I wonder if you could help me with a query. It's about how pupillary distances are expressed. I've seen mine written as '32.5 mono'. I've seen another person's I've as '60'.

I assume that one is referring to the distance from one pupil to the center, and the other the distance between pupils? Do you know which is the normal way of expressing pupillary distance, and what mono means in this context? - Aviator

Cara

Pupillary distances can in fact be written two ways.

A standard pupillary distance is from the edge of one pupil to the other. There is a distance pupillary distance and a near pupillary distance, because when you look down to read, your eyes turn in somewhat. A typical standard pupillary distance could be 62/59. Generally there's about a 3 mm difference between near and far.

A monocular pupillary distance is especially helpful when a patient is either ordering a progressive addition lens or if they're high power. This is because most people are asymmetrical from the eye to the center of the nose, and centering is critical in both of the above cases.

Glasseslover

Pupillary distance can either be measured binocular or monocular.

When it is binocular it is the distance between the center of the pupils expressed in millimeters. When it is monocular, it is the distance from the center of the pupil in each eye to the center of the bridge of the glasses, also expressed in millimeters.

Hence, a binocular pupillary distance of 62 would not necessarily result in monocular pupillary distances of 31 mm each as there are of course variances with the individual pupils and the frames themselves. It is quite common in those circumstances to find a mono pupillary distance of: OD 30.5, OS 31.5, etc. as long as they add up to the total bino pupillary distance of 62.

Whether you use bino or mono depends on lens type and lens material. In polycarb and HI plastic single vision lenses we always use mono. In all other materials, both single vision and straight top bifocals we use bino (and decenter the reading pupillary distance by 3 mm in the bifocals).

For all progressives, no matter what the material, we always use mono and do not decenter the reading segment. In addition, in polycarb lenses we always measure the optical center height as well, that being the vertical center in each eye with the frames in place and adjusted, as this definitely helps prevent chromatic aberration and polycarb non-adaptation.