Contrast in vision is the ability to distinguish between an object and its background or to tell the difference between similar shades of light and dark.
Contrast sensitivity is now considered as important as visual acuity (visual acuity being how sharp your vision is at a given distance).
Contrast allows us to better see in different conditions such as at dusk, foggy or rainy days, in the presence of reflective glare, and while driving at night.
Contrast also effects depth perception which is the ability to judge the distance between two objects and to see in 3D (including length, width and depth).
A decrease in contrast can lead to the loss of spatial awareness, mobility and can increase the risk of accidents.
Quality polarized lenses are excellent for enhancing contrast, particularly in the presence of reflective blinding glare such as that created by wet roads, reflected light from water, snow and fog.
It should be noted that polarized lenses should not be worn at night.