Summer in coming, UV protection frequently asked questions

What are ultraviolet rays?
Ultraviolet (UV) rays are part of electro-magnetic radiation. They are invisible rays lying beyond the violet end of the visible spectrum. 
Low intensity of UV rays are also emitted from fluorescent lamps, TV and computer monitors. 
Are there different types of UV rays?
As different intensity (wavelength) of UV has different effect on us, they are commonly categorized as UV-A, UV-B and UV-C. 
UV-C (wavelengths from 200nm - 290nm) is present above the earth's atmosphere and also given out from welding arcs. It also arises from sunlight's reflection from snow at high altitude. 
UV-B (wavelengths from 290nm - 320nm) and UV-A (wavelengths from 320nm - 390nm) are present in our living environment, from direct sunlight or reflection from snow, water, sands, glass windows, concrete walls etc. 
What are the harmful effects of UV rays on human eyes?
The effects and damages to the eyes from the UV radiation are well documented. 
Since various ocular tissue layers absorb different wavelengths of the UV rays, they can respond quite differently. 
The cornea is particularly susceptible to the effects of UV-C and lesser extent of UV-B. UV-C given off by a welding arc can be absorbed by the cornea and symptoms of foreign body sensation, tearing and pain may appear between 30 minutes to 12 hours after exposure. Excessive exposure has been documented to cause corneal cells damage. 
Corneal absorption of UV radiation decreases dramatically at wavelengths above 290nm. 
The portion UV-A and lesser extent of UV-B are transmitted through the cornea and aqueous, and nearly totally absorbed by the crystalline lens. Although painless, it can alter the lens nuclear proteins and lead to lens opacification (cataract). 
UV of long wavelengths transmitted through the lens will be received by the retina as have been implicated in macula degeneration and damaging retinal tissues. 
Pterygiums and Pingueculae have also been known closely associated to the exposure of UV rays. 
Besides sunglasses, is there any UV-block lens for spectacle wearers?
Normal human activities can not avoid exposure of eyes to the UV radiation. Although domestic fluorescent lamps, TV and monitors emit very small amount of UV radiation, it's prudent to protect the eyes from the cumulative effects of UV on long term exposure. 
They are various lens types, such as Hi-index, Photochromic (Transitions), Polycarbonate lenses, which provide up to 99% of UV block without having the dark tint as with the sunglasses, allowing all day wear out and indoors.