What is myopia, hyperopia, astigmatism, and presbyopia?
Refractive errors are optical defects of the eye classified as nearsightedness (myopia), farsightedness (hyperopia), and/or astigmatism. Just like weight is measured in pounds, refractive error is measured in its own unit called diopters (D). The smallest amount of optical power typically measured during an eye examination is 0.25 D.
Myopia (nearsightedness) is the most common refractive error corrected by LASIK. In myopia the eye is usually too long. Therefore, light from distant objects focuses in front of the retina causing blurry vision. As an object is brought toward the eye, the focus of light in the eye moves back and at some point focuses on the retina. Hence the person sees better at near than at far.
Hyperopia (farsightedness) is actually more common than myopia. In hyperopia the eye is usually too short and light therefore is coming to a focal point behind the retina. In mild cases of hyperopia, younger people can focus their eyes and bring the focus "forward" in the eye to see clearly. However, in more severe cases, this causes too much eyestrain and glasses are needed. Because it is easier for a hyperopic person to focus at distance than at near, they are called farsighted.
Mild amounts of astigmatism are very common, but larger amounts can cause symptoms of blurred vision or eyestrain. Astigmatism is usually caused by the cornea of the eye having an unequal curvature in each of its meridians as opposed to a spherical shape (like a basketball). This unequal curvature is similar (but not as extreme) to the shape of one side of a football. Therefore, each meridian of the cornea focuses light at a different point and causes blurred vision.
Presbyopia is an eye problem that begins to show in everyone sometime after the age of 40. This problem is due to a gradual loss of focusing ability of the eye and requires reading glasses or bifocals for its correction. Currently there are no refractive surgery procedures that correct this problem. If a person has successfully worn contact lenses using monovision (one focused at distance, one for near), they may be able to be corrected for monovision with LASIK. Other procedures like LTK or CK do not correct presbyopia. The advertising campaigns surrounding these procedures imply that they do, but the advertising is misleading.
LASIK is an outpatient surgical procedure that changes the shape of the cornea to correct these refractive errors. During LASIK a flap of cornea is created with a device called a microkeratome. This flap is then lifted back so that the laser can sculpt the cornea underneath in a fashion to correct the refractive error(s). The flap is then carefully repositioned. Because the front surface of the flap, called the corneal epithelium, is minimally disturbed, the patient usually has a rapid recovery of vision and minimal discomfort during the post-operative period.
Although the procedure only takes a few minutes and is outpatient, LASIK is permanent and cannot be undone. We are, after all, talking about the quality of your vision for the rest of your life. It is very important to choose the right surgeon, the right support staff, and the right laser. If you would like to schedule a no cost, no obligation consultation, call our office at