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<< Continued From Page 1 HOW THE TEST WORKS As explained earlier, nystagmus means a jerking of the eyes. There are a number of different kinds of nystagmus, all of them influenced by alcohol. The test you will use at roadside is a test of "horizontal gaze nystagmus" - the nystagmus that occurs when the eyes gaze to the side. Many people will show some jerking if the eyes move far enough to the side. In intoxication, however, three signs will be observed: 1. The jerking of the eyes occurs much sooner. That is, the more intoxicated a person becomes, the less he has to move his eyes to the side in order for the jerking to occur. 2. If you have a suspect move his eyes as far to the side as possible, you can estimate in a general way the extent of intoxication. The greater the alcohol impairment, the more distinct the nystagmus will be in the extreme gaze position. 3. If the suspect is intoxicated, he cannot follow a slowly moving object smoothly with his eyes. ESTIMATING A 45-DEGREE ANGLE Since the extent of impairment is indicated by the angle at which nystagmus begins, you will need to learn how to estimate this angle... particularly the angle of 45-degrees, since that is the crucial point for estimating BAC. The page after the score sheets contains a square template you can use for practice. Cut this template out and attach it to a square of cardboard the same size for support. To use this device, hold it up so that the person's nose is above the diagonal line. Be certain that one edge of the template is centered on the nose and perpendicular to (or, at right angles to) the face. Have the person you are examining follow a penlight or some other item until he is looking down the 45-degree diagonal. Note the position of his eye. With practice, you should be able to recognize this angle without using the template. |
Copyright 2000 - 2008 |
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Examine the eyes of four or five people, so that you become familiar with what a 45-degree angle of gaze looks like. Next, practice without the device, but check your estimates periodically. Practice until you can consistently estimate 45 degrees. Check yourself monthly with the device to be sure that your accuracy has been sustained. SPECIFIC PROCEDURES Give the suspect the following instructions from a position of interrogation (that is, with your weapon away from the suspect): I AM GOING TO CHECK YOUR EYES. 'Request that the suspect remove glasses or hard contact lens at this time if they are being worn. Nystagmus is not influenced 1y how clearly the suspect can see the object he is to follow.) NOW KEEP YOUR HEAD STILL AM FOLLOW THIS (indicate what he is to follow) WITH YOUR EYES. DO NOT MOVE YOUR EYES BACK TO THE CENTER UNTIL I TELL YOU (If the suspect moves his head, use a flashlight or your free hand as a chinrest.) Check the suspect's right eye by moving the object to the suspect's right. Have the suspect follow the object until the eyes cannot move further to the side. Make this movement in about two seconds, and observe: 1) whether the suspect was able to follow the object smoothly or whether the motion was quite jerky; and 2) how distinct the nystagmus is at the maximum deviation. Estimate where a 45-degree angle would be using the training procedure given [above]. Move the object a second time to the 45-degree angle of gaze, taking about four seconds. As the eye follows the object, watch for it to start jerking back and forth. If you think you see nystagmus, stop the movement to see if the jerking continues. If it does, this point is the angle of onset. If it does not, keep moving the object until the jerking does occur or until you reach the imaginary 45 degree line. Note whether or not the onset occurs before the 45 degree angle of gaze. (The onset point at a BAC of 0.10 percent is about 40 degrees.) If the suspect's eyes start jerking before they, reach 45 degrees, check to see that some white of the eye is still showing on the side closest to the ear, as in the photograph. If no white of the eye is showing, you either have taken the eye too far to the side (that is, more than 45 degrees) or the person has unusual eyes that will not deviate very far to the side. Use the criteria of onset before 45 degrees only if you can see some white at the outside of the eye. AN EYE DEVIATED TO 40 DEGREES - NOTE THE AMOUNT OF WHITE SHOWING ON THE OUTSIDE (CLOSEST TO THE EAR) OF THE EYE. Repeat this entire procedure for the left eye. When observing the left eye at 45 degrees of gaze, some white of the eye again should be visible at the outside (closest to the ear) of the eye. NOTE: Nystagmus may be due to causes other than alcohol in three or four percent of the population. These other causes include seizure medications, phencyclidine (PCP), barbiturates and other depressants. A large disparity between the performance of the right and left eve may indicate brain damage. |
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San Francisco DUI Laws and Lawyers is provided as an information center for those facing criminal charges in San Francisco, San Mateo County, Marin County, Napa County, Sonoma County, Alameda County and Contra Costa County. It is also intended to counter the growing influence of radical groups pressuring courts, prosecutors and legislators for more unfair DUI laws, increasingly harsh punishment, more erosion of our Constitutional protections, and ultimately a return to the days of prohibition. The website for the National Motorists Association presents views on such important DUI-DWI issues as the constitutionality of roadblocks, reliance upon questionable breath tests, officer-administered license suspensions, and inappropriate penalties in drunk driving cases. |
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