Types of cataract
Not all cataracts are the same. There are three common types of cataract, each of which looks different on examination and produces different effects on your vision. Some people have a mixture of more than one type of cataract.
Cataracts are sometimes described as “growing”. This does not mean that there is a “bigger” lens to remove, just that more of the lens is affected, or sometimes that the cloudiness is more marked.
Nuclear cataract is the commonest form of cataract. This type of cataract tends to blur and dim vision; it particularly causes a dimming of blue colours (so things tend to look blue and fresh following its removal). Nuclear cataract often causes the focus of the eye to change so that it becomes more myopic or less hyperopic or sometimes develops astigmatism.
Cortical cataract affects the outer parts of the lens first, away from the central part we look through. As it progresses, spokes of cloudiness spread centrally, affecting sight. Often the vision on an eye chart will seem quite good, but real-world vision will be much worse, with glare and a loss of contrast. Vision is particularly poor when there is oncoming light; car headlights or low sun are particularly troublesome and this type of cataract may make driving difficult or even dangerous.
Posterior subcapsular cataract is a type of cataract that affects the very back of lens, just inside the lens capsule. The lens capsule is the thin skin of the lens, a bit like the skin of a grape. This type of cataract can be present for many years before causing symptoms, but once the sight is affected it can progress rapidly, sometimes taking just a few months to go from onset of symptoms to marked loss of sight. Drugs such as steroids can cause posterior subcapsular cataract.