![]() Examiner II recorded it at 6.13 mm using the Rosenbaum, 6.58 mm with the millimeter rule, and 6.51 mm with the digital camera. In dim conditions, examiner I had a mean pupil-size estimation of 6.1 mm using the Rosenbaum, 6.6 mm with the millimeter rule, and 6.53 mm with the digital camera. The mean pupil sizes in bright light were 5.68 mm for examiner I and 5.3 mm for examiner II using the Rosenbaum method, 6.0 mm for examiner I and 6.13 mm for examiner II using the millimeter rule, and 6.0 mm for examiner I and 5.9 mm for examiner II using the digital camera (Table 1). This procedure was repeated for both eyes. The ruler was placed immediately underneath the lower eyelids. The horizontal diameter of the pupils was also measured using a regular millimeter ruler. Half of a millimeter is added to the reading if the pupil diameter is in between two gauges. This procedure was repeated for both eyes on all subjects. The subject’s pupil was compared with the different diameters from the gauge. The chart was placed at the temporal side of each subject with the printed comparison gauge at the level of the cornea. The size of each subject’s pupils was estimated using the Rosenbaum chart. A line was made from edge to edge of the pupil and the measurement was taken by comparing the length of the line to the ruler placed under the lid. The photos were enlarged using Adobe Photoshop (Adobe Systems Inc., San Jose, CA, USA). A white ruler was placed just under the lower lid and included in the photo to serve as a gauge. To minimize accommodation, the subjects were asked to fixate at a target coming from a laser pointer at a distance of 4 m. The subjects were allowed 5 minutes to adapt to each lighting condition. Measurements in bright setting were done first, followed by dim, then dark. One thousand lux was used for bright, 10 lux for dim, and < 1 lux for dark. A light meter measured the change in the lighting condition inside the room (4 m x 4 m). The camera’s shutter speed was fast enough to capture the image before the pupil could react to the flash. The digital camera was set to automatic flash. ![]() The camera was set up to take photos of the right eye of all the subjects first, and then repositioned for the left eye. The subject was positioned with the chin resting on the slit-lamp table (the slit-lamp was removed for this purpose). The digital camera with 22 mm lens and 6.1x magnification was mounted on a tripod and placed 53 centimeters in front of the subject’s eye. ![]() The digital photo measurements using a Sony DSC-P10 digital camera (Sony Electronics, Oradell, NJ, USA) were compared with the measurement taken with the use of Rosenbaum pupilcomparison gauge and direct millimeter rule. Each of the subjects underwent slit-lamp examination of the external and posterior part of the eye after which two examiners measured their pupil size. Excluded were those with history of eye trauma, intraocular surgery, and use of medicines (amphetamines, opiates) that could alter pupil function. The three methods were treated equally.įifteen volunteer medical students 23 to 36 years old (mean 27) with a pair of healthy eyes with normal pupil functions were enrolled in the study. A study by Twa has shown that estimation of pupil size by digital photography, though not fast in getting a result, was repeatable and more accurate than estimates using other clinical methods.5 Unlike the Twa study, where a standard measurement (infrared video recorder) was assigned as reference and 4 other methods of measurements were used (ruler, semicircular templates, Colvard pupilometry, digital camera), this study had no standard reference and used only 3 methods. Currently, the Colvard infrared pupilometer is considered the gold standard for pupil measurement.1 This paper introduces a method of pupil-size measurement using a digital camera. The instrument is accurate up to + 0.10 mm.4 Although accuracy and reliability are factors in choosing a device, one limiting factor that a clinician or center considers is cost. It can measure the pupil in 3 adjustable light settings (bright, dim, very dark). ![]() One of these devices is an infrared video camera that can calculate the average pupil size of 10 pupil images captured in 2 seconds. It has been shown that patients with large pupils express dissatisfaction with their surgery.1, 2 While most parameters measured before LASIK allow repeatable measurements with consistent results, pupil size has been the most difficult and inconsistent.3 Many devices have been developed for measuring pupil size, but these can be very expensive. PUPIL size is important in performing laser-assisted in situ keratomileusis (LASIK).
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