Check the lens of the sunglasses for its quality and make sure it is zero-powered.
When you look through it,the image that you see on the other side of the lens should not move or change like a blur when you move the glasses up and down or sideways, says Dr Mahipal Sachdev,Opthalmologist,Centre for Sight,Delhi.
Glass or plastic?
There is no difference between glass or plastic lenses,both work fine, says Dr Sachdev. For children,it is advisable to wear plastic glasses for easy handling. Also,look at the lens closely for impurities and scratches.
UV filters,a must
The right pair of sunglasses will give your corneas protection from the suns ultraviolet rays.
Scientific research has clearly linked cataract,macular degeneration,snow-blindness,pterygium and skin cancer to the corneas and retinas over-exposure to ultraviolet rays. There can be an onset of early cataract and macular degeneration if the eyes are not protected. Buy branded glasses to be sure of the UV protection.
Fitting and cleaning
Your sunglasses should sit comfortably on the nose bridge. Keep the lens clean,an oily coat causes diffraction of light and may strain the eyes.
Grey,brown or dark green shades are suited for blocking light,other colours like blue,purple and pink are just fashion statements. It is also not good to have a gradation (light to dark) in sunglasses.
Mirror finish glasses
An anti-reflective coating helps throw light away. When you are in high contrast conditions (sunny afternoons or at the beach),it makes sense to use anti-reflective glasses. They dont work well in poor contrast conditions.
Places where sunglasses are a must
Hills,especially if snow-covered,reflect light. Higher altitudes (aviation) and looking at the sea (water bodies reflect light) call for the use of sunglasses. Also in traffic,one must use sunglasses,as here,they not just fend off UV rays but also act protect against pollutants.