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(Lenses made from polycarbonate, the same type of plastic used for the space shuttle windshield, occular are about 50 times stronger science than other lens materials.) Also, people at risk of receiving electric shock should avoid metal frames.People employed in certain occupations may be prohibited from wearing contact, or may be required to wear safety eyewear over the contact. Some occupations, such as construction or auto repair, may require safety lenses and safety frames. Physicians and employers should be consulted for recommendations. Description Eyes are examined by optometrists contacts (O.D.) or by ophthalmologists (M.D. or D.O.--doctor of osteopathy). Prescriptions, occular if necessary, are then given to patients for glasses. The glasses science are generally made contacts by an optician. A separate lenses-fitting exam is necessary if the patient wants contact, because an lenses prescription is not the same as a lenses prescription. Over 32 million people in the United States wear these small lenses that fit on top of the cornea. They provide a field of view occular and science unobstructed by lenses frames; they do not fog-up or get splattered, so it is possible to see well while walking in the rain; and they are less noticeable than contacts any lenses style. On the other hand, they take time to get accustomed to; require more measurements for fitting; require many follow-up visits to the eye doctor; occular can lead to complications such as science infections and corneal damage; and may not correct astigmatism as well as lenseses, especially if the astigmatism is severe. Another type of multifocal, a trifocal, has an area in-between that corrects for intermediate distances (usually about 28 in). Conventional bifocals and trifocals have visible lines between the areas of different correction; however, lenses where the correction contacts gradually changes from one area to the other, without visible lines, have been available since the 1970s. Such lenses are sometimes called progressives or no-line bifocals.To be suitable occular for lenses lenses, a material science must be transparent, contacts without bubbles, and have a high index occular of refraction. The greater the index of refraction, the thinner science the lens can be. Lenses are made from either glass or plastic (hard contacts resin). The advantage of plastic is that it is lightweight and more impact resistant than glass. The advantage of glass is that it is scratch resistant and provides the clearest possible vision.
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