HomeFAQsHow do eye glasses improve a persons sight?

How do eye glasses improve a persons sight?

People wear glasses if their vision is blurry, because glasses make the vision clear. First, let me explain how the eye works. The eye is similar to a camera which uses a lens to focus an image on film. The eye contains the cornea, the clear outermost layer, and the lens, which is a round tissue in the middle of the eye. Light passes first through the cornea, pupil (the black opening in the colored part of the eye) , the lens, and onto the retina, which is the lining or “film” in the back of the eye. The cornea and lens focus an image onto the retina, which, in turn, converts the light into electrical signals which go to the brain. The lens projects an upside-down image onto the retina much in the same way that a camera lens projects an upside-down image onto film. Your brain adjusts this so that we see the image right-side-up.

The cornea and lens must bend the light rays as they enter the eye in order to focus the image onto the retina. The eye can focus on objects at different distances by having the lens change shape to vary the amount of bending of light.

A refractive error occurs when the cornea and lens are unable to correctly focus the image on the retina. Myopia occurs when the eye is longer than normal, or when the cornea is more curved than normal. In myopia, the light rays focus in front of the retina. Hyperopia occurs when they eye is shorter than normal, or when the cornea is flatter than normal. Here, the light rays focus behind the retina. Presbyopia occurs sometime after the age or 40, when the lens is less and less able to change shape to focus up close . Astigmatism occurs when the cornea is not round but is more football-shaped. The light rays are unable to focus onto a single point.

For myopia, a concave or “minus” lens is used to “unbend” the light rays and thus move the focus further back into the eye so as to properly place the image onto the retina. In hyperopia, a convex or “plus” lens is used to add extra bending and pull the focus back toward the lens and onto the retina. Presbyopia involves the use of reading glasses, which also utilize a convex lens. In each of the above situations, appropriately-powered lenses in the glasses change the bending of the light rays to adjust the focus back onto the retina.


Nancy Oplinger

  • M.D, Private Practice in opthamology in Auburn

Bachelor’s from Hamilton College; M.D. New York Medical College; residency in opthamology with New York Medical College
Research Area:
Husband: Thomas Arias, physicist at Cornell and daughters Liliana and Francesca
Spending time with family, classical music, outdoor activities, skiing

Question From

Teresa Ober
Ithaca High School
Ms. Gefell
Future Career:
Science Teacher

Powered By: AcademicsWeb