Teller Acuity Cards
are used to test visual acuity
in young children
and those with disabilities
who cannot be tested
with standard letter
or symbol acuity tests.
The stimulus
on a Teller Acuity Card
is a high contrast black
and white pattern
of stripes called a grating.
The gratings range
from very coarse to very fine,
in order to test visual acuity
from very low vision to normal.
Most rectangular cards
have a single grating
printed off to one side
of the center.
Printing the grating
to one side of the card
allows it to be presented either
on the left
or the right.
An additional card
has a grating nearly covering
one-half of the card.
This card
is called the low vision card.
The final card is a blank, gray card
without a grating.
Grating values are specified
by the width
of their black and white bars.
A single black and white pair
of bars is called a cycle.
Grating sizes are specified
by the number of black
and white cycles per centimeter.
The metric cycles per centimeter
is converted to visual acuity based
on the distance
of the Teller Acuity Card grating
from the patient,
and is specified as cycles
per degree.
The cycles per degree measure
is the appropriate specification
for grating acuity.
If necessary,
grating acuity can be converted
into conventional Snellen notation,
which may be more appropriate
for certain reporting.
Each Teller Acuity Card
has labels on the back
showing the grating size
in cycles per centimeter,
and the conversions to acuity based
on three test distances.
The labels on the back
of the card are placed
so the examiner has no information
about the right-left position
of the grating
from viewing the back of the card.
The primary principle
of a Teller Acuity Card
is that if a patient sees a grating
on the grey background,
she will look at the grating.
If the grating bars cannot be resolved
or seen by a patient,
the grating should match
the grey background perfectly,
mimicking the blank card.
The examiner's task
in testing Teller Acuity Cards
is to determine the finest grating
that the patient sees or detects.
This gives the patient's
visual acuity.
This requires testing a series
of gratings,
starting from relatively wide
and easily seen
to progressively finer gratings,
until the patient
no longer responds consistently.
The recommended clinical method
of testing is
for the examiner
to present a single grating
a sufficient number of times
to judge whether the patient
sees that grating.
As there are only two locations
where the grating can appear,
an examiner has a 50% chance
of guessing the correct location
without even watching the patient.
[no audible dialog]
This means that gratings
may need to be shown multiple times
if the patient's responses
are not definitive.
Typically, the patient's responses
will be definitive
when the grating is coarse
and above their acuity level.
However, a finer grating
that is more difficult
for the patient to see
may lead to more subtle responses
and require more presentations.
It is up to the examiner
to determine
how many presentations
she needs to be confident
of the patient's visual acuity.
[no audible dialog]
There is a small hole in the center
of the Teller Acuity Card
through which the examiner
or tester can view the patient
as they look at the gray card
and the grating.
The examiner can also view
the patient's responses
to the gratings
by looking over the top of the card.
[no audible dialog]
The examiner
is able to change the card position
to judge where the grating
is located, right or left,
based on the patient's
visual behaviors,
such as looking
towards the right or left,
or pointing or other behaviors.
The card is shown to the patient
by an examiner holding it
along the edges.
They should not be touching
the front surface of the card.
If the examiner uses fingers
to hold the card,
rather than the palm of the hand,
fingertips should not touch
the front,
except possibly within one inch
of the edge of the card.
The examiner shows the card
in one position
and makes a judgment as
to where the grating is
based on the patient's behavior.
In this case, the examiner
judges the grating to be on her left,
the patient's right.
The examiner
then rotates the card 180 degrees.
Now, if the infant's behavior
indicates seeing the grating,
the examiner should judge
the grating is on the infant's left.
The examiner
should not always rotate the card
180 degrees between presentations,
as some patients
may anticipate the gratings position.
Instead, the examiner
should show the grating frequently
in the same location.
The examiner is being shown
holding the cards
in a horizontal orientation,
which is the standard
and most common way
of presenting Teller Acuity Cards.
However, the cards may be held
in a vertical orientation,
with the grating either on the upper
or lower part of the card.
This can be a useful method
for testing patients
with nystagmus or strabismus.
During testing,
patients may wish to touch the grating
or may invertently touch it
when trying to point to the grating.
This should be avoided
by giving the child a soft toy to hold
and point toward the grating.
To keep the patient's attention,
the examiner can interact with
and reinforce the patient
for finding the grating location.
[no audible dialog]
Presenting a grating that has been
seen previously by the patient
can reestablish interest
in the testing
and also reassure the examiner
that the infant
is still attending
to the gratings.
[no audible dialog]
What behaviors
does the examiner use
to judge whether the patient
sees a grating?
The examiner must be aware of any
and all patient cues and behaviors
that indicate the location
of the grating.
Typically, in young infants,
a strong fixation response
to one side of the card,
presumably at the grating,
and then to the other side
when the card is rotated 180 degrees,
indicates the infant detects
that grating.
Finer gratings may not be
as strongly fixated,
yet will still elicit a consistent gaze
from the young infant.
Older infants and toddlers
may give brief glances to each side,
which are accepted as detection,
because the glance
is direct and clear,
and repeated
on subsequent presentations.
Some mature toddlers
and young children
may point to one side,
especially if prompted by the examiner,
such as,
"Where did the stripes go?"
This section illustrates
the complete sequence
of testing a child's visual acuity
with Teller Acuity Cards.
Young patients are usually seated
on their parent's lap,
and the parent or holder
should be cautioned
not to give the child any guidance
during testing.
Based on the patient's age,
determine the start card for testing.
Consult the Teller Acuity Card
Reference and Instruction Manual.
If the patient
is visually impaired,
a coarser grating than
that based on age
may be needed for the start card.
Distance of the card
from the patient's face
also depends upon age.
Consult the Teller Acuity Card
Reference and Instruction Manual.
The examiner
measures the test distance
from the patient's eyes
to the position the card is held.
For the 55-centimeter distance,
the length of the card
is an exact measure.
For the 38-centimeter distance,
used with young infants
and patients with limited vision,
a measuring tape can be used.
Or, a convenient measure
is the distance
between the examiner's elbow
and fingers,
with fingers either close or open,
depending
on the examiner's arm length.
This needs to be measured
before testing.
For 84-centimeter distance,
used with older children,
a measuring tape is needed.
Alternatively,
a measuring tape can be placed
on a table surface, adjacent
to the patient and the examiner,
with marks for each distance.
The examiner should check
the test distance periodically
during the testing,
as some patients will lean forward
to get closer to the gratings,
especially when they
become finer and more difficult to see.
Set up the cards in two stacks
with the grading face down
on a soft, clean surface.
The card labels are up.
One stack is for gratings
the patient has not seen,
or will not be tested on,
and the other stack is
for cards the patient has seen
or are larger
than need to be presented.
Stacking the cards
with the grating face down
keeps the examiner unaware
of the position
of the grading before testing.
It also minimizes damage
to the grating face of the card.
Papers can be inserted
between each card
in order to minimize marks
or blemishes.
The not-seen stack
has the start card top-most,
with progressively fine gratings
in series below the top card.
The seen stack
has the gratings that are coarser
than the start card,
in a series of progressively
wider stripes below the top card.
The examiner picks up the top card
from the not-seen stack,
and tests the infant
with this grating.
If she judges the infant
detects the grating,
she places it on the seen stack.
At some point, the series
of judgments will become difficult,
and the examiner may be unsure
whether the patient detects
that grating.
The examiner does not look
at the front of the card
for this grating location.
The examiner places the card
the infant does not detect
on top of the not-seen stack.
The examiner then retests
the previously seen grating.
And if she judges the infant
detects it,
she places the card on top
of the seen stack again.
[no audible dialog]
If the examiner still cannot determine
that the patient
detects the grating,
this indicates that a below-threshold
grating has been found,
and testing is completed.
The next-coarser grating,
the finest the patient
responds positively to,
is recorded
as the patient's acuity.
Sometimes, retesting results
in different decisions
on the patient's detection,
and the examiner must go back
and forth between several cards
to determine the patient's acuity.
After testing a patient,
the cards can be placed
in a single stack, ready for storage.
We recommend randomly
reordering the right-left locations
of the gratings to avoid
biasing the grating locations
to one side.
As indicated,
the finest or smallest grating size
that the patient is judged to see
by the examiner
defines their visual acuity.
The recording form shown
in the handbook
can be used to record information
about the patient,
such as name,
date of birth,
test date,
and age.
It is also used
to record the important results
of the acuity test,
including the acuity card
at threshold in cycles per centimeter,
test distance, and acuity conversion.
The examiner can take the value
from the "Teller Acuity Card Handbook,
Appendix D,"
showing conversions
from cycles per centimeter
to cycles per degree, Table 1,
and from cycles per centimeter
to Snellen equivalents.
The patient's acuity can be shown
on an age-norm graph
from the "Teller Acuity Card
Handbook."
The patient's age is noted
at the bottom of the graph.
The test distance is circled,
and the grating
in cycles per centimeter
in the column
under the test distance is also circled.
A line is drawn from this value
across to the patient's age.
This shows
where the patient's acuity
falls relative to the normal range
for that age.
All values are then recorded
in the results section
of the recording form.