Common vision problems include nearsightedness, farsightedness, and astigmatism, which results in blurred vision in all directions. To correct these problems, two main types of lenses are used: Convex/Plus (+) lens for nearsightedness and Concave/Minus (-) lens for farsightedness.
For those who are nearsighted, distant objects are out of focus. Convex/Plus (+) lenses work by bending light towards the bottom and top of the lens to push the focal point to the retina. The retina is a layer at the back of the eyeball with cells that are sensitive to light.
Conversely, for those who are farsighted, close objects are out of focus. Concave/Minus (-) lenses spread light from the center of the lens and adjusts the focal point.
The plus or minus sign in the parentheses above appear on an eyeglass prescription to indicate the lens type.
Other important components of an eyeglass prescription include lens strength and lens shape. Lens strength is measured in diopters and indicates how much the light is bent. Lens shapes are either spherical, cylindrical, or compound. To better understand how to read an eyeglass prescription and for an example of optometrist shorthand, check out the infographic below.