The cornea (the clear window at the front of the eye) would be completely spherical in an ideal world however the great majority of people have some degree of astigmatism where the cornea is more rugby ball shaped. If you imagine a magnifying glass which is rugby ball shaped you will appreciate that it would be hard to focus the light properly and get a clear image. This astigmatism of the cornea causes blur and is corrected by spectacles. This astigmatism has an effect on vision on top of any long or short sightedness you may have.
When we undertake ordinary cataract surgery we work out what power of lens to put into the eye to try and take away any long or short sightedness but if you are left with astigmatism that will mean that your unaided vision (vision without spectacles on) can still be sub-optimal.
Because astigmatism involves the cornea being more curved in one axis than the other (rugby ball shape), incisions can be used in the more curved axis to reduce the astigmatism so the cornea has a rounder shape (football). This can be unpredictable and the results variable. A more elegant solution is to implant a lens that takes away the astigmatism from inside the eye.
Toric IOLs designed to correct astigmatism of varying degrees and are placed after routine cataract surgery. They are ordered in especially after numerous scans and calculations.
Risks include poor vision due to the lens rotating out of position, with the possibility of further surgery to reposition or replace the IOL.
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