Cataract surgery is a very safe procedure with generally very high patient satisfaction rate. Even so, no surgery is ever risk free. Complications which can adversely affect the visual outcome can occur during surgery or post-operatively.
Whilst the list of specific causes for these complications is long, the overall incidence is a small fraction of cases. The most serious complications during surgery are a tear of the thin capsule at the back of the lens (posterior capsule rupture) or spontaneous haemorrhage from the thin vessels in the deeper layer of the retina. The most serious post-operative complications are retinal detachment, which is more common in very short-sighted eyes or younger patients (under 50s), infection (1-2/1000). Overall there is a reported 1 in 1000 chance of loss of vision and 1 in 10000 chance of losing the eye.