A new study has challenged the validity of using eyelid tremor as a sign of cannabis impairment by police officers. The study, conducted by researchers from Canada and the US, found that there was no significant association between recent cannabis use and the presence of eyelid tremor, as assessed by trained observers. The study also suggested that cannabis users were less likely to have eyelid tremors than non-users.
What is eyelid tremor and how is it used by police?
Eyelid tremor is a term that refers to involuntary and intermittent spasms of the eyelid muscles. It has often been associated with cannabis impairment and is one of the processes used by Drug Recognition Experts (DRE) to supposedly confirm if a driver is impaired by cannabis use, including the RCMP. DREs are police officers who have received special training in detecting drug impairment through a multi-step process that includes an examination of a person’s eyes.
According to the Drug Evaluation and Classification Program of the International Association of Chiefs of Police, eyelid tremor is one of the eye cues that indicate cannabis impairment, along with horizontal gaze nystagmus, lack of convergence, and pupil size. However, the accuracy and reliability of these eye cues have been questioned by several studies and experts.
How was the study conducted and what were the results?
The study, published in the journal Forensic Science International, involved about 100 participants who were divided into three categories: daily, occasional, and no current cannabis use. Participants then had their closed eyelids video recorded for 30 seconds by infrared videography goggles before and after smoking or vaping cannabis. Three observers with experience in eye movements and medical toxicology then reviewed these videos to determine which individuals had consumed or were impaired by cannabis based on a grading system.
The results showed that there was no significant association between recent cannabis use and the observers’ assessment that eyelid tremor was present. In fact, cannabis users were less likely to have eyelid tremors than non-users. The study also found that the inter-observer agreement was low, meaning that the observers did not consistently agree on whether eyelid tremor was present or not.
The study concluded that the weak association between recent cannabis use and eyelid tremor does not support this method in identifying recent cannabis use. The study also recommended that additional research is needed to identify the presence of eyelid tremor more accurately and to determine the relationship, if any, between cannabis dose and timeline in relation to last cannabis use to eyelid tremor and how, or if, it should be used for cannabis DRE examinations.
What are the implications and limitations of the study?
The study has important implications for the field of drug-impaired driving, as it suggests that eyelid tremor is not a reliable indicator of cannabis impairment and may lead to false positives or false negatives. This could have legal and social consequences for drivers who are accused or acquitted of cannabis impairment based on this method. The study also highlights the need for more objective and standardized methods of detecting cannabis impairment, such as oral fluid or breath testing devices.
However, the study also has some limitations that should be considered. For instance, the study only involved cannabis users who smoked or vaped cannabis, and did not include other modes of consumption, such as edibles or oils. The study also did not measure the actual THC levels in the participants’ blood or saliva, which could have provided more information about the relationship between cannabis use and eyelid tremor. Moreover, the study did not test the participants’ actual driving performance or cognitive abilities, which are more relevant indicators of impairment than eye movements.
