Making Sense of Your Eyeglass Prescription

May 15, 2021

OK, you just had your regular eye exam and now you have a prescription for eyeglasses. But what the heck do the numbers on that prescription mean?

Since we’re all about your eyes at Millennium Park, in this last blog before an awesome Chicago summer (especially compared to last year’s!), let’s decipher that eyeglass prescription.

Your prescription

OK, at the completion of your eye exam, you received the above eyeglass prescription. Let’s break it down.

·      OD = Your right eye parameters

·      OS = Your left eye parameters

·      Sphere

This indicates the amount of lens power prescribed for nearsightedness or farsightedness, measured in diopters. This is basically the strength of magnification needed to get your eyes to 20/20. If your number has a minus sign (-) you’re nearsighted; if it has a plus sign (+) you’re farsighted.

·      Cylinder & Axis

These are your astigmatism numbers. A Cylinder and Axis is required to correct your astigmatism. This is a little complicated, using meridians of the eye, degrees, and such. Remember that if you have astigmatism, the shape of your cornea is more oblong (think football) than the normal round shape. This creates refractive errors all over your eye. Just know that these two numbers correct for those errors. Again, a minus sign indicates correction for nearsighted astigmatism, and a plus sign corrects for farsighted astigmatism.

·      Add

This is the added magnifying power applied to the bottom part of multifocal lenses to correct for presbyopia. The number appearing in this section of the prescription is always a “plus” power. This is used for reading glasses, progressive lenses, and bifocals. The number is the same for both eyes.

·      Prism

A prism number indicates the amount of prismatic power, measured in diopters, needed to compensate for any alignment problems in your eyes. Not many eyeglass prescriptions have a prism number.

·      Pupillary Distance (PD)

PD is the distance between the center of one pupil (the central black dot of your eye) to the center of the other pupil, measured in millimeters.

Now you’re an eyeglass prescription expert.

If you have any problems with your eyes, trust the overall eye experts at Millennium Park to treat it. Call us at (312) 996-2020 to schedule your appointment.


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