Cheap lens information
Prescription Lenses may be constructed with various coatings that enhance, optically and cosmetically, the pair of eyeglasses you buy. These coatings are thin films applied to the front and/or back of carbon or glass lenses. Among these coatings are Scratch Resistant Coating, Ultraviolet Treatment, Anti Reflective Coatings - as well as Polarized glasses - Tinted lenses, and mirror coatings.
Scratch Resistant Coating, when treated to the front and back of the lens, significantly prevents the lens from the inevitable abrasions suffered by glasses when they fall or are hit. No lens is ever scratch "proof", but the coating adds extra protection. Polycarbonate lenses, in particular, are sold with scratch resistant coating free of charge (the polycarbonate, naturally soft and lightweight, would scratch too easily without it).
Anti-Reflective coating is another highly useful coating designed primarily to decrease glare. This makes driving at night much safer. It also decreases reflection and light halos and, cosmetically, allows the face to be seen clearly as it prevents distracting light from bouncing off the lenses. This is particularly useful for High Index lenses and for sunglasses: when applied to the back of the lens, it prevents light from bouncing off the back-lens and into the eyes. It should be noted that many sunglasses are put through a process called "polarization", which is another method of decreasing glare. Polarization allows only vertically polarized light to enter the glasses, so that any light that reflects off horizontal surfaces like lakes or car hoods does not pierce into the wearer's eyes. (The effect of polarization is similar to the adjusting of a venetian blind - the light still shines through the room, but not directly into you)
The Ultraviolet filter, an important coating, cuts down on dangerous ultraviolet rays shining into the eyes and face. Overexposure to UV rays is harmful to the eyes, as well as the skin, and has been linked to retinal damage and cataracts. This coating is inexpensive and easily applied to lenses -- except to polycarbonate lenses, which happen to be naturally UV resistant. Photochromic lenses - designed for sunglasses - are unique lenses that become lighter or darker in proportion to their exposure to UV light.
Mirror coatings, still another type of coating, are purely cosmetic in nature because the wearer perceives no visual difference. They are designed to reflect only external images. In other words, a person looking at you could see his/her reflection in your glasses! Mirror coatings are designed for sunglasses, like those worn by State Troopers, or for colored lenses. These may be pretty much any color - blue, pink, you name it. (Color tints can be applied to both glass and plastic lenses, the latter through a process of absorption - the former through a coating process).
As always, you should consult your Optician before or during the purchase of any type of eyeglasses; and, be sure to consult with your Opthalmologist, and then with the Optometrist, for the best eye care.
