Artificial lenses have a very long history of being used in the eye. In fact, artificial lenses were invented over 70 years ago! Those lenses were good, but since then decades of progress has further refined the cataract lenses we use today.
Artificial cataract lenses are well tested and designed to last forever. This is due to the the unique non-reactive material and the location that these lenses sit within the eye. Very rarely does the artificial lens need to be removed or replaced.
But before taking a look at the modern artificial cataract lens, let's rewind the clock to see what led to the discovery that lenses can actually work after cataract surgery.
Background On The Discovery Of Artificial Cataract Lenses
Cataract surgery was revolutionized by the invention of the artificial cataract lens. What we take for granted of being able to see great without glasses after cataract surgery wasn't always the case.
You see, when we use our eyes, light must focus on our retina in the back of the eye. Both the cornea and the natural lens inside our eye do all this focusing (with a pair of glasses making up any additional focusing needed). The natural lens, which does about one third of the job later goes on to become cloudy and become a cataract. And this cataract is removed with cataract surgery.
Without artificial lenses, the focusing power of this cataract must be replaced with glasses. And this led to very very large prescriptions of glasses (prescriptions so large that they frequently caused extra distortions in vision).
And this was the way cataract surgery was performed. Once the cataract was removed, large thick glasses were given to improve the vision.
But a savvy ophthalmologist noticed something during World War II. Sir Harold Ridley worked in Great Britain taking care of pilots that were shot down during the war. In some of these injuries, glass and plastic from the cockpit got inside the eyes of these pilots. Doctor Ridley noticed that these materials didn't cause any reaction inside the eye.
So after the war, Ridley started to experiment with the plastic used in the airplanes - acrylic or PMMA (also known by the trade name Plexiglas). He molded this plastic into a lens and implanted it within the eye after cataract surgery.
And 70 years later, this same type of plastic is still used for the artificial cataract lenses today.
Modern artificial lens used in cataract surgery; image by Frank C. Müller, CC BY-SA 3.0, via Wikimedia Commons
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Why Cataract Lenses Last Forever
That brilliant observation by Sir Harold Ridley identified a wonderful non-reactive material to manufacture cataract lenses. And to this date, there have been no allergies to artificial cataract lenses. The body doesn't react to the lens. Since then, other materials, such as silicone have also been identified as non-reactive and been used for cataract lenses.
But the material is only one part of the equation. This lens is also set up for success by the way cataract surgery is performed.
If the new artificial cataract lens rubbed against different parts of the eye, it would aggravate those structures. This occurred more commonly in the past with different lenses and cataract surgery techniques leading to an increase in inflammation within the eye.
So to prevent the artificial cataract lens from rubbing against other structures, it is placed within its own compartment.
This compartment already exists within the eye; turns out this is the compartment that the cataract sits in - called the capsule bag.
Capsule within eye; image by File:Three Internal chambers of the Eye.png: Artwork by Holly Fischer derivative work: Pixelsquid, CC BY 3.0, via Wikimedia Commons / modified from original
During cataract surgery, when the cataract is removed, this capsule bag is left behind. The new artificial lens is placed inside this capsule bag which suspends and secures the lens within the eye and away from any other structures of the eye.
So what we have left is a non-reactive plastic in the eye within its own separated compartment. This is the reason why these artificial cataract lenses last forever.
When Might They NOT Last Forever
Of course there are always exceptions in life. And yes, there are times in which these artificial lenses may need to be replaced. Fortunately, these situations are pretty rare.
Dislocation of the lens
The biggest reason why an artificial lens may need to be replaced is if it moves out of the correct position.
That capsule bag (which now contains the artificial lens) is suspended in position with tiny fibers called zonules or suspensory ligaments. When all those zonules are strong, the lens remains perfectly suspended and centered within the eye. If those zonules become weak, there may not be enough support to keep the lens centered and the lens can dislocate out of position.
This can mean a surgery to replace or recenter the lens.
Fortunately this is rare. The risk of this happening up to twenty years out from cataract surgery is less than 1%. But certain medical conditions can increase the risk of this happening.
Learn more at Key Symptoms Of Dislocated Lens After Cataract Surgery
Lens gets cloudy
Throughout the history of artificial cataract lenses, there have been certain lenses that have become more cloudy over time.
Some of these lenses have developed calcifications that required the lens to be removed. (Fortunately, none of these lenses were ones commonly used in the United States).
Of the more common lenses, the Acrysof line of lenses by Alcon had a propensity to develop haziness over time. While this particular haziness didn't significantly affect vision, it has since been replaced with a model designed to solve that haziness issue.
This leaves us today with artificial cataract lenses that are expected to remain clear forever.
Note on silicone lenses: Certain complex retinal surgeries involve the use of silicone. This silicone can deposit on the back of silicone lenses and cloud vision. Because of this, silicone cataract lenses are often avoided if there is any future risk of needing a retinal surgery.
What CAN Make Vision Blurry
Despite cataract surgery lasting forever and despite the artificial lens also lasting forever, this doesn't mean that vision will always be perfect. There can be other reasons why the vision becomes blurry after cataract surgery.
What's the biggest reason? Well, it's actually that capsule bag!
When the cataract is removed, some microscopic cells of it can remain behind. Don't worry, these microscopic cells aren’t going to regrow the cataract. But these cataract cells can attach to the back of the capsule and start growing. As these cells start to grow on the back of capsule, they make it cloudy. And this cloudiness starts to blur vision.
Having a cloudy capsule (medically known as posterior capsular opacification or more colloquially as “after-cataract") is pretty common after cataract surgery. But fortunately it is very easily treated with an in-office laser procedure.
For further information, check out The BIGGEST Reason for Blurred Vision 2 Years After Cataract Surgery
Summary
The cataract lenses used during cataract surgery are designed to last forever. This is due to the unique non-reactive material that the lenses are made from as well as the unique position that these lenses sit within the eye.
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