The primary responsibility of the eye is to focus light. Light rays must focus precisely on the retina in order for your vision to be clear. At the front of your eye, the cornea provides the bulk of the eye’s focusing power. Internally, the lens inside your eye fine tunes the light, contributing to your ability to read.
Understanding Your Prescription
Common vision problems include myopia, hyperopia, astigmatism, and presbyopia. The degree of these vision problems are measured in units called diopters. A diopter is used to describe the light bending properties of an optical system. Glasses that correct for nearsightedness are expressed as a negative (-) number and as a positive (+) number for farsightedness. The more nearsighted, farsighted or astigmatic you are, the higher your prescription in diopters.
Your prescription is composed of three numbers:
For example,-5.00 -1.50 x 180 represents a typical prescription to correct a common vision problem.
- First Number: -5.00 identifies your degree of nearsightedness or farsightedness. The sign identifies whether you are nearsighted (- sign) or farsighted (+ sign).
- Second Number: -1.50 identifies your degree of astigmatism. The number can be written either with a + sign or a – sign.
- Third Number: 180 identifies the axis, which indicates the direction of your astigmatism. An axis of 180 degrees, for example, means the astigmatism is horizontal.
Therefore, a prescription of -5.00 -1.50 x 180 indicates that the patient is moderately nearsighted, with a moderate degree of astigmatism in a horizontal direction.