Understanding your Glasses Prescription

When you leave Carolina Ophthalmology with a new glasses prescription, it can be helpful to understand what the numbers indicate about the glasses you need and about your eyesight. When you look at the prescription, you will see two sets of numbers under the headings of OD and OS. They are abbreviations from the Latin forms of right and left eye.

OD (Oculus Dextrus) means right eye

OS (Oculus Sinister) means left eye

Without Astigmatism:

  

For people who have no astigmatism (spherical eyes), there will be one number for each eye. This number is known as the sphere portion of the prescription. The farther away from zero this number is, the worse your eyesight is, and the more correction your lenses will employ. A plus sign in front of this number indicates you are farsighted (need glasses to see up close) and a minus sign in front of the number indicates you are nearsighted (need glasses to see far away). The number shows how many diopters, units that measure correction, your lens requires.

  

For example, if your glasses prescription read:

OD: -1.50

OS: -2.75

  

That would mean that your right eye has 1.50 diopters of nearsightedness and your left eye has 2.75. Another way to say it is that your right eye requires -1.50 diopters of correction and your left requires -2.75.

  

This indicates that you are nearsighted, and that your left eye requires more correction than your right.

With Astigmatism:

For people who have astigmatism (non-spherical eyes), there will be three numbers for each eye in your prescription.

The first number is the sphere, which is the number discussed above. This is the degree of nearsightedness or farsightedness.

The second number is the cylinder. This represents the amount of astigmatism measured in diopters. This can be a positive or negative number based on which type of measurement system your doctor uses. At Carolina Ophthalmology, we measure in plus cylinder, so it will have a plus sign in front of it. The bigger the number, the more astigmatism your eye has.

  

The third number is the axis. This number will be somewhere between 0 and 180 and is measured in degrees. It represents the orientation of your astigmatism.

For example, if your glasses prescription read:

                                OD: -3.00 +1.50 x 045

                                OS: -3.50 +2.00 x 105

That would mean that your right eye has 3.00 diopters of nearsightedness with 1.50 diopters of astigmatism at an axis of 45 degrees. Your left eye has 3.50 diopters of nearsightedness with 2.00 diopters of astigmatism at 105 degrees.

Your left eye would require more correction than your right. It has both more nearsightedness and more astigmatism.

Call us today to schedule an appointment to come in and get a new glasses prescription!