Sunglasses

Now how do you ensure that you sunglasses have UV protection. One thing is to buy from reputed people who are aware of the UV problem and take their advice. Very few outlets in India have a UV check instrument that the buyer can use to his advantage. In case of dark lenses it is imperative that a UV blocker be incorporated. In a dark glass, the amount of visible light coming to the eyes is reduced. In such a situation, the pupils of the eyes become wide to allow as much light in as possible. Along with the extra visible light the unfiltered UV light also enters the human eye thus increasing the concentration of UV rays inside the eyes. In that case, dark glasses cause damage to the eyes rather than protecting them. But in the presence of a UV blocker, the UV would be filtered at the very surface of the lens and what will enter the dilated pupil will be only visible light. That makes it necessary to check for the UV block in a sunglass lense.

UV Protection is hyped and all and we feel secure in the knowledge of the availability of eye-wear / sun-wear to bail us out. But what about the Infra-Red (IR) rays that come at the other end of the visible spectrum? These rays bring with them a sensation of warmth which over a long period of time can cause clouding of the transparent ocular structures leading to cataract. Staring straight at the sun can cause a burn in the most sensitive part of the retina called the macula. The Calobar (green) shade of the good old days is still the winner against IR protection lenses.

There is a small band of UV rays between 280 and 300 nm which have damaging effects on the eyes. Most of these are absorbed by the frontal adnexa of the eyeball like the skin of lids, conjunctiva and cornea. But some amount of the UV rays enters the eye through the pupil along with the visible light. The inner structures like the crystalline lens and the humors further absorb a chunk of the UV light and it reaches the retina only in small amounts. Long term exposure to UV rays causes itching sensation around the eyes, watering eyes, photophobia, swelling of conjunctiva, puffiness in around the eye lids, delayed dark adaptation. Long term exposure to UV rays has been implicated as one of the causes for cataract formation.

What is this ho-hullo about the UV thing?
The rays of the sun contain a spectrum of rays with various wavelengths. The light that we see is a small part of the spectrum from 400nm to 800 nm roughly. The rays less than 400 nm are the once we cannot see and are called Ultra-Violet rays or UV for short. Similarly the wavelengths beyond 800 nm are Infrared Rays.

Ultra-Violet Protection

Tips
Since styles change with time, here are a few points that may help you while you select a good pair of sunglasses for yourselves. Check if the frame covers most of the region around the eyes. Thicker temples can act as mechanical shields on the sides. Though not every pair of sunglasses can be verified for its UV Protection, try buying it from stores who have a proven track record of honest dispensing.

Polarising Lenses
Another technological advancement that few are aware about and which serves as both anti-glare solution as well as a dark glass is polarizing lenses. The biggest advantage of polarizing lenses is that they cut out glare caused by reflections from the tarmac, hoardings, glass panels etc. This affords clearer vision through wind-screens and therefore an edge to drivers during afternoons. And now with opening of import policies you can cool your eyes with designer sunglasses from the world over or just settle for an economical indigenous brand.

Photochromic Lenses ( " Sunglasses" )
Photochromic lenses are generally useful for people who have to move in and out of the sun often. They have been a preferred choice of many people, especially those who have to move in and out a lot. But these lenses lose their efficiency when the temperatures reach the mid 40s. Also these lenses retain a 5% residual tint even in the dark which may interfere with visibility in dark. Photo chromatic lenses are available in glass and plastic. The photo chromatic effect is achieved by the addition of silver halide crystals to the lens material which change color only when exposed to UV light. Therefore, they are ineffective while you are driving a car as the wind-screen itself will absorb the UV rays and there will be no photochromic action. Photo chromatic lenses are generally referred to as "sunglasses" by the layman and not an ideal substitute for dark glasses to beat the tropical summer. But when the temperatures shoot over 43 deg C, the efficiency of these lenses wares off.

Sunglasses
Sunglasses, glares, dark glasses call them by any name, the basic function remains: the same protection against the visible and invisible sunlight. Sunglasses are fast becoming a more visible fashion accessory these days, although in a tropical country like India, they are very much a necessity. Sunglasses not only serve as shields from the harmful effects of the visible (glare and dazzle) and invisible (Ultra-violet and Infra-red) rays of the sun, they also protect the eyes from wind and dust. (LINKS : Lens Colors, Photochromic Lenses, Polarizing Lenses, Tips, UV Protection) LENS COLOR The lens color is an area where you can experiment with the palette. With the plastic lenses now possible in any tint and power, the choice is wide open. Lighter colors as fashion tints serve the dual purpose of braving moderate amounts of sun and acting as a shield to the eyes from the wind and dust at night. However, keeping the Ahmedabadi summer in mind the best would be the dark gray and green colors. In glass, the colors that usually help beat the heat are the dark green (Calobar ), Dark Grey and Dark Brown.