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Laser refractive surgery

Author
Kraig S Bower, MD
Section Editor
Jonathan Trobe, MD
Deputy Editor
Janet L Wilterdink, MD

INTRODUCTION

Laser refractive surgery is becoming increasingly popular as people are turning to alternatives to traditional spectacles and contact lenses for vision correction. This review will briefly discuss the anatomy and principles behind visual problems and correction, and will provide an overview of laser refractive surgery.

ANATOMY OF THE CORNEA

The transparent cornea is about one-half millimeter thick and has five distinct layers. The epithelium is the most exterior layer providing the smooth refractive surface and barrier against infection. The function of Bowman's membrane, which lies beneath the epithelium and its basement membrane, is unclear. The stroma, made up of intertwining lamellae of collagen fibrils, provides structure and accounts for 90 percent of the corneal thickness. The endothelium and its basement membrane (Descemet's membrane) form the innermost layers. Endothelial cells, via an active sodium-potassium-ATPase pump, are responsible for the natural corneal dehydration necessary for corneal clarity.

REFRACTIVE ERROR

Refraction is the bending of light rays as they pass from one transparent medium to another medium of a different density. Refraction is measured in diopters (D). The refractive power of a lens is the reciprocal of its focal length in meters. (See "Visual impairment in adults: Refractive disorders and presbyopia".)

In emmetropia (an eye with normal vision), the focusing power of the cornea and lens is perfectly matched to the length of the eye. Parallel light rays from a distant object are brought into focus precisely on the retina and a clear image is perceived (figure 1).

Refractive errors occur when light rays entering the eye do not focus properly on the retina:

                                  

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Literature review current through: Nov 2016. | This topic last updated: Wed Apr 27 00:00:00 GMT 2016.
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