If you have ever looked at your glasses prescription and wondered what the numbers mean, you are not alone. A prescription is a short summary, in a standard format used by optometrists across Alberta, of how lenses need to correct your vision. Understanding the basics can help you compare an old prescription with a new one and know when to book an updated eye exam in Mill Woods, Edmonton.
Why Your Prescription Looks Confusing at First
A glasses prescription is not a pass or fail result. It is a measurement, in steps called dioptres, of the lens power needed for each eye. Your eyes are measured separately, so the numbers are often different on each side. Small changes of 0.25 are common and do not always mean your vision has changed a lot.
The Main Parts: SPH, CYL and Axis
SPH, short for sphere, is the main lens power. A minus sign means the lens corrects short-sightedness, so distance objects look clearer. A plus sign means the lens corrects long-sightedness, helping with focus for close work. If SPH says PL, plano, or 0.00, no spherical correction is needed for that eye.
CYL, short for cylinder, is extra power used to correct astigmatism, which happens when the front of the eye is shaped more like a football than a basketball. If this column is blank, you have no astigmatism correction in that eye. AXIS is a number from 1 to 180 showing where the astigmatism correction sits. Axis only appears if you have a CYL value.
Other Numbers You Might See: ADD and PD
ADD is additional power added to the bottom part of a lens for reading. It is common in progressive and bifocal lenses and often appears when you need separate help for close work.
PD stands for pupillary distance, the distance in millimetres between the centres of your pupils. This helps the lab place the centre of each lens in front of your eyes. PD can be one total number or two numbers, one for each eye.
What OD, OS and OU Mean
Most prescriptions use Latin abbreviations. OD means your right eye, OS means your left eye, and OU means both eyes. Some newer printouts simply use R and L. Always check which row you are reading, because mixing up right and left is an easy mistake.
Why a Prescription Is Not the Same as an Eye Exam
A prescription tells you what lenses you needed on the day it was measured, but it does not explain why your vision changed or whether your eyes are healthy. A comprehensive eye exam also checks eye health, including the retina and eye pressure, and looks for conditions that may have no early symptoms. Using an old prescription for new glasses can mean lenses that no longer suit daily tasks such as driving, computer work, and reading.
At Infinite Eyecare, at 4275 23 Ave NW in Mill Woods, Edmonton, we explain your prescription in plain language at your visit. We offer direct billing to most major insurers, and eye exams for children under 19 and seniors are covered by Alberta Health Care.
Book an Eye Exam in Mill Woods, Edmonton
If your prescription is out of date, your glasses are broken, or your vision does not feel as clear as it used to, booking an updated eye exam is a practical next step. Bring your current glasses and prescription if you have it, and we can compare the new measurement with the old one. To book, call Infinite Eyecare at 780-425-0003.
