An essential element when fitting sunglasses is the reduction of sunlight (ultraviolet A and B) into the eye from the top or from the side of the eyeglass frames. With the entire unique facial configuration, find the shape of the lens that provides thorough coverage of "eyes" is very important.
You have noticed that to fit the curved lens into the frame sunglasses, the frames have a much more aggressive than the curvature of reading glasses. A higher base curve means a lens that is curved, wrap around the face to provide coverage for the eyes. Reading glasses provide basic curves zero, while the standard glasses provide 8 curves based. You can check this out to buy sunglasses.
Sunglasses frames come in various widths. A-frame that is too wide will allow ambient light to enter from the side and above. Instead, the frame is too comfortable to be uncomfortable during extended wear.
Most people prefer the lighter weight and feel while wearing sunglasses, usually determined by the weight of the lens material, the thickness of the lens, and frame materials selected. Professional glasses will help ensure the correct conformity.
Lens Materials – Four Primary Materials
Two values are used to determine the optical clarity of the lens material. Aberrations or Abbe value and the index of refraction, measurement ridiculously complex that includes long-wave ultraviolet speed, light refraction, and the dispersion of light refracted through different lens materials. For our purposes, we will use to determine the value of Abbe optical clarity material.
Superior optics, but heavy and can shatter on impact
An industry standard for 30 years, polycarbonate is very durable and cheap, but it has the largest number of optical lens distortion unless corrected. Polycarbonate is generally thinner and lighter than CR-39.
Heating and bending the lens material to match the special glasses frames cause distortion. To improve this quality optics, the lens "center ground" or "de-cantered", which means the lenses are usually thinner in the middle and thick around the lens. Optical lenses correct glasses also called aspheric lenses.