Special Lens Implants to Reduce Your Need for Spectacles

By David F. Chang, MD

Some people mistakenly believe that having cataract surgery will enable them to see perfectly without glasses. Having the eye's natural cataract-clouded lens removed and replaced with a clear artificial lens implant should certainly improve your vision. However, the conventional artificial lens is a single, fixed focus lens. It cannot give distance focus one moment and near focus the next (like the eye's natural lens does in a young person). Thus, even after cataract surgery, eyeglasses are still needed in order to shift the focus of your eye.

While we're young, the “focusing” muscles inside our eye are able to change and control the shape of our natural lens. This change in lens shape allows us to shift our focus from far to near. This natural focusing ability is called accommodation. Like the auto-focus on a camera, accommodation is so fast and automatic that we're not even aware that it's happening. However, the eye's natural lens hardens as we age. As it loses flexibility, we progressively lose our accommodation. Presbyopia is the term describing the natural and unavoidable loss of this far-to-near focusing ability over time. By our 40s, the diminishing ability to focus up close must be replaced with reading glasses, bifocals, or trifocals. This is why even laser refractive surgery, such as LASIK, can only eliminate glasses if you are under the age of 40. Standard intraocular lenses cannot replace this age-related loss of accommodation or the need for reading glasses either.

You may also need eyeglasses to correct your far distance vision following cataract surgery. The artificial lens comes in more than 60 different powers. Since there is no opportunity for trial and error in selecting the lens implant for your eye, there is no guarantee that perfect distance focus will be achieved with surgery. Astigmatism is another reason that distance glasses may be needed at times. The lens implant does not correct astigmatism, which is a natural blur resulting from the shape of the cornea. Fortunately, eyeglasses can be used to optimize distance focus just as they do for anyone whose eyes are not in perfect focus naturally.

It is important and reassuring to remember that after cataract surgery, you should have the same optical options available to everyone else over age 50 who has never had a cataract. These include bifocals and trifocals, separate reading and distance glasses, contact lenses (including monovision), and even refractive surgery such as LASIK. However, the goal with standard cataract surgery is to avoid the need for you to wear thick, strong prescription glasses afterward.

Multifocal Lens Implants

There is one special type of lens implant – the multifocal – that provides both near and far focus simultaneously and can significantly reduce your dependence on reading glasses. The term multifocal stands for “multiple focal points”. Standard lens implants are called monofocal lenses because they set the focus at a single location and cannot provide the ability to see at multiple different distances without glasses.

Multifocal lens implants are designed to produce a dual focus. Part of the lens is set for distance focus, and part of the lens is set for near. The design is entirely different from bifocal eyeglasses where you look through the top portion for distance and the bottom area for near. With a multifocal lens implant the brain automatically finds the correct focus.

Like the standard lens implant, the multifocal is a foldable lens that is implanted through an extremely small incision and is equally safe. However, compared to a standard lens implant set for distance focus only, a multifocal improves your ability to see up close without glasses. Not everyone with a multifocal lens implant can read equally well without glasses. There are many factors that cause this individual variability. The ability to read without glasses is certainly better if both eyes have a multifocal lens. The younger and healthier the retina is, the better the reading ability will be. Interestingly, the ability to read without glasses improves over time for most patients. It seems that with the multifocal lens system the brain learns to perform better with practice.

Because the lens implant does not correct it, any astigmatism you have will reduce your ability to see both far and near without glasses. Having a very small pupil size can also compromise your near function by limiting the incoming light. While there is no guarantee that you will read as well without glasses as you desire, multifocal lenses give you much better odds of doing so, compared to standard lens implants.

Can these special lens implants eliminate my glasses altogether?

This is unlikely. Most people with multifocal lenses still find it easier to read with glasses under certain conditions, such as for prolonged reading, for small print, or when the lighting is poor. While the multifocal lens implant won't totally eliminate reading glasses, it should provide the convenience of reading many things (e.g. handwritten notes, price tags, receipts, photographs, menus, and an airline boarding pass) without having to put on glasses. With reading glasses on, you should see equally well with a multifocal or a standard lens implant.

Depending upon the amount of detail you need to see, glasses to further sharpen your distance focus may still be worn for some activities. However, compared to standard lens implants, multifocal lenses will provide you with a greater and expanded range of focusing ability without glasses.

What about the cost?

Not surprisingly, the multifocal lens implant procedure is more expensive. Health insurance, such as Medicare, covers the costs of cataract surgery with a standard lens implant. However, the additional premium charge for implanting these special lenses is not covered, and must be paid out-of-pocket by the patient. Remember that the benefits of multifocal lens implants are to reduce the inconvenience of having to wear eyeglasses full time. They are not “medically necessary” because they have nothing to do with improving the health of your eye.

Is the Multifocal lens implant right for you?

While the multifocal lens implant should reduce your dependence on eyeglasses, there are some tradeoffs in addition to the added out of pocket expense. The different focal zones of the lens optic can create the appearance of halos or ghost images around lights at night. While a distant streetlight should be in good focus through the far-focusing portion of the multifocal lens, it appears blurry through the near-focusing portion of the lens. This creates a slight ghost image around the edges of the light. Such haloes are not evident during the daytime when your pupils are smaller.

Fortunately, seeing halos is a distraction that doesn't obscure the focus, and the vast majority of patients grade them as being “minor” or “minimal”. The halos will become much less noticeable over time as your brain gradually adapts to them. This is similar to the way in which your brain blocks out background noise, such as street traffic sound, over time. However, not everyone can adapt as easily as others. In the rare event that the haloes are too bothersome, the multifocal lens can be surgically removed. Because this entails risk, this is more of a last resort.

The multifocal lens implant isn't right for everyone. It doesn't work well if a person has significant astigmatism, or other problems involving the cornea, retina, or optic nerve. For several reasons, patients who have previously had refractive surgery, such as LASIK or radial keratotomy, are not good candidates. Finally, your individual lifestyle and activities should be considered. If you were unusually sensitive to glare before ever developing a cataract, then this lens may not be as ideal.

Reducing the need to wear glasses is not a priority for everyone, and since there are some tradeoffs and added costs, the multifocal lens implant would not be important for these individuals. Remember that both multifocal and standard monofocal artificial lenses will provide excellent vision with glasses following cataract surgery. The difference is in what you can see when you aren't wearing glasses.

The newest generation of Multifocal lens implants

The first multifocal lens implant was introduced in the late 1990's. This first-generation design had one important drawback – the presence of significant glare and haloes at night – which limited its popularity. The newer “latest generation” multifocal lens implants have been re-engineered and significantly improved. These newer multifocal lenses have far less tendency to cause bothersome haloes compared to the original designs.

Accommodating Lens Implants

Accommodating lens implants seek to reduce eyeglass dependence according to a completely different principle. Recall that accommodation is the natural ability of a young eye to focus by changing the lens shape. If the lens implant could also change its shape or position, some focusing ability could be restored.

The Crystalens implant was the first attempt to create an accommodating lens, whereby the eye's natural focusing muscles are able to cause some movement of the lens. This lens implant is hinged, to allow it to flex slightly. However, there is significant individual variability in the ability of the eye muscles to move the implanted lens. While the Crystalens does increase ones capacity to change focus relative to a standard lens implant, the ability to read without glasses has been more inconsistent and unpredictable from one patient to the next.

What will the future bring?

The development of new lens implants has been one of my own research interests for many years. In addition to having extensive experience with these special lens implants, I continue to be involved with several clinical trials and companies investigating new approaches. With respect to multifocal and accommodating lens implants, I am considered a national authority, and I frequently publish or lecture on this subject to other cataract surgeons. Unlike for standard lens implants, in order to use multifocal and accommodating lenses, eye surgeons must first become certified by the manufacturer through a process of training courses and submission of outcomes. For both the multifocal and accommodating lens implants, I was among the first Northern California ophthalmologists to become certified. If your eye surgeon has not been certified to use each of these special implants, you may not be offered all of these options.

Unfortunately, it is not feasible to replace your lens implant if a newer and improved design comes along in the future. Therefore, if you already have a significant cataract, you must make your choice of lens implant based upon the best technology currently available.