Dark Adapted Threshold
Multifocal ERG (mfERG)
Preferential Looking (PL)
Visual Evoked Potential (VEP)
Dark Adapted Threshold (DAT) Top
The dark adapted threshold test (DAT)
evaluates night vision using dim spots of
light in a dark room. It helps us determine the minimum light level that an
infant or child can detect. With increasing time in the dark, the cells of
the retina become more sensitive to light. Therefore, before testing begins,
the child sits in the dark for 30 minutes to allow his/her eyes to become
Once the eyes have adapted to the darkness, the child views a
black screen onto which dim spots of light are projected. The spots are
projected one at a time, either to the right or to the left side of the
screen, and as the test proceeds, the spots become dimmer and dimmer.
Children are asked to point to the spots until they can no longer detect
them. The dimmest intensity that the child can detect is his/her dark adapted
infants are tested, an observer with a night vision camera attempts to
determine the location of the spots based on the infant's head and eye
movements. The infant's threshold is defined as the dimmest intensity for
which the observer can reliably identify the location of the stimulus.
entire test, including the period of dark adaptation, typically takes less
than an hour.
See Patient Information for additional DAT
(ERG) is an eye test that evaluates the function of the retina, the film that
lines the inside of the eye. The ERG test helps diagnose diseases of the
During the ERG test, the cells of the retina
(rods and cones) release tiny amounts of electricity in response to flashes
of light. If we know exactly how much light enters the eye and how much
electricity comes out, we can figure out how the rods and cones are
working. To pick up the electricity from the retina, a special contact lens
is placed on the surface of the eye.
prepare for the ERG test, drops are placed in the child's eyes to dilate the
pupils. These drops are the same drops that eye doctors routinely use for eye
examinations. The child then sits in a dark room for 30 minutes to allow the
pupils to dilate. Also, since the retina become more sensitive to light with
increasing time in the dark, the retina will give its strongest response
following this period of dark adaptation.
dark adaptation, anesthetic drops are given and a contact lens is placed on
the child's eye. (Often, both eyes are tested at the same time.) Once the
contact lens is in place, responses are recorded to a series of blue and red
lights. This part of the test may take 30 to 45 minutes. The total time for
the ERG test (including the period of dilation and dark adaptation) is
approximately 1.5 hours.
See Patient Information for additional details
on awake ERG testing and ERG testing under
Multifocal ERG (mfERG) Top
A new type of electroretinogram,
called the multifocal ERG (mfERG), allows responses to be simultaneously
recorded from multiple retinal areas using a stimulus array made up of black
and white, flickering hexagons (a). The results can be analyzed to provide a
contour map (b) of the function of the center of the retina, called the
macula. This is the specialized part of the eye that is used to read letters.
It is also the last part of the retina to develop.
To prepare for the ERG test, drops are placed in the child's
eyes to dilate the pupils. These drops are the same drops that eye doctors
routinely use for eye examinations. They take about 30 minutes to take full
effect. Next, anesthetic drops are given and a special contact lens is placed
on the eye.
is positioned on the doctor's lap in front of a video monitor. The contact
lens picks up electrical signals produced by the retina, following which a
map of the functional integrity of the retina is plotted.
for actual recording is typically 20-30 minutes; the total time (including
dilation) is typically less than an hour.
Looking (PL) Top
Looking test is used to assess visual acuity in infants and young children
who are unable to identify pictures or letters. The child is presented with
two stimulus fields, one with stripes and the other with a homogeneous gray
area of the same average luminance as the striped field. The location of the
stripes is randomly alternated. Typically, infants and children will look at
the more interesting stripes (if they can detect them) rather than at the
diagram, the baby is shown in an infant seat; alternatively, the child may
sit on an adult's lap or be held over the shoulder. A small peephole is
centered between the two fields. An observer views the child through the
peephole and judges the location of the stripes based on the child's head and
If the child can see the stripes, he/she will prefer to
look at them. If the child cannot see them, the striped field will look the
same as the blank gray field, and the child will not show a preference. The
smallest stripe width for which the observer can consistently identify the
location of the stripes is considered to be the child's resolution threshold
Evoked Potential (VEP) Top
In adults and
cooperative older children, visual acuity (the ability to see fine detail and
patterns) is measured using a letter chart. For those who are unable to read
the letter chart, the visual evoked potential (VEP) can be used. It measures
acuity by assessing the response of the brain to alternating black and white
stripes or checks. This acuity test is most helpful for testing youngsters
for whom other vision tests, like the preferential looking test, give
ambiguous or incomplete information about visual acuity.
To do the test, three small metal discs are
placed on the child's head. They are held in place by paste (similar to
toothpaste) and a band wrapped around the head. The discs are connected by
wires to a computer.
is then positioned in front of a TV screen displaying alternating black and
white stripes that progressively get narrower. As the child views the
stripes, a signal is relayed from the eyes to the brain (the visual cortex).
This signal is detected by the electrodes. The test is designed to find the
finest black and white stripes that reliably produce a response.
vision of each eye is tested separately; a patch is used to cover the
non-tested eye. The test typically takes less than an hour, depending on the
child's ability to cooperate.
See Patient Information for additional details
on VEP testing.