How can nearsightedness and farsightedness be corrected

Check each of your eyes separately by looking at the center cross without spectacles if you wear them. If lines along some axes appear darker or clearer than others, you have an astigmatism.

Another common vision defect is astigmatism , an unevenness or asymmetry in the focus of the eye. For example, rays passing through a vertical region of the eye may focus closer than rays passing through a horizontal region, resulting in the image appearing elongated. This is mostly due to irregularities in the shape of the cornea but can also be due to lens irregularities or unevenness in the retina.

Because of these irregularities, different parts of the lens system produce images at different locations. The eye-brain system can compensate for some of these irregularities, but they generally manifest themselves as less distinct vision or sharper images along certain axes. Figure 4 shows a chart used to detect astigmatism. Astigmatism can be at least partially corrected with a spectacle having the opposite irregularity of the eye. If an eyeglass prescription has a cylindrical correction, it is there to correct astigmatism.

The normal corrections for short- or farsightedness are spherical corrections, uniform along all axes. Contact lenses have advantages over glasses beyond their cosmetic aspects. One problem with glasses is that as the eye moves, it is not at a fixed distance from the spectacle lens.

Contacts rest on and move with the eye, eliminating this problem. Because contacts cover a significant portion of the cornea, they provide superior peripheral vision compared with eyeglasses. Contacts also correct some corneal astigmatism caused by surface irregularities. The tear layer between the smooth contact and the cornea fills in the irregularities. Since the index of refraction of the tear layer and the cornea are very similar, you now have a regular optical surface in place of an irregular one.

If the curvature of a contact lens is not the same as the cornea as may be necessary with some individuals to obtain a comfortable fit , the tear layer between the contact and cornea acts as a lens. If the tear layer is thinner in the center than at the edges, it has a negative power, for example. Skilled optometrists will adjust the power of the contact to compensate. Laser vision correction has progressed rapidly in the last few years. It is the latest and by far the most successful in a series of procedures that correct vision by reshaping the cornea.

As noted at the beginning of this section, the cornea accounts for about two-thirds of the power of the eye. Thus, small adjustments of its curvature have the same effect as putting a lens in front of the eye. To a reasonable approximation, the power of multiple lenses placed close together equals the sum of their powers. So to correct the eye for nearsightedness, the cornea is flattened to reduce its power.

Similarly, to correct for farsightedness, the curvature of the cornea is enhanced to increase the power of the eye—the same effect as the positive power spectacle lens used for farsightedness.

Laser vision correction uses high intensity electromagnetic radiation to ablate to remove material from the surface and reshape the corneal surfaces. Figure 5. The upper corneal layer is temporarily peeled back and minimally disturbed in LASIK, providing for more rapid and less painful healing of the less sensitive tissues below.

The top layer of the cornea is surgically peeled back and the underlying tissue ablated by multiple bursts of finely controlled ultraviolet radiation produced by an excimer laser. Lasers are used because they not only produce well-focused intense light, but they also emit very pure wavelength electromagnetic radiation that can be controlled more accurately than mixed wavelength light.

The nm wavelength UV commonly used is extremely and strongly absorbed by corneal tissue, allowing precise evaporation of very thin layers. A computer controlled program applies more bursts, usually at a rate of 10 per second, to the areas that require deeper removal.

Typically a spot less than 1 mm in diameter and about 0. The corneal flap is replaced; healing takes place rapidly and is nearly painless. Skip to main content.

Vision and Optical Instruments. Search for:. Vision Correction Learning Objectives By the end of this section, you will be able to: Identify and discuss common vision defects. Explain nearsightedness and farsightedness corrections. Explain laser vision correction. Example 1. Those who spend considerable time reading, working at a computer, or doing intense close visual work are more likely to develop myopia.

LASIK does an excellent job of correcting nearsightedness. Also called hyperopia, farsightedness is the inability to see near objects as clearly as distant objects. Common signs of hyperopia include difficulty concentrating and maintaining a clear focus on near objects, eye strain, and fatigue.

LASIK is a great option to correct this condition. Astigmatism is a relatively common eye condition involving an irregular curvature of the cornea. Physical irregularities in the cornea cause distortion of the viewed image on the retina. As a result, vision becomes blurred or doubled at any distance, and can lead to eye discomfort and headaches. During your consultation, our highly-trained team will determine your eye condition and let you know which procedures might be suitable.

We offer multiple procedures so our doctors can match your eyes with the correction option that they think will provide the best outcome for your vision and you may have options. Schedule a consultation and get yourself on the path to better vision today! If you have blurry vision at both near and far distances, the odds are that you have astigmatism , which can also be corrected by LASIK or corrective lenses.

A farsighted LASIK patient goes through roughly the same process as a patient with nearsightedness or astigmatism. Finally, the surgeon puts the tissue flap back in its original place, where it heals mostly within the next few hours. LASIK eye surgery for farsightedness may not be suitable for people with high levels of hyperopia, thin corneas or other health considerations.

Here are a few of the methods typically used:. Modern LASIK for reading can correct vision problems caused by presbyopia with a technique called monovision LASIK , where an eye surgeon fully corrects the vision in one eye and intentionally leaves the other eye a little nearsighted. The corrected eye will then see distant objects very clearly, while the nearsighted eye provides sharper near vision without corrective lenses.

That might sound strange at first, but the human brain is very good at adapting to changes like this.