About 45 million Americans wear contact lenses. About 9 out of 10 people who wear contact lenses use soft lenses. In general, there are 2 types of contact lenses:. A contact lens prescription includes more information than an eyeglass prescription. Special measurements are taken of the curvature of the eye. In addition, your child's healthcare provider will determine if their eyes are too dry for contact lenses.
The provider will also see if there are any corneal problems that may prevent your child from wearing contact lenses. Trial lenses are often tested on the eyes first to ensure the correct fit. Eye care specialists are required by federal law to give you a copy of your contact lens specifications.
Parents know they need to protect their children's skin from harmful sun rays. But many forget that the eyes need to be protected, too. Sun exposure may set children up for possible vision problems later in life. The sun can cause sunburned corneas, cancer of the eyelid, cataracts, and macular degeneration, among other problems. Children also tend to spend more time outdoors than their parents, often in places where there is a lot of sun reflection. These include beaches, pools, and amusement parks.
It is also important for your child to wear sunglasses in the snow as well. Most UV eye damage is the result of years of exposure. Buy your child sunglasses that block both kinds of UV rays. Make sure the sunglasses fit correctly and are comfortable. Search Encyclopedia. Eyeglasses and Contact Lenses Lenses for correcting or improving vision There are 2 types of lenses prescribed for correcting or improving vision.
These include: Eyeglasses. How to read an eyeglass prescription The lens power of eyeglasses is measured in diopters. When looking at an eyeglass prescription, you will see the following abbreviations: OD Oculus dexterous. 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. Correcting Nearsightedness What power of spectacle lens is needed to correct the vision of a nearsighted person whose far point is Strategy You want this nearsighted person to be able to see very distant objects clearly. Discussion The negative power indicates a diverging or concave lens, as expected.
Example 2. Correcting Farsightedness What power of spectacle lens is needed to allow a farsighted person, whose near point is 1. Strategy When an object is held Conceptual Questions It has become common to replace the cataract-clouded lens of the eye with an internal lens.
This intraocular lens can be chosen so that the person has perfect distant vision. Will the person be able to read without glasses?
If the person was nearsighted, is the power of the intraocular lens greater or less than the removed lens? If the cornea is to be reshaped this can be done surgically or with contact lenses to correct myopia, should its curvature be made greater or smaller? Also explain how hyperopia can be corrected.
If there is a fixed percent uncertainty in LASIK reshaping of the cornea, why would you expect those people with the greatest correction to have a poorer chance of normal distant vision after the procedure? A person with presbyopia has lost some or all of the ability to accommodate the power of the eye. What is the near point of a person whose eyes have an accommodated power of What is the range of diopters for spectacle lenses that this person might need after LASIK procedure?
How do you know? What was the previous far point of a patient who had laser vision correction that reduced the power of her eye by 7. A severely myopic patient has a far point of 5. By how many diopters should the power of his eye be reduced in laser vision correction to obtain normal distant vision for him? How far is the board from his eyes? How far from her eyes is the feature being examined?
A young woman with normal distant vision has a What is the closest object she can see clearly? The far point of a myopic administrator is A very myopic man has a far point of What power contact lens when on the eye will correct his distant vision?
This is why the eye is called farsighted. In this exercise, we want to pick which type of lens, either convex or concave, can correct farsightedness. This means we want to know which kind of lens will fix this problem, the problem that a farsighted eye cannot clearly see objects that are near to the eye. Recall that a concave lens looks like this. The sides of this lens curve inward toward one another. When parallel light rays reach a concave lens, the lens causes the rays to spread out from one another.
As we look at our farsighted eye though, notice that the rays are already too spread out, we could say. To bring them to a focus, we want them to meet at the retina. That is, we want to bend them more towards one another, not less.
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