Clinical performance of a handheld digital infrared monocular pupillometer for measurement of the dark-adapted pupil diameter

PURPOSE: To compare the accuracy of a handheld infrared digital pupillometer and digital infrared photography for measurement of the dark-adapted pupil diameter. SETTING: Department of Ophthalmology and Visual Sciences, Texas Tech University Health Sciences Center, Lubbock, Texas, USA. METHODS: The right horizontal pupil diameter in healthy volunteers was measured using a NeurOptics PLR-200 pupillometer and then videographed using the infrared function of a CyberShot video camera after 2 minutes and 5 minutes dark adaptation at 1 lux ambient illumination. The best still image was extracted from the video file, and the horizontal pupil diameter was determined by comparison against an internal photographic length standard using digital image software. Accommodation and alertness were controlled during testing. RESULTS: The mean horizontal pupil diameter by infrared photography after 2 minutes of dark adaptation by subject age was 7.71 mm for ages 20 to 29 years, 6.80 mm for ages 30 to 39 years, 6.53 mm for ages 40 to 49 years, 5.94 mm for ages 50 to 59 years, and 6.01 mm for ages 60 to 69 years. The mean difference (infrared photography minus pupillometer) was +0.09 mm (range +0.30 to -0.14 mm) at 2 minutes of adaptation and +0.07 mm (range +0.25 to -0.13 mm) at 5 minutes. CONCLUSIONS: The pupillometer accurately measured the horizontal pupil diameter at 1 lux, with no measurement more than 0.3 mm different from infrared photography measurements. The pupillometer had a slight negative bias that is unlikely to introduce an error greater than 0.5 mm in clinical measurements.