Thursday, March 12th, 2009
Ophthalmology Explained: What are those numbers in an eyeglasses prescription?
After visiting the Ophthalmologist yesterday, I received a prescription for corrective lenses with some crazy numbers on it. It looked something like this:
SPH CYL AXIS
O.D.: -1.00 +0.75 180
O.S.: -1.25 +0.75 165
What does all that mean? I turned to the Wikipedia explanation for answers.
It turns out that this is a precription for distance vision only (near vision corrections are usually not necessary for a 25-year-old).
What are the abbreviations?
- O.D. abbreviates oculus dexter, Latin for “right eye”
- O.S. abbreviates oculus sinister, Latin for “left eye”
- SPH stands for spherical diopter units
- CYL stands for cylindrical diopter units
- AXIS defines the angle of the CYL correction in degrees
The spherical component is the main correction as it acts equally to correct blur in all directions. The cylindrical component corrects blur in only one direction — therefore it is useful in correcting astigmatism. The axis angle defines the direction of the necessary cylindrical correction.
Addenda (2011 April 24):
In addition, my pupillary distance is 65 mm. This distance from pupil center to center is useful for ordering glasses online (such as at Warby Parker).
