Come summers and people start using shades for their eyes, also called sun glasses.

It is a necessity, actually!

1) They cut down intensity of light entering the eye, thus reducing 'glare'

2) They absorb UltraViolet light that causes early cataract formation and also damages eyelid skin

3) They provide additional barrier to dust and hot winds

It is a fashion statement as well!

1) They are available in different shapes and sizes

2) They are available in different colours

3) They are a power statement for some 

Ensure the following while buying Shades:

1) The frame should rest comfortably on the nose and should not be tight as it can cause skin irritation and excessive sweating.

2) It should cover the eyes completely and may be curve around the edges to give greater protection

3)The lenses should absorb both the UV spectra- UV A and UV B.  Certificate to this effect should be there with the shades. 90% absorption should be assured

4) There should not be any distortion in vision

5) Grey and blue shades reduce more glare than other shades.  Coloured shades change your colour perception till the time you wear them. Grey and blue are safer bet for this reason.

6) Polarised lenses cut glare more effectively.

7) Prescription shades are also available be careful as the darkness varies with lens thickness. 

Sunglasses are a useful accessory that play a specific role in reducing glare and evaporative tear loss. They also help in absorbing harmful UV radiation that can affect eyelids and lead to an early cataract.