# Patent

## Title
System for analyzing eye responses to automatically determine impairment of a subject

## Abstract

The impairment determination system automatically determines impairment of a subject based on pupil movement, as well as pupil responses to illumination and target tracking for either eye or both eyes simultaneously. The impairment determination system automatically processes a series of digital image frames, taken during the execution of a predetermined test protocol, to determine pupil location, size, and responsiveness to changes in illumination, which data are used by the impairment determination system to determine impairment of the subject. The present impairment determination system uses a method for quickly and accurately localizing the subject's pupils, as well as their boundaries, area, and center coordinates, which data is used as part of the impairment determination process.

## Background
FIELD OF THE INVENTION
This invention relates to a system for non-invasively determining impairment of a subject by monitoring the subject's ocularmotor and pupillary responses to predetermined stimuli to enable the system to determine a subject's alertness and attention.
BACKGROUND OF THE INVENTION
It is a problem to determine whether a subject is impaired, regardless of whether this is due to a medical condition, or the use of alcohol or drugs, or whether the subject is suffering from sleep deprivation, or any other condition which interferes with the subject's ability to perform their assigned tasks. This is particularly a problem in the workplace where an employee who is presently functioning at a level of alertness that is less than their norm can place themselves and others in danger of injury, especially when the impaired employee is operating machinery. In addition, an impaired employee functions at a reduced level of efficiency, and the incidence of errors in the impaired employee's work product dramatically increases.
There is presently no automated system for quickly and accurately determining the impairment of large numbers of employees, so employers resort to random and expensive drug testing to detect the presence of impaired employees in the workplace. For example, urine-based drug testing does not test for impairment, only prior use, is limited to a few illegal substances, and does not deal with alcohol, medical conditions, or fatigue. Therefore, while this approach fails to provide any degree of effective screening of the entire workforce on a daily basis, it is expected that it does have some deterrent effect which decreases the incidence of impaired employees.
It is known that the determination of a subject's impairment can be accomplished by the measurement of the subject's eye gaze tracking and the monitoring of the subject's eye behavior, which measurements are compared to a normal response or a normal response for the subject, to determine a subject's alertness and attention. For example, by tracking and measuring the pupil responses of the subject, it is possible to determine the subject's impairment, since abnormal pupil dilation and pupil response to a stimulus are involuntary responses. These responses, in association with eye movement in tracking a visual stimulus, can definitively determine the impairment in a subject.
With all of these metrics available as impairment determination tools, the accurate measurement and tracking of the subject's pupil centroid location and determination of the area of the pupil are critical to the precise determination of impairment. It is also important to detect eye blinking to ensure that pupil measurements are not computed at those time instances when a blink occurs, since the pupil is either partially visible or not visible at all when a blink occurs.
Presently, all of these measurements are performed manually, with the accuracy and reliability of these measurements being subjective and possibly tainted by the ambient conditions under which the test is administered. Ambient conditions include the inability to maintain the subject's gaze in a fixed direction, erratic lighting conditions, and the subjective nature of the test administrator's administration of the test.
There have been some previous computer-based attempts to automate this process and quickly determine the exact area of a subject's pupil. These proposed processes have relied on either finding the darkest area on the image of the eye, and then thresholding within a range of this value to extract the pupil, or by attempting to fit an ellipse of predetermined diameter to the features present in the input image. Both approaches fail at producing an exact measurement of the pupil's location and area when light specularities or long eyelashes occlude the pupil, and when other dark regions are detected in addition to or instead of the pupil due to the presence of heavy eye makeup or bushy eyebrows. These complex conditions cause the subject's pupil to have a non-circular shape, which would be deformed by the ellipse fitting eye-response tracking process normally used to detect pupils and irises in human eyes, and other approaches based on the detection of the darkest point in the image would fail in the presence of eye makeup or thick eyebrows. These methods also have no means to compensate for specularities that can occur due to the lighting conditions.
Therefore, presently there is no viable automated impairment detection system that can be used to screen large numbers of subjects to quickly and accurately determine impairment of a subject.
BRIEF SUMMARY OF THE INVENTION
The above-described problems are solved and a technical advance achieved by the present system for analyzing eye responses to automatically determine impairment of a subject (termed “impairment determination system” herein). These eye responses include both ocularmotor and pupillary responses to illumination and target tracking for either eye or both eyes simultaneously. The impairment determination system uses a series of digital image frames of a subject's eyes, taken during the execution of a predetermined test protocol, which digital image frames are automatically processed to determine pupil location, size, and responsiveness to changes in illumination, which data are used by the impairment determination system to calculate impairment of the subject. Involuntary eye movements and/or pupil reactions are an indicator of physiological impairment, which is directly related to safety and fitness-for-duty issues in the workplace, on the highways, etc.
The impairment determination system obtains a series of digital image frames from a user interface device, which digital image frames capture and track pupil location and size, in response to the execution of a predetermined test protocol on the subject. A typical user interface device, known as an Ocular Motor Module (OMM), is illustrated in U.S. Pat. No. 5,137,345 and can be used to generate these digital image frames. This user interface device has light emitting diodes (LEDs) in place to act as the stimulus for left/right, up/down, and bright/dim activity. Cameras (and associated infrared lights) capture the subject's eye movements, as driven by the test protocol, and the resulting image frames are digitized for analysis. The horizontal, vertical, and oblique eye movement, eyelid blink activity, as well as the size and reactivity of the pupil, are the primary data that can be retrieved from the sequence of digital images. Thus, monitoring the subject's ocularmotor and pupillary responses enables the impairment determination system to determine the pupil area and location which can be used to determine a subject's alertness and attention.
The impairment determination process can maintain one or more test protocols that define a series of test stimuli. The impairment determination process also maintains one or more test responses, indicative of a normal eye movement response or the subject's normal eye movement response to a corresponding series of test stimuli. By matching the measured response of the subject to a given test protocol with the normal eye movement response or the previously-stored responses recorded for that subject for the same test protocol, the impairment determination process can make an accurate determination of the subject's condition.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a block diagram of the present impairment determination system;
FIG. 2 illustrates, in flow diagram form, the operation of the pupil detection and eye-response tracking algorithm process;
FIG. 3a illustrates a typical image of a subject's eye;
FIG. 3b illustrates the image of FIG. 3a with specularities removed;
FIG. 3c illustrates a block summed version of the image of 3b; 
FIG. 3d illustrates the image of FIG. 3b with candidate seed points indicated;
FIG. 3e illustrates the image of FIG. 3d with growing pupil extraction;
FIG. 3f illustrates the final image of the eye with the final pupil boundary and centroid results; and
FIG. 4 illustrates, in flow diagram form, the operation of the impairment determination process.



DETAILED DESCRIPTION OF THE INVENTION
In determining whether a subject is impaired, regardless of whether due to the use of alcohol or drugs, or whether the subject is suffering from sleep deprivation or other condition which interferes with the subject's ability to perform their assigned tasks, the measurement of the subject's eye gaze tracking and the monitoring of the subject's eye behavior can be used to determine a subject's alertness and attention. Throughout this application, reference is made to the effects of impairment by drugs. It is understood the term “drugs” herein includes not only medicinal substances and addictive narcotics, but also is to be understood to include any other ingested substance which affects the brain, such as alcoholic beverages and the like.
System Characteristics
FIG. 1 illustrates a block diagram of the present impairment determination system 100, where a user interface 101 is used to administer the predetermined test protocol to the subject and generate image data. The user interface 101 can be a device, such as that shown in the above-mentioned U.S. Pat. No. 5,137,345, which includes illumination devices (not shown), imaging devices (not shown), and apparatus (not shown) to position the subject's face with respect to the illumination devices and imaging devices. To detect movement of the eye in response to visible stimulus, illumination devices comprising a plurality of low intensity, visible light sources can be disposed horizontally and vertically within the user interface 101. The sequential illumination of the visible light sources simulates eye movement while precluding pupil reaction thereto. Alternatively, the subject's eye movement can simply be tracked and then compared to normal eye movement and/or eye movement of the subject in a previously administered test to make an accurate determination of the subject's condition. A source of electrical power, such as batteries, is provided to power the illumination devices and imaging devices. The imaging devices can be connected to an image recording device 102 for capturing and optionally storing image data if a record of the images is desired. The interconnection between the user interface 101 and the image recording device 102 can be wired or wireless, using a cable or wireless communication protocol, respectively.
In addition, a data processing system 104 processes the received images using the pupil tracking system 105. The received images are processed by a frame capture apparatus included in the data processing system 104 to form a time-wise sequence of digital image frames indicative of the subject's eye responses. A pupil detection and eye-response tracking process 105 performs an analysis of the digital image frames generated by the imaging devices as they are received to quickly and accurately localize the pupil's boundaries, area, and center coordinates in close-up digital imagery of the subject's eye(s) as captured with the imaging devices.
An impairment determination process 106 uses the processed digital image frames to determine impairment of the subject. The impairment determination process 106, in the present example, maintains one or more test protocols that can consist of a series of stimuli which follow a predefined pattern. The impairment determination process 106 also maintains one or more test responses, indicative of normal eye movement and/or the subject's normal eye movement response to a corresponding test stimulus, as determined during a previously administered test on the subject. By matching the measured response of the subject to a given test protocol with the normal responses, the impairment determination process 106 can make an accurate determination of the subject's condition. Since it is impossible for a subject to maintain a uniform level of impairment, the comparison of present test results to priorly stored test results ensures that any significant departure from the norm for this subject is detected.
FIG. 4 illustrates, in flow diagram form, the operation of the impairment determination process, inclusive of the operation of the pupil detection and eye-response tracking process 105. The impairment determination system 100 is activated at step 401 by a subject entering their unique identification indicia via a keypad, scanner device, wireless interface, etc., to distinguish this subject from others. The authentication of the subject can include a subject-specific password and/or the scanning of an immutable physical characteristic of the subject, such as a fingerprint, iris scan, voiceprint, etc. The impairment determination system 100 at step 402 analyzes the data provided by the subject and authenticates the identity of the subject based on previously stored identification criteria that have been stored for this subject. If there is a failure to match the subject with the stored identification criteria, the impairment determination system 100 rejects the subject at step 403 and generates an alarm indication that the subject is not a valid user. A match results in the impairment determination system 100 proceeding at step 404 to execute the pupil detection and eye-response tracking process 105 as is described below. The collection of this data is a condition precedent to the operation of the impairment determination process 106, which is described below.
Pupil Detection and Eye-Response Tracking Process
FIG. 2 illustrates, in flow diagram form, the operation of the pupil tracking process 105 which processes each digital image frame in a sequence of digital image frames received from the video capture device, and outputs data indicative of the pupil area and location, such as the digital image frame with the pupil boundary highlighted and crosshairs delineating the pupil centroid location. This pupil tracking process 105 is simply an example of how the pupil area and location can be computed and is not intended to limit the scope of the impairment determination system 100.
The video capture device generates a time sequence of digital image frames, each of which is an image of at least one of the subject's eyes. The video capture device can create a single image of one eye, both eyes, or paired image frames of the eyes, and the pupil detection and eye-response tracking process 105 may track the pupil in one or both of the subject's eyes. The present description refers to the processing of an image of one of the subject's eyes as the common descriptive example that is used for simplicity's sake and is intended to include all possible combinations of eye imaging and frame generation in all of these possible scenarios.
The pupil detection and eye-response tracking process 105 operates in the following manner. A digital image frame, as shown in FIG. 3a, from the video capture device is input to the process at step 201. This received digital image frame is processed by providing contrast enhancement at step 202 to improve the quality of the received image and then performing, at step 203, a blink test to determine whether the subject is blinking in this digital image frame. If a blink is detected at step 203, then an indication of a blink is produced at step 204, processing of this digital image frame by the pupil detection and eye-response tracking process 105 concludes and, at step 205, processing returns to step 201 to proceed with the next successively received image in the received sequence of digital image frames.
If no blink is detected, then the digital image frame is first processed at step 206 where bright specularities, such as 301 and 302 shown in FIG. 3a, in the image are filled in, as shown in FIG. 3b, to reduce their effect on the subsequent processing. It is then determined at step 207 whether this is the first digital image frame in a sequence and whether a seed point has been previously determined. If a seed point has been previously determined, processing advances to step 209 where the previously determined seed point is used but, if not, the process computes a seed point at step 208 and processing advances to step 209. The candidate seed points are identified by finding the darkest point in a coarsely encoded image, as shown in FIG. 3c, that is computed by summing the intensities in each 20×20 block of pixels in the digital image frame. Next, a region-growing method is applied at step 209 at the best candidate seed point (x, y), which is indicated as 303 in FIG. 3d, to extract the subject's pupil from the image. If the first extracted region as computed in step 209 fails the pupil geometry tests (e.g., is the extracted region circular?) as determined at step 210, at step 211 the system determines whether the process has exceeded the allowable number of cycles of this test. If it has not, processing returns to step 208 where the best alternate candidate seed point (x′, y′) is selected and the region-growing method is applied at step 209. If this cycle fails the pupil geometry test as determined at step 210, the digital image frame is rejected at step 214 and processing returns at step 215 to step 201, where the next digital image frame in the sequence is obtained.
Generally, the first seed point lies within the pupil region, so the alternative seed point is rarely used. In addition, if a blink or eye-view change did not occur in the previous frame, the previously determined pupil centroid location is used at step 207 as the best candidate seed point in order to speed up the processing.
Finally, an ellipse is fitted over the extracted pupil region at step 216 to smooth the contours of the pupil boundary, and then the pupil XY-centroid location and pupil area measurements are computed. The pupil area then is highlighted on the image and the pupil centroid location is indicated in the image, as shown in FIG. 3f at step 217. Processing of this image then concludes at step 218 and the process returns to step 201 to determine if there is another digital image frame in the sequence of received digital image frames.
Pupil Contrast Enhancement
As noted above, the pupil detection and eye-response tracking process 105 at step 202 performs a contrast enhancement process to improve the quality of the received image. Contrast enhancement is needed in cases where poor lighting conditions exist, such as the image darkening and blur that often occurs when the subject focuses their attention towards the extreme corners of the eye. Enhancing the contrast between the pupil's edge and the iris of the eye helps to segment the pupil from the rest of the eye. A non-linear contrast adjust approach can be used to rescale the distribution of intensities to enhance edge boundaries.
Blink Detection
As noted above, the pupil detection and eye-response tracking process 105 at step 203 performs a blink test. Frames that are part of a blinking motion should not be processed, since the pupil is either partially visible or not visible at all in the image frames where the subject is blinking. These images would produce erroneous pupil location data which corrupts the test results and could result in a false determination of impairment. Therefore, two preliminary blinking tests are performed on each image frame before they are processed and considered to be valid eye frames. These initial blinking tests are as follows:

    
    
        1. Chi-Squared Statistical Test: Compute the distribution of intensities (i.e., the grayscale histogram) of the present frame and compare its results with the histogram obtained from the previous digital image frame. Drastic changes in the distributions between adjacent digital image frames are reflected by high Chi-Squared statistics, signaling the starting or ending of a blink, or the change in the camera view from one eye to the other. Let X be the histogram of frame t and Y be the histogram of frame t+1, then the Chi-Squared statistic may be computed as:
    
    






  
    d
    ⁢
    
      
    
    ⁢
    
      
        χ
        2
      
      ⁡
      
        (
        
          X
          ,
          Y
        
        )
      
    
  
  =
  
    
      1
      2
    
    ⁢
    
      
        ∑
        
          i
          =
          1
        
        N
      
      ⁢
      
        
          
            (
            
              
                X
                i
              
              -
              
                Y
                i
              
            
            )
          
          2
        
        
          (
          
            
              X
              i
            
            +
            
              Y
              i
            
          
          )
        
      
    
  




    
    
        2. Low Intensity Distribution Test: An image containing a very low maximum intensity is either a blank frame (all black), or a very dark image with poor lighting, which does not provide the necessary contrast information needed to properly extract the pupil. This condition may occur if the subject's face is not firmly pressed up to the visor at the start of the test protocol or if they suddenly pull away during testing. Therefore, digital image frames with extremely low maximum intensity values are discarded.
    
    


Once a digital image frame is considered to be part of a blink movement, flags are set to disable further processing, and the output is a digital image frame with a white horizontal bar extending across the width of the image, indicating that a blink has been detected.
Specularity Removal
As noted above, the pupil detection and eye-response tracking process 105 at step 206 removes specularities from the received digital image frame. If a digital image frame contains light specularities occluding parts of the pupil, this disrupts the pupil's viewable area and, thus, interferes with the accuracy of the pupil measurements. For the determination of impairment, it is critical that the measurements be consistent and precise; therefore, all of the light specularities or bright areas should be removed from the image prior to finding the pupil and computing the statistics. Bright spots are detected by thresholding, and then filling in the holes using bilinear interpolation of the surrounding pixels. An example is shown in FIG. 3a, which illustrates the original image with specularities in the pupil region, while FIG. 3b illustrates the image after the system removes the specularities.
Seed Point Determination
To speed up the algorithm, the pupil centroid that was computed in the previous digital image frame is used as a seeding point for the present digital image frame, since the eye does not move significantly in the interval between successive frames of the series of digital image frames. If the previous digital image frame is unavailable, the candidate seed point is selected by searching for the darkest point in an image formed by summing the intensities in each 20×20 pixel image block. FIG. 3c shows the image that is formed using this procedure, and FIG. 3d illustrates the best seed point. When the region extracted using the best candidate seed point is determined to be non-pupil like, all blocks in the summed image near the seed point are masked out by increasing their intensity values, and the next darkest seed point is determined. The above-described process of growing the region and testing the geometry is repeated, but if the process fails for the second time, the digital image frame is rejected.
Pupil Extraction Via Region Growing
Having selected a seed point, a region is grown around the seed point using a region-growing algorithm designed to search for and include pixels in the boundary that are of similar color and intensity. The growth is halted at the strong edge boundaries where the pupil and iris meet. The following cost function is used for this process:




  
    C
    ⁡
    
      (
      
        x
        ,
        y
      
      )
    
  
  =
  
    
      γe
      
        
          
            (
            
              
                I
                ⁡
                
                  (
                  
                    x
                    ,
                    y
                  
                  )
                
              
              -
              
                μ
                0
              
            
            )
          
          2
        
        
          2
          ⁢
          
            σ
            0
            2
          
        
      
    
    +
    
      
        (
        
          1
          -
          γ
        
        )
      
      ⁢
      
        1
        
          1
          +
          
            
              
              
                ∇
                
                  I
                  ⁡
                  
                    (
                    
                      x
                      ,
                      y
                    
                    )
                  
                
              
              
            
            p
          
        
      
    
  




where μo and σo are the mean and standard deviation near the seed point, and p and γ are parameters determined empirically. This approach extracts the exact shape of the pupil, which is critical for the accurate computation of the pupil area and centroid location measurements.

Region Geometry Test

As noted above, the pupil detection and eye-response tracking process 105 at step 209 performs a pupil geometry test. After extracting a region, the process must make sure that it corresponds to the pupil and not to some other dark region in the digital image frame, such as the eyelashes, the eyebrows, or the corners of the eye. Therefore, the extracted region is tested for its perimeter, roundness, and circularity. These geometric features provide a measurement of how large and elliptical the extracted boundary is. Regions with very small area and/or non-elliptical are classified as not being part of the pupil and are discarded from further analysis. The perimeter is computed as the length of the boundary, and the roundness and circularity measures are computed as:




  Roundness
  =
  
    
      
        
        Perimerter
        
      
      2
    
    Area
  




and





  Circulatory
  =
  
    
      μ
      R
    
    
      σ
      R
    
  




where μo and σo are the mean and standard deviation of the radial distance from the centroid location to the shape of the boundary.

Compute Pupil Measurements

As noted above, the pupil detection and eye-response tracking process 105 at step 216 determines the characteristics of the detected pupil. If the extracted region is considered to be the pupil, its contour is smoothed by fitting an ellipse to the region, and then the process computes the area and XY-centroid location of the final boundary. The pixels corresponding to the extracted pupil region are highlighted, and cross-hairs are drawn at the coordinates of the pupil's centroid location. The pupil area and XY-centroid location are stored for use in the determination of impairment.
Impairment Determination Process
Upon completion of the image data processing by pupil detection and eye-response tracking process 105, impairment determination system 100 at step 405 can optionally store a sequence of processed digital image frames, each of which contains highlighted pixels corresponding to the extracted pupil region, and cross-hairs drawn at the coordinates of the pupil's centroid location, in a memory. The data indicative of pupil area and XY-centroid location can also optionally be stored for use in the determination of impairment. The impairment determination process 106 uses this pupil area and location data to determine whether a subject is impaired, regardless of whether which could be caused by a medical condition, or the use of alcohol or drugs, or the subject is suffering from sleep deprivation or any other condition which interferes with the subject's ability to perform their assigned tasks.
The impairment determination process 106 maintains one or more test protocols that define a set of test stimuli which typically consists of a target which follows a predefined pattern. The impairment determination process 106 also maintains one or more test responses, indicative of a normal eye response or the subject's normal eye movement response to a corresponding set of test stimuli, as determined during a previously administered test on this subject. At step 406, the impairment determination process 106 retrieves the normal test results for this subject. By matching the presently measured response of the subject to a given test protocol at step 407 with the subject's normal responses, the impairment determination process 106 can make an accurate determination of the subject's impairment. The matching can be based on an algorithmic computation of the subject's pupil location in each digital image frame of the successive digital image frames and the size of their pupil, or it can be a point-matching protocol to determine whether the pupil movement tracks within a predetermined range of movement. In any case, the delay in the subject's eyes responding to the test stimulus and the accuracy of the pupil movement in following the test stimulus, combined with pupil size, provide a precise determination of impairment. Thus, at step 408, the impairment determination process 106 determines whether the match process executed at step 407 has satisfied the match criteria and, if a match is confirmed, at step 409 the impairment determination system 100 produces an indication of no impairment for this subject. However, if the match process executed at step 407 fails to satisfy the match criteria, the impairment determination system 100 produces an indication of impairment for this subject at step 410.
Summary
The impairment determination system automatically determines impairment of a subject based on pupil movement, as well as pupil responses to illumination and target tracking for either eye or both eyes simultaneously. The impairment determination system automatically processes a series of digital image frames, taken during the execution of a predetermined stimulus protocol, to determine pupil location, size, and responsiveness to changes in illumination, which data are used by the impairment determination system to determine impairment of the subject. The present impairment determination system uses a method for quickly and accurately localizing the subject's pupils, as well as their boundaries, area, and center coordinates.

## Claims

1. An impairment determination system for automatically determining impairment of a subject based on pupil responses during administration of a test protocol to said subject, as recorded in a time-wise sequence of digital images of at least one of the subject's eyes taken during administration of said test protocol to said subject, comprising:
digital image processing means for identifying a location of a pupil of at least one of said subject's eyes in a plurality of said digital images in said sequence of digital images;
pupil size means for computing a size of said pupil in said plurality of said digital images in said sequence of digital images; and
impairment determining means, responsive to said location of a pupil and said size of said pupil in said plurality of said digital images in said sequence of digital images, for automatically determining whether said subject is impaired, comprising:
stimulus means for recording a position of a stimulus target, used to direct movement of said subject's eyes, with respect to each digital image in said time-wise sequence of digital images,
comparison means for contrasting said tracked eye movement in said sequence of digital images with said position of a stimulus target, and
pattern means for identifying a departure of said tracked eye movement in said sequence of digital images with said position of a stimulus target against at least one predetermined pattern, representative of eye movement of said subject corresponding to a priorly administered stimulus protocol.

2. The impairment determination system of claim 1 wherein said impairment determining means comprises:
pupil movement determining means, responsive to data indicative of said location of said pupil in said plurality of digital images, for tracking eye movement in said plurality of digital images.

3. The impairment determination system of claim 2 wherein said impairment determining means further comprises:
pattern means for identifying a departure of said tracked eye movement in said sequence of digital images against normal eye movement.

4. The impairment determination system of claim 2 wherein said impairment determining means further comprises:
pattern means for identifying a departure of said tracked eye movement in said sequence of digital images from normal eye movement when compared to at least one predetermined pattern, representative of eye movement of said subject corresponding to a priorly administered test.

5. The impairment determination system of claim 1 wherein said impairment determining means further comprises:
illumination responsiveness means for measuring pupil reaction to abrupt changes in lighting conditions; and
responsiveness test means, responsive to said pupil reaction to abrupt changes in lighting conditions failing to follow a predetermined pattern, for determining that said subject is impaired.

6. A method for automatically determining impairment of a subject based on pupil responses during administration of a test protocol to said subject, as recorded in a time-wise sequence of digital images of at least one of said subject's eyes taken during administration of said test protocol to said subject, comprising:
identifying a location of a pupil of at least one of said subject's eyes in a plurality of said digital images in said sequence of digital images;
computing a size of said pupil in said plurality of said digital images in said sequence of digital images; and
automatically determining, in response to said tracked eye movement and said size of said pupil, whether said subject is impaired, comprising:
recording a position of a stimulus target, used to direct movement of said subject's eyes, with respect to each digital image in said time-wise sequence of digital images,
contrasting said tracked eye movement in said sequence of digital images with said position of a stimulus target, and
identifying a departure of said tracked eye movement in said sequence of digital images with said position of a stimulus target against at least one predetermined pattern, representative of eye movement of said subject corresponding to a priorly administered stimulus protocol.

7. The method for automatically determining impairment of claim 6 wherein said step of determining means comprises:
pupil movement determining means, responsive to data indicative of said location of said pupil in said plurality of digital images, for tracking eye movement in said plurality of digital images.

8. The method for automatically determining impairment of claim 7 wherein said step of determining further comprises:
identifying a departure of said tracked eye movement in said sequence of digital images against normal eye movement.

9. The method for automatically determining impairment of claim 7 wherein said step of determining further comprises:
identifying a departure of said tracked eye movement in said sequence of digital images from normal eye movement when compared to at least one predetermined pattern, representative of eye movement of said subject corresponding to a priorly administered test.

10. The method for automatically determining impairment of claim 6 wherein said step of determining further comprises:
measuring pupil reaction to abrupt and sustained changes in lighting conditions; and
determining, in response to said pupil reaction to abrupt and sustained changes in lighting conditions failing to follow a predetermined pattern, that said subject is impaired.