Promotional Hand Tools, Pupil Gauge Penlight - LED & Medical Grade, This pen light includes a pupil gauge with measurements from 2 to 9mm, to assist doctors in measuring the size of the patient's pupil dilation. Press the pocket clip to activate a white LED light to be used as a light source when examining injuries. Batteries are included (3x LR41), inserted, but not replaceable. ... #PGP120 $2.35/each.