A cataract occurs due to clouding or dysfunction of the natural crystalline lens of the eye. When cataract surgery is performed, this natural lens of the eye is removed and replaced with a man-made lens implant to restore focusing of incoming light.
Before the age of about 40, your natural lens has a kind of "autofocus" mechanism that allows you to enjoy a range of focus from distance to near. This is due to tiny muscles in the eye that pull on the lens to change its shape and focus.
As we age, the natural lens hardens and responds less and less well to these focusing muscles. The result is a condition called "presbyopia." By the time we reach 60, we have almost no ability to change the focus of our lens.
Traditional cataract surgery replaces this lens with a "basic" monofocal implant lens. Monofocal means the implant focuses clearly at only one distance. If the implant focuses well at "distance" it will reduce or eliminate the need for distance glasses - it is like putting the top part of a bifocal glasses "into" the eye. The power or strength of the implant is calculated by taking measurements and using various formulas. These formulas are reasonably accurate, but some patients may still need glasses at times for distance vision after surgery.
When the implant power is chosen correctly, and there is no significant astigmatism, distance vision is usually excellent without glasses. Most people will still need to use reading glasses, however, because the autofocus mechanism works poorly with traditional implants.
There are now various implants which perform better than basic implants. They are sometimes called "premium" implants. These have the added advantage of either correcting for astigmatism, or improving focusing range, or both.
Astigmatism is a condition where the light entering the eye does not come to a single sharp focal point. Instead, the light focuses as a "smear" across a region of the eye. The result is blurred vision. Implants that correct astigmatism can help sharpen vision at distance when astigmatism is present by neutralizing the astigmatism.
Astigmatism is usually due to a cornea that is ovalled like the side of a football, rather than round like a baseball. It can also be caused by abnormalities in the lens of the eye.
Implants that improve range of focus can improve the odds that glasses will be needed less for intermediate, reading, or close tasks. Some, but not all patients may be able to function well without any glasses.
Implants that correct for both astigmatism and improve focusing range can help to accomplish both goals.
The choice of an implant is based on several factors. These include visual potential, visual goals, characteristics of your eye, the implant, and cost. Premium implants incur extra charges that may include part of the cost of the implant as well as refractive services (since they are used to reduce the need for glasses over and above merely replacing the cataractous lens). These extra charges vary with the implant used and are never insurance covered.
The choice of implant lens is made after discussing the goals and costs of surgery with the patient.
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