days in a closet in the lab calibrating the grey level scales
with respect to the printer output with my photometer, and I working out
a best fit to the transfer function when he was developing these.



Kenneth Knoblauch
Inserm U1208
Stem-cell and Brain
Research Institute
18 avenue du Doyen Lépine
69500 Bron
tel: +33
(0)4 72 91 34 77
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On 2020-02-14 14:54, rcandy wrote:

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
> Indiana University
> Phone: (812) 855-9340
> 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
> 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
> 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
> 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
> But maybe I'm missing something?
> Gislin
> -- 
Gislin Dagnelie, Ph.D.
> Associate Professor of Ophthalmology
Lions Vision Research & Rehab Center
> Johns Hopkins Hospital, Wilmer
Woods 358
> 1800 Orleans St
> Baltimore, MD 21287-0023   
> 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
> 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
> 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
> *Revalidatieoogarts*
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