The EyeBrain Tracker (EBT) is an eyetracking medical device, which uses algorithms to accurately track eye movements for the diagnosis of Parkinson’s disease and multiple sclerosis. The brain uses many different areas to produce eye movements, so if an area of the brain does not function well, the eye movements it controls will produce an abnormal behavior.

Fig. 1 – The Eyebrain Tracker (EBT).

Since 1965, eye movements have been used to evaluate abnormalities and provide a link to the diagnosis of patients with neurological disorders. In particular, oculomotor abnormalities were used to evaluate the effect of the treatment in such patients. The study of eye movements has since become a valuable source of information for scientists and clinicians, as well as for neurobiologists, for whom the study of the control of eye movements provides a unique opportunity to understand the operation of the brain.

The EBT is comprised of several components, including a computer with two screens, a helmet, three software programs, and a recording device for highfrequency, accurate eye movement measurements. The EBT is also the only device of its kind to have obtained CE marking for medical use.

The eye exam is simple to carry out, non-invasive, and the results can be available in less than 20 minutes, even for patients at later stages of disease. Neurologists, ophthalmologists, and psychiatrists can learn to use the device with four hours of training.

During the exam, patients sit in front of a screen that displays ocular simulations to allow for automatic test analyses of their eye movements.

One of the tests, called “gap,” involves the display of a fixation cross in the center of the screen for 2,500–3,500 ms, and then removes the fixation cross for a time gap of 200 ms, followed by the appearance of a target on the right or on the left of the screen for 1,000 ms. This sequence is repeated for one minute and patients look at the fixation cross and the target as they appear. This test allows for the examination of reflexive saccades, which are rapid eye movements shifting the line of sight between successive points of fixation.

Different parameters of the saccades are automatically extracted and compared to normal values. One of these parameters is the reaction time (latency), which is the interval between the appearance of the target and the time when saccades start, while others include the saccadic velocity or the saccadic trajectory. Another type of test is called the “up down test” where the fixation cross is presented again for 2,500 to 3,500 ms. After the fixation cross is removed and a target is presented for 1,000 ms above or below the preceding position without a ‘time gap.’ As before, the sequence will be repeated for one minute. The patient looks at the fixation cross and the target when they appear. Measured parameters are the same as in the case of the gap test.

Fig. 2 – The eye exam uses ocular simulations to analyze the patient’s eye movements.

A third type, called the “antisaccades test,” allows for the investigation of the control of voluntary saccades. Patients are required to suppress a saccade (the ‘prosaccade’) toward a stimulus that appears in the periphery vision, and asked to generate a voluntary saccade of equal size to the opposite side (the “antisaccade”) instead. Again, the stimuli displayed are the same as during the gap test, while the analyzed parameters include the number of errors as well as latency.

A fourth test called “pursuit” shows a target that is moving either horizontally or vertically, which the patient then needs to follow. In this kind of test, analyzers are monitoring the presence of jerks in the eye movements.

As patients use the EBT, any delay in being able to react or fixate on the target could be an indication of a neurological condition. For example, if a patient has difficulty in being able to normally move their eyes from the fixation cross to a target in the up down test, it is typically associated with that part of the brainstem not functioning well, which could suggest progressive supranuclear palsy (PSP), a Parkinsonian disorder.

As various Parkinsonian disorders involve different brain areas, it is possible to differentiate between them by determining which parameters of eye movements are normal. In this way, the EBT device allows clinicians to rely on a simple set of eye movement parameters to differentiate between very similar syndromes, such as PSP, cortico-basal degeneration (CBD), or multiple system atrophy (MSA).

To identify multiple sclerosis, practitioners will be looking for patients who display a different velocity in the movements of each individual eye, while moving toward a target in a gap test, which is a symptom of damage of the brain’s white matter of the internuclear neurons.

Recently, a new software version of the EBT device has allowed it to help with the diagnosis of multiple sclerosis by confirming eye motricity impairment, which is a sensitive marker for this pathology. It can also be used to help monitor patients' progress and verify the effect of prescribed therapies.

People with multiple sclerosis often suffer from transitory or permanent neuro-ophthalmological problems, with disruptions in eye movements affecting 60 to 80 percent of these patients. The most commonly observed abnormalities are alterations in saccades and pursuits (tracking movements), as well as anomalies in patients’ ability to focus and hold a look.

These tests enable various parameters to be evaluated, including reaction time, eye movement velocity, eye trajectory, and the accuracy of the gaze, as well as cognitive functions such as preparation, activation, or inhibition of the movement. They also allow for a number of parameters to be compared with subjects who display normal eye movements.

The EBT technology is already being used in hospitals to help with the early characterization of Parkinsonian syndromes, to assist in the diagnosis of multiple sclerosis, and to monitor the development of these pathologies. It is also being tested to assess its potential for diagnosing and monitoring patients with dyslexia.

The technology was developed by EyeBrain, Paris, France. For more information about the company and the EyeBrain Tracker, please visit .