What Is a Refractive Error?

This is the term used to denote an error in eye focusing that produces blurred vision. If the combination of eye focusing elements (the cornea and internal crystalline lens) do not focus the visual image precisely upon the retina, the result is poor vision. Up to now we could only compensate for these errors in focusing by prescribing glasses or contact lenses to assist the eye in it’s focusing. With the advent of laser vision correction and ICL implants, we can now obtain the same corrective effect by modifying the shape of the cornea.

What Is the Cornea?

The cornea is the clear focusing lens at the front of the eye that provides the greatest percentage image resolution, upwards of 70%. Working in conjunction with the eye’s internal focusing element, the crystalline lens, the cornea allows for the placement of a clear visual image upon the retina. Visual elements within the retina will then process the image and send it on to the brain for interpretation. The cornea is made up of orderly layers of collagen strands known as lamellae. These lamellae are arranged in arrays that are precisely separated by a chemical family of ground substance known as glycosoaminoglycans. It is this orderly arrangement of fibers, in conjunction with the cornea’s inherent low water content that allows for its optical clarity. The shape of the cornea is modified when we treat errors in eye focusing (aka refractive errors) with the excimer laser. The central cornea is flattened to address myopic and astigmatic errors and steepened to correct hyperopic errors.

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