I have heard the term 'Cataract' since ages. I never bothered to understand what exactly it is. I have heard of elders being troubled by cataract. It is only recently that I understood what it does to the way you see things around you, and how vision changes as a result of cataract, which occurs as a result of ageing.
In short, the vision gets blurred, and a few filters are applied to the colours you see, hence making them appear different than what they really are. Usually the cool colours - greens, blues, purples - reduce and are instead replaced by a bunch of warm colours - reds, oranges, yellows. Hazier vision, blurry lines and less detailing.
One of my all time favourite artists - Claude Monet - suffered from cataract. And his entire style was based on the play of light on objects and the plethora of shades of colours that occur at various times of the day. There were no lines, there were only illusions or impressions of an outline, created by colours. He had recurring motifs that were studied across different points of time.
Here is one such recurring motif painted before the onset of cataract, and after the onset of cataract!
Source: www.intermonet.com