In the same way that a usual cataract develops, a complicated cataract also occurs when the lens at the front of the eye starts to become cloudy.

This prevents the retina from receiving light rays in the way they should, causing vision to become impaired.

These will eventually need to be treated, as the condition will only continue to progress over time, and vision will continue to deteriorate. With the complicated cataract, the progression can be more rapid and dramatic, as the posterior central part of the lens is affected. Unlike a cataract that forms as a result of ageing (senile cataract), complex cataracts can be just as common in children as they are in adults.