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Your Complete Guide Of Lenses For Cataract Surgery
Cataract surgery is amazing not only in that we remove a cataract and improve vision with glasses, but we also have the ability in many cases to get out of glasses after cataract surgery. This is due to special artificial lenses placed in the eye following the procedure.
These lenses after cataract surgery fall into a few different categories.
The standard cataract lens is called a monofocal lens and will require glasses after cataract surgery. A step up from that are toric lenses which correct astigmatism. But then we move into more advanced lenses such as light adjustable lenses, accommodating lenses, multifocal lenses and extended depth of focus lenses that can significantly improve vision without glasses.
Lots of cool technologies to talk about!
I know you are just itching to get in and start learning about all the different lenses there are for cataract surgery, but first we have to go over some important background information. The main reason so many different types of lens exist is to improve upon the way vision can be corrected after cataract surgery without glasses. So having some understanding of how prescription in the eye works will be helpful to understand what you can expect to see with the different lenses.
Your Prescription Changes After Cataract Surgery
That lens inside your eye that became a cataract? Well, that lens took part in your eye prescription.
About two-thirds of light that enters the eye is focused by the front clear part of the eye called the cornea. The rest is focused by the lens. Where the cornea and the lens focus this light determines your prescription (if everything focuses perfectly on the retina, then you have perfect vision - no prescription).
Light focusing in the eye; image by Sunshineconnelly at en.wikibooks, CC BY 3.0, via Wikimedia Commons
If this light focuses in front of the retina, you are shortsighted or nearsighted; if this light focuses behind the retina, you are longsighted or farsighted. (see also What's The Difference Between Short Sighted vs Long Sighted?)
When we remove the cataract, we replace it with a new artificial lens. This lens has focusing power similar to how the cataract / lens had focusing power.
But the focusing power of this new lens does NOT have to match what your old lens used to be. Instead of being nearsighted or farsighted, the power of this lens can be chosen to focus light perfectly on the retina instead. Giving you perfect distance vision without glasses.*
*Unless you have astigmatism - returning to that in a bit.
This new artificial lens is inflexible
Notice how I said perfect distance vision. This new lens is incapable of changing focus. In fact, if are in your late 50s or older, your cataract was also incapable of changing focus.
But younger than that, the lens can actually change shape and change focus. Before your 40s, the lens is flexible and able to change focus to avoid the need for reading glasses or progressive glasses. But through something called presbyopia, the lens becomes inflexible and reading glasses become necessary.
It’s the same thing with the artificial lens. A standard cataract lens can only focus where the power of the lens allows it to focus - which is typically calculated for the distance. Up close will be blurry and require reading glasses. (See also The Reason For Loss Of Near Vision After Cataract Surgery)
This is one main reason why there are so many different types of cataract lenses. To try and extend the focus beyond just the distance.
Now that we’ve got some background behind us, let’s dig into the artificial lenses.
Standard Monofocal Lenses
These are the most common variety of artificial lenses used during cataract surgery. These types of lenses have been used for decades.
These particular lenses may also be referred to as basic lenses or single focus lenses. These are the lenses covered by insurance plans for cataract surgery.
The key distinguishing feature is that these lenses can ONLY focus in one direction. (Pretty much what I described in the last section). In addition, these lenses CAN’T correct any astigmatism.
For the most part, with monofocal lenses, you will need glasses afterwards. With your vision corrected for the distance, you will need reading glasses. (See also How To Pick The Best Reading Glasses After Cataract Surgery). And depending on the amount of astigmatism you have, you may require glasses (or bifocals or progressive glasses) for distance vision.
In the United States, there are 3 major artificial lens manufacturers; and they all of course make a monofocal lens. And as you’ll see, each artificial lens has its own name.
Ok, so far I’ve mentioned that artificial lens don’t correct astigmatism. But that only applies to the standard monofocal lens. Every lens coming up, including the next one, the toric lens, can correct astigmatism.
But it is worth noting that the astigmatism you have before cataract surgery doesn’t necessarily equal the astigmatism you have after cataract surgery.
Astigmatism in your vision and glasses prescription mostly comes from your cornea (the front clear part of your eye), but some can also come from the lens inside your eye. - the one that is removed during cataract surgery. Because this lens is removed during cataract surgery, astigmatism afterwards is largely due to the cornea and the astigmatism correction during cataract surgery is based upon the cornea measurements. For some people, this may mean a need for astigmatism correction during cataract surgery despite not having much astigmatism in their current glasses prescription. In fact, a third or more of all patients will have a significant amount of astigmatism after cataract surgery unless corrected!
These lenses are very similar to the standard lenses except for one key difference - these lenses can correct astigmatism. And these lenses can correct quite a bit of astigmatism as well, all the way up to 6.00 diopters of astigmatism power!
Toric cataract lens; image © 2018 Jung, N.Y., Lim, D.H., Hwang, S.S. et al., used under CC BY 4.0 / modified from original
Notice the dots on that particular lens? After the lens is placed within the eye, this lens is rotated until those dots line up with the direction of the astigmatism in the eye. This is how a toric lens corrects astigmatism.
By eliminating astigmatism during cataract surgery, we open up the door to getting out of glasses. Similar to the monofocal lenses, toric lenses can be used to correct for distance vision; providing perfect distance vision EVEN with astigmatism.
But toric lenses can also be used with a technique called mini monovision or monovision in order to get out of glasses for computer and reading as well.
How can we take an inflexible lens that only has a single focus and use it to get out of glasses? Well, using both of our eyes helps solve this problem.
With monovision, one eye is corrected for distance vision and the other eye is corrected for up close reading vision. This allows for both eyes to work together to cover a much larger range of vision. In many cases, monovision is able to get individuals out of reading glasses for everything but tiny print.
Of course, this isn't the natural way we use our eyes. But our brain's ability to process vision has a remarkable way of adapting. Initially, the blur in the distance from the eye focused up close will be very obvious and also cause extra night time symptoms. But gradually over months through a process called visual neuroadaptation, these extra symptoms become less and less noticeable until vision becomes seemless and natural. (See also Adjusting And Training Eyes After Cataract Surgery)
With a smaller prescription difference between the two eyes, this transition period becomes easier to adjust to without decreasing near vision too much; you may hear this referred to as mini monovision.
Monovision isn't unique to cataract surgery. In fact, monovision is also very popular with contact lenses to achieve the same goal and avoid the need for reading glasses, bifocals or progressive glasses.
But the key requirement with monovision is that each eye is corrected as maximal as possible. This means correcting astigmatism such as with toric lenses. This also means optimizing the health of the eye by treating conditions such as dry eye. And you will see that these are also necessary requirements for any of the premium lenses.
As with the monofocal lenses, each of the major manufacturers have their own toric lenses.
- Clareon Toric by Alcon
- Tecnis Toric II by Johnson & Johnson
- Envista Toric by Bausch & Lomb
Light Adjustable Lens
Before we move on from the single focus lenses, there is one more intriguing technology. A lens where the power can be adjusted AFTER cataract surgery.
Before cataract surgery, different calculations are done based upon the measurements of the eye in order to predict the exact power of artificial lens necessary to give perfect vision. But unfortunately these predictions aren't 100%. There are just limitations to our current technology. What this means is that approximately 5% of patients will end up off target after cataract surgery. An additional 20% may end up close but not close enough. Getting on target is especially more challenging for those who have had prior corneal vision correction surgery such as lasik, PRK, or RK.
A pair of prescription glasses or a laser eye surgery enhancement can take care of this residual prescription, but it would be ideal if we could eliminate any residual prescription.
That's the prefix for the light adjustable lens.
This lens is placed within the eye like any other normal artificial lens. And like any other cataract lens, the power of this lens is predicted ahead of time.
But if this lens ends up off target, UV light from a special machine can be applied directly to this lens to change the shape within the eye and correct prescription. Essentially, it is almost as much of a guarantee as it can get to getting vision perfectly on target after cataract surgery.
While this is a great way to obtain perfect distance vision (or monovision to get out of reading glasses as well), it does take some commitment after the surgery.
These UV light treatments occur starting approximately 2-3 weeks following the cataract surgery. As UV light exists everywhere, it is important to wear UV blocking glasses and sunglasses to prevent UV light from normal sunlight and even from indoor lights from inadvertently affecting this lens. In total, it can require about 3-5 UV treatments to fully optimize the lens. So, this lens has additional restrictions and visit requirements above and beyond what is normally required for cataract surgery - all in the name of getting the best vision possible.
The light adjustable lens is made by RxSight, an independent company from the big 3 mentioned previously.
Moving Beyond Single Focus Lenses
We are finally moving beyond the single focus lenses and into the realm of lenses that can reduce or even eliminate the need of glasses for the distance and up close.
The past two decades have seen more and more advanced designs and improved our ability to correct vision with cataract surgery.
The holy grail of a cataract lens is one which works just like our natural lens. One that has the ability to change focus just like how our own lens does. This is called an accommodating lens.
And technically an “accommodating lens” does exist and has existed since 2003. This lens is called the Crystalens and is made by Bauch & Lomb.
This lens is designed to change its position and thus its focus depending on whether we look off in the distance or up close. No fancy optical tricks required. Giving us that full range of vision correction.
Perfect right? Well, in reality, the accommodating effect of the crystalens is much more limited and inconsistent. While these lenses improve upon a single focus lens, it just doesn't provide enough of an effect to get out of reading glasses.
But to its credit, this lens is still used today, some 20 years later, in certain situations.
Since then, the criteria for a lens to be labeled an accommodating lens has become more rigorous. And the search for the near perfect replacement of our own natural lens continues.
Multifocal and Trifocal Lenses
Because science has yet to discover a way to make inflexible material behave exactly like the way our own natural lens does (and change shape), different optical techniques have been developed in order to give simultaneous vision for distance, computer and reading vision.
These particular types of lenses take light that enters your eye and focuses it for distance vision, reading vision and computer vision all at the same time. Instead of a single focus, these lenses have multiple focus points (thus multifocal). That way, no matter where you are looking, some of that light entering your eye will be in focus.
The current generation of these lenses can pretty much get you completely out of glasses. These are known as trifocal lenses because they focus for the three main distances that we look at: far away, up close and intermediate or computer distance.
There are two main trifocal lenses approved for use in the United States (and these two lenses are very equivalent):
Because of the special optical properties of these lenses, it does take some adjustment to get fully adapted to this alternative way of seeing. These are the small compromises in order to be able to have full vision correction without glasses after cataract surgery.
- In the short-term, one will notice an increase in night-time vision symptoms such as halos and starbursts. Similar to how the brain adjusts with monovision, the same occurs over time with these lenses leading to improvement in night-time vision over time.
- Rarely, one may also notice a slight fade or decrease in contrast in vision due to the splitting of light.
Because of the way these lenses work, anything that causes trouble with vision provides even more trouble with these lenses. Unhealthy eyes such as those with macular degeneration or with severe dry eye won’t do well with these lenses. In addition, higher than average amounts of distortions in vision, such as what can happen with prior corneal eye surgery, can also reduce the clarity of vision with these lenses. These lenses work the best for healthy eyes.
Extended Depth Of Focus Lenses
So what about those eyes that just aren’t healthy enough for trifocal lenses? This brings us to the final category of lenses.
Instead of splitting light into distance, up close and computer focuses (the multifocal lenses), extended depth of focus lenses seek instead to bend light to provide a continuous range of focus.
This allows for certain advantages:
- This avoids the night-time vision symptoms experienced with multifocal lenses.
- This prevents any reduction in clarity or contrast.
- This allows this lens to be used for the “less-than-healthy” eyes or with eyes that have had prior lasik.
But on the downside, this lens can’t provide the full range of correction that the current multifocal lenses can provide.
This lens can correct for distance and computer distance. But, when both eyes are corrected in the distance, reading glasses will more than likely be required to see up close.
To improve the reading vision with these lenses, it is common to intentionally shift the focus of one of the eyes towards computer and reading vision. If you remember from above, this technique is very similar to monovision or mini monovision. The only difference is that with extended depth of focus lenses, only a small shift is needed. This in turn may be labeled as micro monovision to indicate the small difference in prescription between the two eyes.
The true extended depth of focus lens approved for use in the United States is the Vivity by Alcon.
But there is another lens to mention. This lens is called the Eyhance and is made by Johnson & Johnson. This lens has some extended depth of focus properties but technically doesn’t extend the vision as far as necessary to fully qualify as a true extended depth of focus lens. Thus, this lens is still considered a monofocal lens.
Which Lens Is Best?
With the diversity of lens choices available, it can be difficult to figure out which lens is best for your eyes and vision after cataract surgery. There is no one lens that rules them all. Fortunately, you don’t to make this decision alone; your cataract surgeon will also help guide you to the best option for your eyes.
- If you are looking for the least amount of glasses possible and your eyes are healthy, then using a trifocal lens is the way to go.
- If you are a long-time user and well adjusted to monovision contact lenses, than having micro monovision with extended depth of focus lenses or monovision with light adjustable or toric lenses provides the most seemless transition after cataract surgery to glasses independence.
- Using extended depth of focus lenses with or without micro monovision is also the best bet if your eyes aren’t healthy enough for trifocal lenses and you desire as much glasses independence as possible.
- If you prefer the sharpest distance vision possible and don’t care about computer or reading glasses, than using light adjustable lenses or toric lenses are your best bet.
- If you don't mind glasses and want what your insurance is going to cover, than having a monofocal lens is a perfectly suitable choice.
And many of these lenses can even be mixed-and-matched, such as combining a trifocal lens with an extended depth of focus lens, to really customize your vision after cataract surgery.
Allowing you to get your best vision after cataract surgery
Lenses for cataract surgery include standard single focus lenses all the way up to mutifocal lenses capable of eliminating glasses and a wide variety of technologies in between. Each of these lenses excels in one way or another to give your vision a whole new life.
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