Prescription eyewear

Prescription Eyewear and Glasses

Glasses were originally made from glass, but many are now made from plastic (often polycarbonate or CR-39) due to the danger of breakage and the greater weight of glass lenses. Some plastics also have more advantageous optical properties than glass, such as better transmission of visible light and greater absorption of ultraviolet light. Some plastics have a greater index of refraction than most types of glass, allowing thinner lenses for a given prescription. Scratch-resistant coatings can be applied to most plastic lenses giving them similar scratch resistance to glass. Hydrophobic coatings designed to ease cleaning are also available, as are anti-reflective coatings intended to improve night vision and make the wearer's eyes more visible.

Corrective spectacles have lenses shaped to correct vision abnormalities, such as myopia.

Corrective lenses modify the focal length of the eye to alleviate the effects of shortsightedness (myopia), longsightedness (hyperopia) or astigmatism. The power of a lens is generally measured in diopters. Over-the-counter reading glasses are typically rated at +1.00 to +3.00 diopters. Glasses correcting for myopia will have negative diopter strengths. Lenses made to conform to the prescription of an ophthalmologist or optometrist are called prescription lenses and are used to make prescription glasses.

Glasses are often regarded as unattractive, and many people prefer to wear contact lenses for that reason. Contact lenses also provide much improved peripheral vision.

On the other hand, many people are attracted to people who wear glasses, and glasses are available in a wide range of styles, materials, and even designer labels.

Glasses can be a major part of personal expression, from the extravagance of Elton John and Dame Edna Everage, from Groucho Marx to John Denver to Lisa Loeb all the way to the varied professional personas of eyeglass-wearing knowledge workers.

Sun Glasses

Sunglasses may be made with either prescription or non-prescription (i.e. plano) lenses that are darkened to provide protection against bright visible light. Good sunglasses should also protect against ultraviolet light. Due to changes in the atmosphere, ultraviolet levels are much higher than in the past and ultraviolet protection for eyes and skin is even more important. It is possible to have lenses that look very dark and yet offer little ultraviolet protection. Sunglasses vary greatly and many offer more style than protection.

Glasses with photosensitive lenses, called photochromic lenses, become darker in the presence of UV light. Unfortunately, many car windshields protect the passengers from UV light, while not shielding from bright visible light, making photochromic lenses ineffective where they are most needed. Still, they offer the convenience of not having to carry both clear glasses and sunglasses to those who frequently go indoors and outdoors during the course of a day.

Light polarization is an added feature that can be applied to sunglass lenses. Polarization filters remove horizontal rays of light, which can cause glare. Popular among fishermen and hunters, polarized sunglasses allow wearers to see into water when normally glare or reflected light would be seen. Polarized sunglasses may present some difficulties for pilots in that reflections from water and other structures often used to gauge altitude may be removed, or instrument readings on liquid crystal displays may be blocked.

Site Index by Category

Allergy Relief

Allegra

Flonase

Nasacort

Nasonex

Zyrtec

Antibiotics

Augmentin

Amoxicillin

Bactrim

Biaxin

Cephalexin