A variety of things can affect the results of the SFSTs. The officer is supposed to ask the suspect if they have any medical conditions that could affect their performance on any of the tests prior to administering them. Drugs, health issues, physical injuries, age, weight, and footwear can affect how someone does on an SFST.
Some drugs and health issues can affect HGN. Dissociative anesthetics, such as PCP, can cause resting nystagmus, which is the jerking of the eyes as they look straight ahead. Nystagmus can also be caused by certain pathological disorders, including brain tumors, brain damage, and some diseases of the inner ear.
For the One Leg Stand and the Walk and Turn, the officer is specifically supposed to ask the suspect if he or she has any leg or knee injuries that could affect their ability to stand, walk, or balance. Some studies suggested that individuals over 65 years old or people with back, leg, or inner ear problems have difficulty performing the Walk and Turn and One Leg Stand.
The 1984 SFST student manual stated that individuals who are 50 pounds or more overweight would have difficulty performing the Walk and Turn and One Leg Stand. The other thing that can impact an individual’s ability to perform the one-leg stand and walk-and-turn is wearing heels more than 2” high or other unusual footwear, such as flip flops. The officer is supposed to ask anyone wearing that type of footwear if they would like to remove their footwear.
Are There Any Factors That Could Exempt A Driver From Having To Take The Field Sobriety Tests?
There are some things that can exempt a driver from having to perform field sobriety tests. For example, if somebody is in a wheelchair, then there would be no way for them to perform the Walk and Turn and One Leg Stand. With regards to Horizontal Gaze Nystagmus, some things can change the ability to fully test the individual. These things include being blind in one eye or having a glass eye. If that’s the case, then the maximum number of clues that could be observed would be three because the officer would only be able to see three clues in the functional eye.
If the suspect states that they have a leg, knee, or ankle problem prior to performing the One Leg Stand or Walk and Turn, then the officer will likely ask the suspect to perform the tests anyway. The officer will then say that they took those injuries into consideration when evaluating the person for intoxication.
Source: NHTSA’s 2015 DWI Detection and Standardized Field Sobriety Testing student manual
For more information on What Can Affect A Field Sobriety Test Result, call (405) 633-3420 to speak with an attorney.