THE HUMAN EYE AND HOW VISION WORKS
UNDERSTANDING YOUR EYEGLASS PRESCRIPTION
Your eyeglass prescription is written in numbers. The type and degree of refractive error is quantified in units of measure called diop ters. If you have ever wondered what those numbers mean, here is how to read and understand your prescription.
To arrive at your prescription, your doctor takes three measurements during the eye exam: sphere, cylinder, and axis. Your prescription for glasses may look something like this:
OD -1.25 - -
OS -1.25 - .25 - 170
OD and OS refer to the right and left eyes, respectively. The first number next to OD or OS represents the sphere. The sphere measure tells the eye doctor where your eye focuses light: on the retina (normal vision), in front of the retina (myopia), or behind the retina (hyperopia). In other words, the sphere measure reveals whether you are nearsighted or farsighted. A negative diopter indicates myopia, or nearsightedness. A positive diopter indicates hyperopia, or farsightedness. The higher the number, the stronger the prescription. In the example above, the person has mild myopia (-1.25 diopters) in both eyes.
The number in the second column represents the cylinder. The cylinder measure indicates whether or not the patient has astigmatism. If the cylinder column is not blank, you have some degree of astigmatism. The larger the number, the more astigmatism you have. The example above reveals that this person has no astigmatism in the right eye, and a small amount (-.25 diopter) in the left eye.
If astigmatism is present, your eye doctor takes an axis measurement. The axis measure indicates where irregularity lies on the eyeball. In the prescription above, the astigmatism in the left eye is positioned at the 170-degree axis.
Nonsurgical Vision Correction Options
