Chapter 2: Implants and Measurements
During cataract surgery, we place an implant inside your eye. This implant is crystal clear and gives you crisp vision. These implants also come in different prescriptions and can drastically reduce your dependence on glasses after surgery. But, before we get into details, let’s start with the basics.
What exactly is an implant?
The “implant” is the plastic lens that we place inside your eye. When we remove your cataract, a new lens has to go back inside to replace it. Without a new lens, you wouldn’t be able to see. Before lens implants were invented, people had to use coke-bottle glasses after cataract surgery to get around.
The modern implants we use are made of a flexible acrylic plastic. These plastic lenses are inert, don’t cause inflammation, and do not “go bad.” They have been in use for decades and have a proven track record. Because the implanted lenses are flexible, they fold up very small and can be injected into the eye through a very small incision. Once inside the eye, they unfold like a flower and don’t move. You cannot feel the lens in your eye … your eye will feel normal afterwards.
How will the new implant affect my vision?
The new implant in your eye is optically clear. It should make your vision clearer and reduce glare that was caused by your prior cataract.
How will the new implant affect my eyeglass prescription?
One of the neat things about cataract surgery is that we can change the overall prescription of your eye. The new implant comes in different prescriptions, just like glasses or contact lenses. The power of the implant will determine if you are nearsighted or farsighted.
Most people prefer to have clear distance vision, and choose an implant that will allow them to see far-away objects like the television or road signs. If you have extremely thick glasses now, you’ll be pleased to learn that after your cataract surgery you’ll be less dependent upon them. You may be able to see at distance without any glasses at all! We will be measuring your eyes before surgery to pick the correct implant prescription power for you.
Why do I need my eyes “measured?”
We need to measure your eyes ahead of time to pick the correct lens implant to put into your eye. When we perform cataract surgery, we remove the cataract from your eye … but it has to be replaced with a new lens in order for you to see afterwards. The new plastic implant is a magnifying glass, and just like glasses or contact lenses, the implant comes in different prescriptions.
Now, it’s pretty easy to measure you for eyeglasses. We use an eye chart in the office and can spend all day holding up different lenses in front of you, tweaking your vision to perfection.
We can’t do this trial-and-error approach in the middle of your surgery. We can’t tape an eye chart on the operating room ceiling and swap implants in and out of your eye … all the time asking you “what’s clearer … one or two?” It’s just not feasible! Instead, we calculate what lens you’ll need AHEAD of time.
How do you calculate my implant power?
We calculate the power of your new implant using two measurements: the length of your eye and the steepness of your cornea. We take these measurements, and using special mathematical formulas, determine the correct implant lens for you.
In other words, we compare YOUR eye measurements to the eye measurements of ten thousand OTHER PEOPLE with similar eyes and say to ourselves:
“The implant power that gave the majority of THOSE people good vision will, hopefully, be the same implant power that gives YOU good distance vision as well!”
This tends to work well on average. However, your eyes might not be “average.” As individuals, we have unique ocular anatomy. Sometimes, people end up a little more near- or farsighted than we predicted. This is correctable with glasses/contacts, but some people are a little disappointed that they still require glasses for best vision.
Fortunately, most people end up with good vision and are able to see well at distance with little or no glasses required. You might still need eyeglasses for “perfect” (20/20) vision, however.
I wear contact lenses now … is this going to affect my measurements?
You should stop wearing your contacts a few weeks before we measure your eyes. Contact lenses can distort our measurements and make our implant calculation inaccurate. This is especially true with hard contact lenses. Let us know if you wear contacts.
I’ve had LASIK in the past. Is this going to affect my cataract surgery?
Prior LASIK will not affect your surgery, but will make it harder to predict your eyeglass prescription afterwards.
When you had LASIK, the corneal surface of your eye was reshaped with a laser. The implant calculations we use can’t take into account your prior operations unless we know what your prior refractive error was. We don’t know how much laser energy was used. We don’t know the size of the treatment zone ablated. These unknowns make it more challenging to pick the “correct” implant power to put back into your eye.
It can be helpful to obtain your LASIK records to see what your prior measurements were, and our surgical coordinator will help with this. Unfortunately, many people had their LASIK years ago by another doctor. If your laser surgery was more than seven years ago, these records may no longer exist! Many paper-based charts are incinerated after seven years to save space!
Don’t worry, we can still calculate your lens implant power and you’ll likely have good distance vision after surgery. However, the “unpredictability” is a little bit higher and there is an even greater chance that you’ll need some glasses for crisp distance vision. This is important for you to know, as most people who had LASIK are motivated to be “eyeglass free.” We want you to be prepared and not angry if you end up in glasses again.
If my prescription is off, can you swap out my implant?
There is risk with surgery, and we want to avoid another operation. However, if your prescription ends up WAY different then expected, and LASIK correction doesn’t appeal to you, then a lens exchange may sometimes be an option.
But wait … isn’t the goal of cataract surgery to get me out of glasses?
The goal of cataract surgery is to reduce glare and make your vision crisper, NOT to get you out of glasses. While it is wonderful if you end up less reliant on glasses … this is a benefit, and not the main reason for this operation.
After surgery, many people have good enough distance vision to drive without glasses … but perfect 20/20 distance vision is not always possible without a little help from spectacles. Also, you will definitely need some kind of reading glass or bifocal.
There are some new “premium implants” on the market which may make your end-prescription MORE predictable, but even with these new implants there is no guarantee you’ll be without some kind of correction. We’ll discuss these premium implants in the next chapter.
Why would LASIK give a more predictable prescription than cataract surgery?
With LASIK, a laser beam is used to reshape the surface of the cornea on the OUTSIDE of the eye to change your prescription. This outer ocular surface is easier to measure and manipulate with a laser beam and the end refractive results are quite predictable.
With cataract surgery, however, we are replacing the lens INSIDE the eye. The interior anatomy of the eye is different for everyone. It is impossible to predict 100 percent what prescription (if any) you’ll need after this type of surgery.
Can you just give me monovision so I won’t need reading glasses?
Monovision is when one eye is set for distance, while the other is set for near. Many contact lens wearers use a “monovision contact prescription” to avoid reading glasses. Most will set their dominant eye for distance and their non-dominant eye set for reading.
While some people tolerate this imbalance well, other people hate monovision. The disparity between their eyes makes them sick to their stomach and unsteady on their feet. The blur at distance ruins their depth perception for driving, and reading becomes a chore because one eye is doing all the work.
Imagine if we set your eyes permanently this way during your surgery. If you don’t like your monovision, it’s going to be hard to change those implants! At least with glasses or contacts we can take them off or pop them out.
If you’ve been using monovision contacts for years without issue (or your eyes are “naturally” focused this way), then we may purposefully shoot for monovision after discussing this during your clinic visit.
In the end, most people prefer to have both eyes in synch with each other. You can always put a contact in one eye for monovision afterwards if you really want it.
Can you purposefully make me nearsighted so I can read without glasses?
Most people prefer to have good distance vision and cataract surgery is an opportunity to set your eye’s focus for that. However, some nearsighted people are able to read without any glasses at all.
These people read all day long and can’t tolerate reading glasses at all … but don’t seem to mind glasses for watching television or driving!
If you are one of these nearsighted creatures, we can purposefully leave you nearsighted to maintain your current focus. It’s important you tell us about your post-operative “visual goals” to help make this decision.
I only have a cataract in one of my eyes. How might this affect my prescription goals?
When choosing your implant, we have to keep your ocular balance in mind. We don’t want to make your eyes too “different” from each other or you will be uncomfortable afterwards. If we make you nearsighted in one eye while your non-operated eye remains farsighted, your glasses will end up lopsided and the resulting image disparity will give you eye-strain and headaches. Your brain won’t like it!
In these cases, we may purposefully under-correct you to give you better “balance.” You’ll still be in glasses, but at least you’ll be comfortable. We will, of course, discuss this with you prior to surgery.
