Understanding Astigmatism

For most people, common vision conditions are easily understood. Nearsighted people know they have trouble seeing in the distance without correction, but can see just fine up close. Farsighted people usually see well in the distance, but may need help in order to read a book or computer screen. However, astigmatism is a little more mysterious, even to people who know they have it.

In order to understand what astigmatism is, it’s worth taking a moment to explore how your eyes work. In a healthy human eye, light is reflected from objects, and enters the eye by passing through the clear, dome shaped cornea. That light is refracted, or bent and redirected, by the cornea. That light passes through the pupil, then through the eye’s natural crystalline lens, which refracts the light again. The twice-refracted light then strikes the retina, an area of photosensitive cells at the back of the eye. Those cells transmit information to the brain, which then interprets that information, giving us our sense of sight.




In eyes with naturally good vision, the cornea and lens combine to focus light exactly on the retina. This condition, known as emmetropia, means that the person has no prescription or refractive error (and therefore no astigmatism).

If the cornea is too steep in shape, or the eye is too long from front to back, the incoming light will converge at a point in front of the retina. This condition is known as myopia or nearsightedness, and people who are myopic usually have an easier time focusing on near objects than faraway ones.

Conversely, if the cornea is too flat in shape, or the eye is too short from front to back, incoming light will converge towards an imaginary point behind the retina. This condition is known as hyperopia or farsightedness, and usually makes it more difficult to see near objects than ones that are far away.

Astigmatism occurs when the cornea, rather than being a regular round or sphere-like shape, is steep in some parts and flat in others, similar to a football or the back of a spoon. This irregularity can lead to blurry vision at a variety of distances. Astigmatism sometimes occurs in an otherwise emmetropic eye, but is most often found in combination with myopia or hyperopia. Very slight amounts of astigmatism may not be very noticeable and require no correction, but moderate to severe astigmatism causes poor quality of vision. Eyeglass prescriptions can correct astigmatism, as can special contact lenses, known as toric contact lenses. However, anyone who has to wear them knows that toric contacts are expensive (usually at least twice as much as regular soft contacts) and often uncomfortable.




In the early days of laser refractive surgery, the laser platforms could not correct astigmatism, and in fact astigmatism was one of the most common reasons that prospective LASIK patients were turned away as non-candidates. Some laser systems still struggle correcting moderate to higher degrees of astigmatism. However, modern vision correction surgery, such as the wavefront-optimized LASIK and PRK performed at Hoopes Vision, is capable of correcting significant amounts of astigmatism. In March 1998, the Summit laser system was the first laser approved to correct astigmatism and Dr. Hoopes, Sr. is credited with performing the very first astigmatism correction in the United States after FDA approval.

Part of the thorough preoperative examination at Hoopes Vision involves detecting the presence and location of any astigmatism, through precise mapping of the cornea. The lasers can then be programmed to correct the patient’s astigmatism at the same time as his or her nearsightedness or farsightedness. The result is that a large majority of our patients with astigmatism report seeing better after LASIK than they ever did with their glasses or contacts.

If you have ever wondered if LASIK or PRK may be a good option for you, and especially if you were told years ago that your astigmatism made you a poor candidate for laser vision correction, please contact us! Our complimentary, no-obligation screening and consultation will let you know what your options are, and give you all the information you need in order to make an educated decision about your vision.









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