A pupilometer is a device used in Opticianry that measures the distance between a patient’s pupils. It is held by the Optician and placed lightly against the forehead of the patient. Normally, the patient holds the other end for positioning purposes.
Inside is a light to which the patient focuses. The optician then measures the distance between the patient’s pupils with adjustments atop the device. It is with this pupillary distance that eyewear can be crafted to fit their individual needs. It the PD measurement is wrong, it will effect how the patient sees through his or her eyewear in a negative way.
Unless the patient has a form of strabismus, the right and left eyes usually measure the same or within two millimeters when measuring each eye individually.