How to read your glasses prescription (SPH, CYL, AXIS, PD)

Your glasses prescription is three or four abbreviations and a grid of numbers — and once you can read it, you'll never feel lost in an optical shop again.

The columns

• SPH (Sphere)
• CYL (Cylinder) — the correction for astigmatism, if you have it. Often blank or 0.00.
• AXIS — the orientation of the astigmatism correction, from 0 to 180 degrees. Meaningless without CYL.
• ADD (Addition) — extra power for reading, present on prescriptions for progressive or bifocal lenses. Usually the same in both eyes.
• PD (Pupillary Distance) — the millimetres between your pupils. Needed to centre the lenses correctly.

Reading an example

Take: SPH −2.50, CYL −0.75, AXIS 180. That's moderate short-sightedness with mild astigmatism at a horizontal orientation. Take: SPH +1.00, ADD +2.00 — long-sightedness with a reading addition, typical of a progressive-lens prescription for someone in their 50s.

The two practical traps

1. Don't mix up sign conventions between countries. Prescriptions from different countries occasionally format cylinder signs differently (plus vs minus cylinder). If ordering lenses from a prescription written overseas, let the optician transcribe it — don't convert it yourself.
2. PD is usually not on the prescription. In Malaysia it's typically measured during dispensing. Ask for the number and record it — you'll want it for any future online ordering or spare glasses.

Keep your prescription

Photograph it and keep a note of your PD. It makes replacing lost glasses, ordering spares, or getting a second price quote trivial — and it lets you compare quotes between shops honestly. When you're ready to use it, every shop in the directory lists a phone number where available; call two or three in your town, read your prescription out, and compare what they quote you.