No, not O.S. / left eye
The prescription lists Sphere, Cylinder, Axis on first line.
Second line is Add (single vision so blank), O.C. and Dist P.D. Both of these have two values for each eye, identical in this case.
I assume it’s related to the P.D. (pupillary distance), and is 1.5 cm lower, but which should I use for Zenni Optical etc.?
From that I can tell, OC is optical center and more or less the same as PD, it’s the distance from one pupil to the other. If the numbers are different, it’s the distance from each pupil to the center of your face.
The optical center is the point on the lens where a light ray can pass through with no refraction. The PD and OC numbers on the prescription tell the optician where to place the optical center of the lenses within the frame so that the optical center is properly aligned with the client’s pupils. The PD number tells her how to align the lens horizontally, and the OC number (much more rarely used) tells her how to align the lens vertically. The exact procedure is rather technical. See, for example, this YouTube video on Vertical and horizontal decentration.
I was able to reach an optician and they said it was the optical/ocular center. But it doesn’t explain which I should use when ordering glasses. Zenni seems to use them interchangeably.
To clarify: they gave two numbers for each OC and PD or 4 total, so the distances are from the nose not across. I don’t have it in front of me, but I think the OC was 23/23 and the PD 24.5/24.5.
I was a certified optician for 15 years. O.C. does indeed stand for optical center. But O.C. placement normally has to do with where the centers are vertically with respect to the eye, and that depends on the frame. If the O.C.s need to be 2mm above or below the pupil, the only way to measure for that is by looking at the frame on the patient. More commonly they’ll need to be higher for one eye than the other to induce prism and correct double vision. With progressives vertical position of O.C.s is critical, because too high and you’ll have to drop your head and look up to see at a distance. Too low and you’ll have to raise your head and drop your eyes to see up close, and may not even be able get your eyes down to the full reading portion.
With lined bifocals or trifocals we’d occasionally have prescriptions that called for the O.C.s to be a certain height above the top line, sometimes different for each eye.
Thanks. For single vision (and a pediatric prescription), I’d be okay just giving the PD?
Not really. You’d be much better off getting the prescription filled by a qualified optician. There’s no way in hell I’d trust my child’s eyes to an online place. I’ve seen the kind of crap they sell too many times, and I also know from having been in the business that it’s not physically possible to verify that P.D.s and other measurements are correct without being face to face with the patient. The correct measurements are ultimately the dispenser’s responsibility, and I would have been fired on the spot if I’d blindly accepted what an optometrist - or more likely optometrist’s assistant - wrote down.