Measuring Pupillary Distance
Someone with training in the field of optics can accurately measure your pupillary distance. This is normally done with a small millimeter ruler referred to as a "PD stick" or with a corneal reflex pupillometer, which is a machine calibrated to help the optical professional more accurately measure the pupillary distance.
In very young children and babies, where the patient is unlikely to stay still, the optical professional will typically measure from one medial canthus to the other lateral canthus.
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