One of the beautiful things about cataract surgery in modern times is the ability to see well without being dependent on glasses. Thanks to advancements in technique and technology, we are getting LASIK like results. A lot of patients have worn glasses their whole life, so the idea of not needing them is very exciting. The 2 most common methods for glasses independence after cataract surgery are Multifocal Lenses and Monovision correction. There is another class of accommodating lenses that I will cover only briefly since they tend to not be as predictable as the other 2 options.
As you can imagine, multifocal lenses DO NOT work like your God given lens. The lens you were born with is actually quite amazing. When you’re young, your lens is the consistency of jello and can easily change shape. When you look off at a distance, your lens is relaxed and it allows all the light at a distance to focus on your retina so you can see clearly. When you read up close, incredible things happen, your eyes come together, your pupils get smaller and your lens physically thickens to effectively create a magnifying lens allowing you to read even the smallest print up close. We refer to this as accommodation.
As we get older we begin to lose that ability to thicken our lens (accommodate) and become more and more dependent on readers then bifocals then ultimately we need cataract surgery. Ideally, we would be able to put a lens in the eye that mimics the human lens but we are not there yet.
If you look closely at a multifocal lens, you will see all these little concentric rings around the center. The space in-between these rings acts like little prisms, each bend light a little differently. When the lens is inside the eye, it takes all the light that comes in and splits it up. Most of the light is dedicated to distance vision while the rest is dedicated for near and intermediate. These lenses work best when both eyes are implanted since our brain is wired to use both eyes together.
The Good and the Bad
Although multifocal lenses are the best option for getting you out of glasses for most things, they are by no means perfect. Remember these are mechanical lenses so they do have limitations. Because they split light, you sacrifice some details at distance and reading vision is highly dependent on good lighting. The rings in the lenses also create halos at night which ALL patients see initially. One interesting aspect is that within a few weeks to months most patients adapt to the halos and simply don’t recognize them.
When I speak with patients about multifocal lenses I must first make sure that there are no other issues causing blurry vision such as glaucoma, macular degeneration or scars on the cornea. If it looks like the patient is a good candidate there are a number of points that I like to make sure patients are fully educated on. First the multifocal will allow you to see just about everything you want to see without glasses but here are the things you MUST be aware of moving forward.
- You WILL see halos at night for up to 6 months and possibly longer. Most patients they resolve within 6 weeks some take up to a year.
- Good lighting is mandatory for good near vision. You will NOT see well up close in poor lighting conditions, ever. You will want to wear readers at first which is fine. Almost every patient wears readers initially then over time, as the brain adapts to the optics of the lens, you will use them less and less.
- There is a slight loss of contrast sensitivity at distance. This simply means that even though you may be 20/20 or better at a distance, fine details may not be as sharp as with a distance only standard lens. This is generally not an issue, since patients with significant cataracts don’t see well at distance or near anyway so any improvement is wonderful.
- There is a chance that you may need a LASIK enhancement after surgery. When someone pays for a multifocal lens, they aren’t paying for a lens they are paying for a result. Even though cataract surgery is very accurate now a days there’s still 1 in 20 or so that may need a “touch up”. Good news is that LASIK after cataract surgery is incredibly precise and in our practice, it’s included with the surgical fee (kind of like a warranty).
- There is a slight chance that your brain will not adapt to the optics of the lens. This is very rare, probably 1 in 2000 but it does happen. Patients who experience this will be 20/20 at a distance and can read the smallest print up close upon exam but will swear they can not see. If this occurs the best treatment option is a lens exchange for a non multifocal. We allow all patients to neuro-adapt for at least 6-12 months before talking about a lens exchange.
All that being said, multifocal lenses are still wonderful. The vast majority of patients are incredibly happy and love their “new eyes”. Very rarely do we see situations that require intervention and as long as you know going into it that there is a period of adaptation it makes the process much better.
Monovision, or blended vision, is when we correct one eye for distance and the other eye for near. The brain simply takes both images and blends them together. The goal of monovision is to eliminate the need for reading glasses. It is a common practice with contact lens wearers after the age of 40, which is when most of us begin to need help with reading. As patients begin to lose their near vision, the non-dominant eye is made slightly nearsighted to put that eye into near focus. Most patients tolerate this well and do not require glasses for most tasks. Sometimes patients can not adapt to the discrepancy but this is unusual.
Even monovision has its drawbacks. Because each eye has a different image, there is a loss of depth perception which can cause a little trouble judging distance. The biggest issue we encounter with monovision is night time glare. The distance eye does fine with light but the near eye sees a pinpoint of light like a cotton ball. This can cause dramatic symptoms especially while driving. Not everyone has trouble but the most common reason a monovision patient wears glasses is for night time driving. During the day and in bright conditions the vision is great!
Monovision is best suited for patients who have worn it in contact lenses for many years because we know they have adjusted to it. It is not uncommon for patients who have never worn monovision to try it for a day or so in contacts to see if they can adjust to it. If after surgery, a patient can not adjust to monovision, LASIK can be performed to balance the vision.
Monovision can be accomplished with either the standard lens or a toric lens depending on how much astigmatism is present.
Accommodation is the process that occurs inside your eyes when you focus up close. This happens because of a muscle that is attached to your lens bag. When the muscle contracts, your lens changes shape (thickens) which causes you to become more nearsighted.
An accommodating lens is hinged at both arms. These hinges allow the central optic of the lens to move back and forth during accommodation. The resting position of the lens is optic back and arms forward, this configuration allows for good distance vision. When you look up close and accommodate, the optic of the lens is pushed forward and you become more nearsighted which allows you to see up close.
Image courtesy of Bausch and Lomb
In theory, an accommodating lens should be the perfect option, sadly it is not. The range of vision with these lenses is not stable enough to ensure a stable outcome. Some patients see very well distance and near while others still need readers for everything. The human body is dynamic and some patients heal differently than others, the outcomes of these lenses is so unpredictable that I only use them in rare situations.