Know your prescription

If you wear eyeglasses or contacts, you’ve probable looked at your prescription at least once and wondered what it all means. To help clear up any confusion regarding what your eyeglasses prescription really means, it is important to understand a few basic words and abbreviations that can be found on the prescription.

1. Spherical Power

The sphere or spherical component of a spectacle prescription indicates the degree of hyperopia (farsightedness) or myopia (nearsightedness) in the axis meridian of an eye.  Plus (+) power indicates hyperopia, while minus (–) power indicates myopia. 

2. Cylindrical Power

The cylinder or cylindrical component of a spectacle prescription is an indication of the amount of astigmatism in an eye. Astigmatism is the amount that the refractive structures of the eye (primarily, the front and back surfaces of the cornea and the front and back surfaces of the crystalline lens) vary or deviate from sphericity or a spherical shape.  That is, astigmatism indicates the degree of toricity or cylindrical shape of all of the eye’s refractive components, combined. Cylinder values can be positive or negative.

3. Pupillary Distance

Pupillary Distance (PD) is the distance between the center of the pupil of each eye in millimetres. This value differs for left and right eye. This information is essential to ensure that the center of focus of your prescription glasses is in alignment with your pupils while making your glasses to enhance your vision. PD varies from person to person.

4. Astigmatism

Astigmatism is a vision condition that occurs when the front surface of the eye, the cornea, is slightly misshapen. This prevents the image of an object from focussing accurately on the retina. As a result, vision remains blurred at all distances. Astigmatism may accompany near sightedness or farsightedness. People with severe astigmatism will usually have blurred or distorted vision. While those with mild astigmatism will experience headache, eyestrain, fatigue or blurred vision at certain distances.