Good pupillometry practice therefore dictates taking the PD monocularly, using the occlusion bar and noting any measurement differences indicated. Phorias: Some patients, especially without their habitual Rx in place during the PD measurement, will reveal a latent phoria which will impact the final measurement accuracy. In some cases, patients will also slowly rotate their head during the measurement process, which will also impact accuracy. In all cases, the operator should take a bird’s eye view of the patient’s forehead and eye placement, and note where any forehead asymmetry could impact the accuracy of the values found. Therefore, the operator must ensure the forehead bar is in equal contact with the patient’s forehead. Oftentimes, when the vertex distance between the eyes is not symmetrical, errors of parallax might affect the monocular values found. ![]() Find the most parallax-free point by experimenting with your eye position until the shifting of your gaze as you mark the right and left eye produces the least apparent shift of the alignment mark against the corneal reflection.įorehead rest: The forehead rest bar was designed to align the pupilometer’s reference scales to an equal vertex distance from the eye. If you notice the alignment marks shift with respect to the patient’s corneal reflex, you have parallax. The easiest way to check if your pupilometer is susceptible to operator parallax is to move your eye position closer to and further away from the eye viewing port while taking various PD measurements. Parallax: Not every pupilometer is designed to reduce error from operator-induced parallax. By doing so, you’ll reduce the uncertainty in your measurements: ![]() With an instrument assumed to be in good order, always keep the following areas of potential error in mind. This article will explain some basic pupillometry techniques along, with some ophthalmic optics principles as they relate to vision and eye movement.įor starters, we’ll assume your favorite pupilometer is in proper operational order and properly calibrated-meaning the PD values found are accurately indicated by the instrument’s scales. The tools for doing this range from simple PD rulers to digital pupilometers (also spelled “pupillometers”) to sophisticated digital centration systems that allow for various other measurements to be taken. One of the basic tasks in ophthalmic dispensing is measuring the distance between a patient’s pupils, a prerequisite for properly positioning and fitting eyeglasses.
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