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The eye’s surface is convex. Light rays first pass through the clear cornea on the surface, then through the lens located inside of the eye, where they bend toward its center. In an eye that has a normally curved cornea and the correct shape, an image focuses exactly on the retina to produce normal “perfect” vision, also called “emmetropia.”

Vision issues(refractive errors) are caused when the curvature of our cornea is either too steep, flat or uneven to focus the light rays onto the retina and they are instead focused in front of or behind the retina or at multiple points. 

Scroll down through the common refractive errors below to learn more:


Nearsightedness (myopia)

When the eyeball is too long, light rays focus in front of, rather than on the retina. Under these circumstances, near objects are perceived clearly, but distant objects are not.

Farsightedness (hyperopia)

When the eyeball is too short, light rays entering the eye focus behind the retina. Distant objects are seen clearly, but near objects are not.


Vision becomes distorted when the surface of the cornea has an uneven curvature. Sometimes it is the eye’s lens that is irregularly shaped. This type of irregularity causes light to focus on more than one spot of the eye, resulting in blurred vision.

Presbyopia (loss of reading vision)

Over time, the eye’s lens gradually loses its elasticity and its ability to change shape (“accommodate”) to see close objects. Bifocals or reading glasses are the traditional prescription for remedying this presbyopic loss of accommodation, but newer technology makes it possible to exchange the inflexible lens for one designed to compensate for changes in the eye and improve functional vision at all distances.

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