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Where the iris ends and the pupil begins

1 May 1999


Specially trained police officers known as Drug Recognition Experts (DRE) use pupil size to determine the type of substance a suspect drug user has taken. The DRE's use a defined program for evaluating pupil sizes. Part of the program consists of taking pupil measurements in standard room illumination as well as in dark room conditions. Three different methods of pupil measurement are taken in the dark room. These measurements are taken with a direct, diffuse, and shielded penlight. The dark room measurements can be difficult to obtain, especially in people with dark iridis. An ultraviolet light source may aid in the measurement of dark irides by causing the lens to fluoresce, thereby silhouetting the pupil. To determine if the UV light source would affect the pupil size differently than the penlight, the two methods were compared. These comparisons were made with the same DRE officer measuring the same subject during two separate sessions. There was no significant difference in pupil sizes between the UV light source and the DRE standard program of pupil measuring. The data collected was also used to determine if the DRE officers are reliable and consistent when evaluating pupils. The DRE officers were accurate to within 0.5mm between the two pupil measurements taken on the same individual at different times. The DRE program has pre-determined pupil size limits for passing and failing suspects. It was found that the upper limit of what the DRE protocol accepts as normal pupil size be raised from 6.5mm to 8.5mm.


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