![]() 5 One possible reason for low reliability may not reside in the instruments themselves but in the technician's difficulty using such instruments. Viktorins method and pupilometer measurements have been criticized for lack of examination of reliability, and in the few studies where reliability has been examined, results have revealed poor reliability. However, the accuracy (i.e., the validity) was questioned, especially in IPDs that were especially large or small. However, the pupilometers were found to give consistent readings (i.e., were reliable) within the limits of clinically acceptable parameters. Sources of error were poor eye relief in all pupilometers and friction in the scale adjustments. 5 Obstfeld and Chou 12 examined nine of the leading pupilometers and found an average of 2.3-mm error (SD = 0.26 mm). Various inaccuracies in these measurement processes have been discussed, including parallax error (a large difference between the IPD of observer and participant), incorrect spacing between the participant and the observer, and/or incorrect positioning of measurement tools. Corneal reflection, the method used in the present study, measures the distance between the pupils through the reflection of infrared light on the eyes. Pupilometers are handheld ophthalmological devices that measure distance between the pupils by aligning the device with the corneal reflexes of the participant. Viktorins method uses a hand measure of IPD by measuring the distance between certain features in the eye. ![]() ![]() Numerous methods have been used in the measurement of IPD Viktorins method, pupilometers, and corneal reflection are each commonly used in clinical settings. It is therefore important to be able to measure these metrics reliability and accurately and to determine normative data against which a person can be measured. 10, 11 Stereo perception is important in rapid three-dimensional processing involved in driving a vehicle and catching a ball. For instance, IPD determines the amount of stereo separation of two images that are combined in the brain to produce stereo perception. Interpupillary distance and PD influence many vision components that are important in activities of daily living (ADLs) as well as peak performance in athletes and fighter pilots. Smaller pupils allow an increase in depth of focus, which in turn reduces the effect of refractive errors and errors in accommodation such as accommodative lag on the quality (blur) of the retinal image. ![]() 8 Depth of focus is related to pupil size. 7 A limitation of very small pupils can be diffraction however, this problem is less significant than the aberrations in larger pupil sizes as demonstrated by Howland and Howland. A larger pupil will allow more peripheral rays into the eye, resulting in high-order monochromatic aberrations that pose a problem with image quality when the PD is large. 5, 6ĭiameter of the pupil (PD) is another component of the eye that is measured and is related to image quality. IPD is measured using the distance between the centers of the pupils. 4 Furthermore, normative IPD data is important in the optical industry when fitting patients for glasses. Distance between the pupils, called interpupillary distance (IPD), is an important clinical measure used to identify potential vision issues such as stereo acuity, 1 near point convergence, 2 accommodation, 3 and other vision-related issues. ![]()
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