Refractive Errors and Vision Correction
How does the human eye work?
Light rays are constantly traveling in the world around you. Some of these rays reflect off of objects and enter your eyes through your pupils, allowing you to see. But why is it that some people have perfect vision, while others need glasses? The key to seeing clearly is proper focus.
Light rays do not always travel in a straight line, they can be bent by certain substances, and the structures in your eye are designed to bend these rays in a very specific fashion. Lining the back of the eye is a light-sensitive membrane called the retina. Special cells in the retina, called photoreceptors, capture images, much like the way a roll of film does in a camera. In order for you to see clearly, incoming light rays must be precisely focused on this membrane.
The various components of your eye all work together to make this happen. The cornea (clear surface of the eye), is the first to bend the incoming light, and the natural lens inside the eye plays an important role as well, bending these rays further. Even the various fluids within the eye are designed to help the process along. Ideally, all the incoming light rays will come together at one point, and that point will be located on the retina. Unfortunately, that is not always the case.
What are refractive errors?
The bending of a light ray is also called refraction, and when the eye does not bend and focus these rays correctly, we call that a refractive error. There are many kinds of refractive errors, and different conditions can result from them, including nearsightedness (myopia), farsightedness (hyperopia), and astigmatism.
The overall shape of the eye is an important factor in refraction. If the eye is too long, incoming light rays will be focused on a point in front of the retina, and will be out of focus by the time they hit it. This results in myopia. If the eye is too short, the opposite happens, and the light rays will not have a chance to focus before they reach the retina. In this case, the patient would be farsighted.
The shape of the cornea is also essential for proper vision. If it is not perfectly spherical, light rays will be focused irregularly, causing astigmatism.
Higher-order aberrations, can also cause poor vision. These distortions can be caused by various defects in the vision system, including large pupils, scarring, trauma, dry eyes, and flaws in the curvature of the cornea or natural lens.
The most common treatment for nearsightedness and farsightedness is, of course, glasses and contact lenses. These lenses, when placed in front of the eye, bend incoming light rays, and assist the eye to achieve proper focus squarely on the retina. The strength of your prescription is determined by the degree of your refractive error, which is diagnosed by your eye care professional during your eye exam.
Another popular treatment for these conditions is refractive surgery, such as LASIK. During these procedures, surgeons use special techniques to reshape the cornea of the eye, changing the way it bends light. The end result is the same as with eyeglasses: the eye is able to focus light rays directly on the retina, for clear vision.
Glasses, contact lenses, and refractive surgery can also be used to correct astigmatism. Higher-order aberrations, which can cause symptoms such as glare, halos, and starbursts, can sometimes be corrected by special lenses called Wavefront lenses. Wavefront technology creates a unique map of your eyes, allowing lenses to be tailored to your specific needs.
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