DETAILED
MEDICAL AND TECHNICAL INFORMATION
Eyegaze
Communication System
How does Eyegaze work?
The Eyegaze System is a direct-select vision-controlled
communication and control system. An Eyegaze user can perform
a broad variety of functions including speech synthesis,
environmental control (lights and appliances), typing, operating
a television, and running both mouse- and keyboard-controlled
applications on a second PC. Selections are made by looking
at boxes or "keys" displayed on the Eyegaze System's screen.
Nothing is attached to the user. Eyegaze programs vary from
simple teaching programs, where the screen is divided into
two or four large boxes (keys), to entire on-screen computer
keyboards with 75 or more 5/8-inch square keys. Eyegaze
users range in age from 5 years to 80 years old.
The Eyegaze System uses the pupil-center/corneal-reflection
method to determine where the user is looking on the screen.
An infrared-sensitive video camera, mounted beneath the
System's monitor, takes 60 pictures per second of the user's
eye. A low power, infrared light emitting diode (LED), mounted
in the center of the camera's lens illuminates the eye.
The LED reflects a small bit of light off the surface of
the eye's cornea. The light also shines through the pupil
and reflects off of the retina, the back surface of the
eye, and causes the pupil to appear white. The bright-pupil
effect enhances the camera's image of the pupil and makes
it easier for the image processing functions to locate the
center of the pupil. The computer calculates the person's
gazepoint, i.e., the coordinates of where he is looking
on the screen, based on the relative positions of the pupil
center and corneal reflection within the video image of
the eye. Typically the Eyegaze System predicts the gazepoint
with an average accuracy of a quarter inch or better.
Prior to operating the eyetracking applications,
the Eyegaze System must learn several physiological properties
of a user's eye in order to be able to project his gazepoint
accurately. The system learns these properties by performing
a calibration procedure. The user calibrates the system
by fixing his gaze on a small circle displayed on the screen,
and following it as it moves around the screen. The calibration
procedure usually takes about 15 seconds, and the user does
not need to recalibrate if he moves away from the Eyegaze
System and returns later.
The following physical abilities contribute
to successful Eyegaze use:
- Good control of at least one eye:
The user must be able to look up, down,
left and right. He must be able to fix his gaze on all
areas of a 15-inch screen that is about 24 inches in front
of his face. He must be able to focus on one spot for
at least 1/2 second. Several common eye movement problems
may interfere with Eyegaze use. These include:
Nystagmus
(constant, involuntary movement of the eyeball):
The user may not be able to fix his
gaze long enough to make eyegaze selections.
Alternating strabismus
(eyes cannot be directed to the same object, either
one deviates):
The Eyegaze System is constantly tracking
the same single eye. If, for example, a user with alternating
strabismus is operating the Eyegaze System with the
right eye, and that eye begins to deviate, the left
eye will take over and focus on the screen. The Eyegaze
camera, however, will continue to take pictures of the
right eye, and the System will not be able to determine
where the user's left eye is focused. When the left
eye deviates and the right eye is again fixed on the
screen the Eyegaze System will resume predicting the
gazepoint. Putting a partial eye patch over the nasal
side of the eye not being observed by the camera often
solves this tracking problem. Since only the unpatched
eye can see the screen, it will continuously focus on
the screen. By applying only a nasal-side patch to the
other eye, the user will retain peripheral vision on
that side.
- Adequate vision:
Several common vision problems may affect
a user's ability to see text clearly on the Eyegaze monitor.
These include the following:
Inadequate Visual acuity:
The user must be able to see text on
the screen clearly. If, prior to his injury or the onset
of his illness he wore glasses, he may need corrective
lenses to operate the Eyegaze System. If he's over 40
years old and has not had his vision checked recently,
he might need reading glasses in order to see the screen
clearly.
In most cases, eyetracking works well
with glasses. The calibration procedure accommodates
for the refractive properties of most lenses. Hard-line
bifocals can be a problem if the lens boundary splits
the image of the pupil, making it difficult for the
System's image processing software to determine the
pupil center accurately. Graded bifocals, however, typically
do not interfere with eyetracking.
Soft contact lenses that cover all or
most of the cornea generally work well with the Eyegaze
System. The corneal reflection is obtained from the
contact lens surface rather than the cornea itself.
Small, hard contacts can interfere, if the lens moves
around considerably on the cornea and causes the corneal
reflection to move across the discontinuity between
the contact lens and the cornea.
Diplopia
(double vision):
Diplopia may be the result of an injury
to the brain, or a side effect of many commonly prescribed
medications, and may make it difficult for the user
to fix his gaze on a given point. Partially patching
the eye not being tracked may alleviate double vision
during Eyegaze System operation.
Blurred vision:
This is another occurrence associated
with some brain injuries, as well as a side effect of
medications. A blurred image on the screen decreases
the accuracy of eye fixations.
Cataracts
(clouding of the lens of the eye):
If a cataract has formed on the portion
of the lens that covers the pupil, it may prevent light
from passing through the pupil to reflect off the retina.
Without a good retinal reflection the Eyegaze System
cannot accurately predict the user's eye fixations.
The clouded lens may also make it difficult for a user
to see text on the screen clearly. Surgical removal
of the cataracts will normally solve the problem and
make Eyegaze use possible.
Homonymous hemianopsia
(blindness or defective vision in the right or left
halves of the visual fields of both eyes):
This may make calibration almost impossible
if the user cannot see calibration points on one side
of the screen.
- Ability to maintain a position in front of the Eyegaze
monitor:
It is generally easiest to run the System
from an upright, seated position, with the head centered
in front of the Eyegaze monitor. However the Eyegaze System
can be operated from a semi-reclined position if necessary.
Continuous, uncontrolled head movement
can make Eyegaze operation difficult, since the Eyegaze
System must relocate the eye each time the user moves
away from the camera's field of view and then returns.
Even though the System's eye search is completed in just
a second or two, it will be more tiring for a user with
constant head movement to operate the System.
- Absence of medication side effects that affect Eyegaze
operation:
Many commonly prescribed medications have
potential side effects that can make it difficult to operate
Eyegaze. Anticonvulsants (seizure drugs) can cause: nystagmus,
blurred vision, diplopia, dizziness, drowsiness, headache
and confusion. Some antidepressants can cause blurred
vision and mydriasis ( abnormally dilated pupil.) And
Baclofen, a drug commonly used to decrease muscle spasms,
can cause dizziness, drowsiness, headache, disorientation,
blurred vision and mydriasis. Mydriasis can be severe
enough to block eyetracking. If the retinal reflection
is extremely bright, and the corneal reflection is sitting
on top of a big, bright pupil, the corneal reflection
may be indistinguishable and therefore unreadable by the
computer.
- Mental abilities that improve the probability for
successful Eyegaze use:
Cognition:
Cognitive level may be difficult to assess
in someone who is locked in, especially if a rudimentary
communication system has not been established. In general,
a user with average or better intelligence will best maximize
the capabilities of an Eyegaze System.
Ability to read:
At present, the Eyegaze System is configured
for users who are literate. The System is text-based.
A young child with average intelligence may not be reading
yet, but probably has the capability to learn to read
at an average age. He may be able to recognize words,
and may be moving his eyes in a left to right pattern
in preparation for reading. As an interim solution many
teachers and parents stick pictures directly onto the
screen. When the child looks at the picture he activates
the Eyegaze key that is located directly underneath it.
Memory:
Memory deficits are a particular concern
in considering the Eyegaze System for someone with a brain
injury. A user who can't remember from one day to the
next how to operate the system may find it too difficult
to use effectively.
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The client's medical diagnosis may also
provide considerable help in pre-determining the likelihood
of successful Eyegaze operation. Using medical diagnosis
as a starting point, the following conditions may exist,
and may affect optimum Eyegaze operation:
- Amyotrophic Lateral Sclerosis (ALS):
People with ALS are generally successful
operating the Eyegaze System. Cognition and intelligence
are usually unaffected, and so usually is eye control.
We have, however, seen limited eye movement in some people
with ALS, which made it difficult or impossible for them
to perform the more complex Eyegaze functions, such as
typing, on traditional direct-select Eyegaze keyboards.
Several new Eyegaze keyboards designed for users with
limited eye movement are now making it possible for most
users with ALS to continue to operate the Eyegaze System
indefinitely.
A common problem for users with ALS is
dryness of the eyes. The corneas are normally moistened
by tears, which are spread around by blinking. As the
blink reflex decreases, the corneas dry out, and don't
reflect infrared light very well. The Eyegaze System needs
to see a corneal reflection in order to function. Over-the-counter
artificial tears eye drops will often solve the problem.
- Brain injuries:
Traumatic and anoxic brain injuries can
result in a variety of problems that may have an effect
on Eyegaze operation. Cognition, memory, concentration,
or even the ability to read may be affected by the injury.
Vision problems are also common. In general, if the person
has a consistent way to communicate yes and no,
we assume there is a level of cognition that is sufficient
for some Eyegaze use. Often memory and attention problems
become apparent during the process of evaluating the user
with Eyegaze. Vision problems such as diplopia, blurred
vision, alternating strabismus and homonymous hemianopsia
may also impede Eyegaze use.
- Cerebral palsy:
People with severe cerebral palsy who
are able to maintain a stable head position, either on
their own or supported by a head rest, and who do not
have significant eye control problems, often do quite
well with the Eyegaze System. A number of children with
cerebral palsy are currently using Eyegaze Systems to
participate in school, from kindergarten through college.
People with CP who have uncontrollable head motion do
not find Eyegaze System operation acceptable, since the
fixed camera can only accommodate for head movement across
a two-inch range. Attempting to physically hold the head
of someone with spastic cerebral palsy does not usually
help. A variety of eye control problems are also often
associated with CP, most commonly alternating strabismus.
Applying a nasal-side patch to the eye that is not being
tracked may solve the problem. Finally, cognitive deficits
may be a limiting factor.
- Multiple sclerosis:
This disease does not, in our experience,
cause any physical limitations that prevent the Eyegaze
System from tracking the eye. However, if the multiple
sclerosis has affected vision, the user may not be able
to see well enough to read the screens, even though the
computer can track his eye just fine. A simple way to
determine the presence of this type of vision problem
is to position the potential user about 24 inches away
from any standard color computer monitor and ask him if
he can read typed text on the screen. Additionally, people
with MS who have taken steroids may have cataracts, a
common side effect of frequent steroid use.
- Muscular Dystrophy, Spinal Muscular Atrophy, Werdnig-Hoffman
syndrome:
We have not to date discovered any limitations
to Eyegaze use caused by these diseases. However, we have
seen several children with Werdnig-Hoffman syndrome who
have anoxic brain injuries that limit Eyegaze System use.
- Rett syndrome:
After evaluating several dozen girls with
Rett syndrome we have not determined any predictors for
successful Eyegaze use. Many of the girls were too easily
distracted to use Eyegaze in any meaningful way, although
they were able to calibrate without difficulty. There
is currently one Eyegaze user with Rett syndrome.
- Spinal Cord Injuries:
Quadriplegia resulting from spinal cord
injury presents no limitations for Eyegaze operation.
The system is often an excellent tool for people who are
ventilator-dependent quadriplegic, especially if they
are non-verbal. It is also being used by some people with
spinal cord injuries who are verbal, or who are able to
move their heads, but find direct-selection with the eyes
a faster and easier method of computer access than alternative
methods of row/column scanning, voice control, or mouth
or unicorn sticks.
- Strokes:
Brain attacks in the pontine (brainstem)
region often result in "locked-in syndrome", leaving the
person cognitively intact but with no means of communication
other than with the eyes. Concurrent cranial nerve damage
can affect the eyes as well, often limiting horizontal
eye movement. Many people with brainstem strokes are able
to operate the Eyegaze System in spite of some limitations
in eye movement, although it may be somewhat more difficult
for them to do than it is for someone with full eye control.
Ambient infrared light:
The Eyegaze System must be operated in an environment
where there is limited ambient infrared light. Common
sources of infrared light are sunlight and incandescent
light bulbs. The System makes its predictions based on
the assumption that the only source of infrared light
shining on the user's eye is coming from the center of
the camera. Therefore, stray sources of infrared may degrade
the accuracy or prevent Eyegaze operation altogether.
The System works best away from windows, and in a room
lit with fluorescent or mercury-vapor lights, which are
low in infrared.
If you have questions
about the suitability of the Eyegaze System for a particular
client,
please call us (800-393-4293) and ask to speak to one of
our nurses.
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