Blog | Optical Industry Insights, Guides & Tools for Opticians

Pupillary distance (PD) is the measurement in millimeters between the centers of your two pupils. To measure it yourself, stand 18 inches from a bathroom mirror, hold a millimeter ruler flat against your brow, align the zero mark over your right pupil center, then close your right eye and read the mark that falls overContinue reading “How to Measure Your Pupillary Distance (PD): Ruler, Mirror, and App Methods”

The numbers stamped on a frame, such as 52□18-140, are the boxing system: eye size, bridge and temple length in millimeters. This guide decodes every frame measurement (A, B, DBL, ED), shows how they set frame PD and decentration, and how to tell whether a lens will physically fit.

There is a published answer to how accurate a PD, lens power and optical center have to be. ANSI Z80.1 and ISO 21987 set the tolerances a finished pair of glasses must meet. This guide gives the exact numbers and what they mean for measurement at the dispensing desk.

Prentice’s rule, prism equals decentration in centimeters times lens power, quantifies the unwanted prism created when the optical center is not in front of the pupil. This guide covers the formula, base direction, worked examples, and the vertical imbalance that anisometropia produces in down-gaze.

Monocular PD measures nose-bridge to each pupil individually; binocular PD is the total pupil-to-pupil distance. Near PD is smaller than distance PD due to convergence. This reference explains all four measurements, when each is required, and how conversion estimates work for dispensing.

Pupillary distance grows through childhood and stabilizes in adulthood. Learn when PD actually changes, why near PD differs from distance PD, and when re-measurement is worth doing.

A dispensing pupillometer is an optical instrument that measures interpupillary distance (PD) by projecting a coaxial light source onto the cornea and aligning crosshairs with the resulting corneal reflex in each eye. A digital model adds an electronic scale readout, eliminating the manual sliding cursor and giving the dispenser a precise numeric value for bothContinue reading “Digital Pupillometer: How It Works, Accuracy vs Manual, and the Smartphone Alternative”

Can a pupillary distance app measure PD accurately? See how PD apps work, how they compare to a ruler and pupillometer, and how to measure your PD with a phone.

For most adults, a normal pupillary distance falls between 50 mm and 75 mm, with the majority of the population clustered between 55 mm and 70 mm. Published clinical research puts the adult mean at roughly 62-63 mm overall, with men averaging about 63.6 mm and women about 61.1 mm. Optogrid’s own dataset of 14,904Continue reading “Average Pupillary Distance: Normal PD Values by Age, Gender, and Ethnicity”

Bifocals have two discrete focal zones separated by a visible segment line. Progressives eliminate the line and add a continuous power gradient through distance, intermediate, and near zones. Neither is universally better: the right choice depends on the wearer’s visual tasks, adaptation tolerance, and ADD power.