What type of intraocular lens (IOL) should I choose?
Cataract surgery involves the removal of your cloudy lens and replacing it with the insertion of an intraocular lens (IOLs). Various IOLs are available:
Standard IOL (monofocal)
This IOL does not correct for astigmatism and is designed to deliver good vision at only one distance (usually for distance). You will still need glasses for computer work and for reading. If you have astigmatism, you will need glasses after the surgery for both distance and for reading.
Designed to reduce your need for eyeglasses for both distance and near vision. There is an option for multifocal toric IOL if you have astigmatism.
Designed to treat astigmatism and deliver excellent vision at a single distance. You will still need glasses for computer work and for reading.
What is Astigmatism?
In an eye with astigmatism, the shape of the cornea causes light to fall on multiple points, either in front of the retina or behind it (or both). Astigmatism usually causes vision to be blurred or distorted to some degree at all distances.
Toric IOLs help to reduce the amount of residual astigmatism and reduce your dependence on wearing glasses. They do not totally negate the amount of residual astigmatism.
Before the day of surgery, additional measurements and calculations are taken to allow the doctor to choose the correct toric IOL power and the required alignment of the implant in the eye to correct the astigmatism accurately.
Toric IOLs have special markers that enable the surgeon to rotate the IOL in the eye so the astigmatism correction is properly aligned. Use of a toric IOL during cataract surgery does not increase the risk of common cataract surgery complications. Occasionally, the intraocular lens implant may move post-operatively causing it to become off-alignment. This can result in residual astigmatism. A second surgery can be done to realign the IOL. The alternative to the second surgery may be to wear glasses to correct the induced astigmatism instead.
Multifocal IOLs are designed to allow you to see clearly at more than one focus point. This allows spectacle independence most of the time and is more convenient.
However, side effects of all multifocal IOLs include decreased contrast sensitivity, characteristically experienced as a loss of some clarity in dim lighting. Patients may also experience some glare and haloes especially at night (headlight of oncoming vehicles). It may still be necessary to wear glasses to read especially in low light conditions and when the wording is very small.
Limitations related to Toric and Multifocal IOLs
In situations where the lens bag is unstable or broken, the surgeon may decide that it is not suitable to insert a toric or a multifocal IOL because the IOL will not be able to sit centrally in the capsular bag. The surgeon may decide to insert a monofocal non-toric lens in the capsular bag instead.
Despite advances in IOL power calculation, there is a small risk that there may still be residual refractive error post cataract surgery. It may then be necessary to correct that with refractive surgery or the patient may choose to wear glasses.