If the most of UV light is absorbed by glass, does a person wearing prescription eye glasses need to wear sun glasses? A person on the in side of window dose not get sunburn because most of the UV rays do not pass through glasses, then would the same property be true for glasses?  could plane prescription glasses protect eyes from harmful UV rays?  Why do sun glasses need UV protection coating?
 A: Eyewear is not usually made of glass these days.  Some plastic lenses block all UV, but some plastics allow some UV to pass so a coating is used.
For glass.. see this article about car window glass. Not all UV is blocked without a UV treatment.
http://www.skincancer.org/prevention/are-you-at-risk/sun-hazards-in-your-car
A: Optical materials such as glass and plastic do not lower the level of UV low enough to be safe for the eye without very specific design for this function. So normal eyeglasses will not shield the eye from UV damage. 
The level of UV that is harmful to the eyes is considerably less than the level which can effect sunburn. Moreover, the wavelengths that cause sunburn and eye damage are different; the former tend to be longer wavelengths, the latter shorter and more energetic. Chronic exposure to even low levels of UV seriously increase the risk of eye damage, including retinal cancers. Eye damage happens primarily through phototoxicity, i.e. chemical changes induced by energetic light.
So the protection against sunburn and against UV eye damage are quite different problems. Even if light through a window does not cause sunburn, it can still effect  other, photochemical damage to living skin layers and raise the risk of melanoma.
