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:
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.
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.
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.
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.
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.
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 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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Good control of at least one eye:
Ability to maintain a position in front of the Eyegaze monitor:
Absence of medication side effects that affect Eyegaze operation:
Mental abilities that improve the probability for successful Eyegaze use:
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:
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.
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.
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.
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.
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.
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.
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.
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.
Amyotrophic Lateral Sclerosis (ALS):
Muscular Dystrophy, Spinal Muscular Atrophy, Werdnig-Hoffman syndrome:
Spinal Cord Injuries:
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 (800-904-7823)