Cataract Surgery Options for Distance, Intermediate and Near Vision
There are many options to consider once you’ve made the decision to have your cataract removed. Cataract is the name given to the natural lens of the eye when it becomes cloudy or opaque. The natural lens is the main focusing element of the eye. If it is removed without replacing it with another lens, the vision would be very poor. That is why cataract surgery involves both the removal of the cataract and the placement of an intraocular lens (IOL).
The natural lens of the eye can change shape when we are younger, allowing us to focus on near objects when accommodating and to see in the distance when the eye is relaxed. Over time and with age, the eye and lens slowly loses it’s ability to focus on near objects. This process is called presbyopia, and explains why many people require reading glasses as they reach their early to mid forties. When a cataract is removed and an IOL is placed, the eye will not have the same ability to accommodate to see near objects, as the IOLs do not change shape like the natural lens does.
It is important to understand that there are choices available when it comes to deciding which IOL to place. There are monofocal IOLS, which have one focal point, and there are multifocal IOLs which have been designed to have two or three focal points. Multifocal lenses are designed to have different areas of the lens with different focal points to allow you to see in the distance as well as near. However, there are important limitations in their ability to understand before deciding on a multifocal lens. The easiest way to describe this limitation is with an example. If you consider all of the light entering the eye to be 100% of the light, then an multifocal lens may focus 50% of that light at distance and 50% of light at near. That means that it is not possible for 100% of the light to be focused all at distance or all at near, as there is always some fraction of the total focused at both distances. Patients are more likely to complain after having a multifocal lens placed that their distance vision and near vision is not as clear as they had hoped. However, the major benefit of these lenses are that they do provide the ability to see both distance and near without the near for reading glasses. It is particularly important to understand this if there is some other reason for the vision to be compromised, as placing a multifocal lens could lead to further reduced vision.
Monofocal lenses by definition are focused at one distance. It is possible to have both distance and near vision after cataract surgery using a different target focal length for each eye. Most often patients are happier with a distance focal length IOL placed in their dominant eye and a near or intermediate focal length IOL placed in the non-dominant eye. This is termed monovision. An important point to understand is that about 20% of the population will not be able to tolerate monovision, and may double vision after both a distance and near IOL are placed. It is always best to check this prior to surgery.
Please do not hesitate to discuss any of the above issues with me at the time of your preoperative clinic appointment.