Changes in the shape and size of your eyes can cause problems that affect the way you see things that are close up or far away. These problems are referred to as refractive disorders. Refractive disorders include myopia (nearsightedness), hyperopia (farsightedness), presbyopia, and astigmatism. This section will help you to understand these disorders and what they might mean to you.

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The curvature of your eye is measured in diopters (D) - a unit of measurement used by doctors to determine the severity of vision problems. This measurement becomes your prescription. For example, if you're farsighted, you may require a distance correction of +1.25 D. If you're nearsighted, you may require a distance correction of -1.25 D. Why is one a "plus" and the other a "minus"? The answer is in this section. Read on.