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.