Question: What is a cataract and how does it develop?

Michael Kelly answered on 25 Jun 2014:

The lens is made of transparent proteins called crystallins, they are very tightly packed inside a capsule and when you are young the whole structure is elastic and can be deformed. This is how you focus on objects that are near to you.
As you get older the proteins are continually produced and become more compacted, they also become yellower. This gives rise to a brown or brunescent cataract and this makes blue lights harder to see.
There are three other types of age related cataract. The first, called nuclear cataract occurs when the centre of the lens becomes very dense. The lens stays clear but there is a rapid change in the glasses prescription, usually in the direction of short sightedness. A second type is when water enters the lens, this disrupts the regular structure and the lens looks like it has spokes, this called a cortical cataract, because it is in the cortex of the lens. The lens is still clear but the focusing of the light is the same as if it was passing through a broken glass. The final age related type is called sub-capsular, there is a build up of material on the back surface of the lens capsule, right in the middle, this can be a problem when reading or driving at night because it scatters the incoming light producing glare. Often these four age related cataracts occur together. There are also cataracts due to injury, altered metabolism, inherited disorders and medicines.