||Correcting Your Vision
With Glasses and Contacts
Glasses and contact lenses correct refractive errors by
adding or subtracting focusing power to your cornea and
lens. The power needed to focus images directly on your
retina is measured in diopters. This measurement is also
known as your eyeglass prescription.
If you have myopia, your cornea and lens have too much
focusing power, bending light rays to meet at a point in
front of the retina. Glasses and contacts compensate for
this condition by subtracting power from the eye's natural
focus and allowing light rays to focus further back on the
retina. If you have myopia, your prescription will be
negative, for example, -4.25 diopters.
If you have hyperopia, glasses and contacts add focusing
power, causing light rays to bend more as they enter the
eye. This process moves the focal point back to the retina,
allowing for clear vision. If you have hyperopia, your
prescription will be positive, for example, +4.25
If you have astigmatism, the shape of the glass lens
compensates for the uneven corneal curve and focuses the
light rays to a single point on the retina.