This discussion is about the latest technology for implants at the time of a cataract procedure is complicated, and to understand what is available, one must know some basics about the procedure itself. A cataract means the normal human lens has gotten cloudy, and a new artificial lens is used to replace it. This is a normal part of aging, and if one lives long enough one will get this surgery done almost universally. When we are young, the lens can change its shape; Therefore, if one can see the 20/20 line in the distance by whatever means (glasses, contact lenses, after LASIK, or if God made you see without glasses well in the distance), then in your early 40’s, we all start to lose the “zoom ” capability, so that reading glasses or bifocals are needed. By age 60, almost all “zoom ” is lost, so a person who sees 20/20 in the distance can’t see well up close at all.
Currently, there is no perfect replacement for the normal young human lens. All implants used today have various good points and drawbacks, and your Doctor will help you decide what option is best for you. This is based on your desire for independence from glasses, and how you use your vision on a daily basis. For instance, an over the road truck driver, who needs to see well in distance at night, might select a different implant than someone who wants to read well without glasses. I will discuss the options available in this blog, but first you need to understand various concepts to understand your choices.
Standard Surgical Results
We are pretty good at giving people what they want, but the state of the art is not perfect. With standard, manually done surgery, the very best surgeons get 70 % or so of their patients without glasses to see the 20/30 line or better. The 20/20 is our goal, but at 20/30 or better, people really generally functional for distance for most tasks including driving. I like to call this, 20/ happy…….this is in persons who have no ocular disease, and without significant astigmatism. This of course means 1/3 are more dependent on glasses for optimal vision; if they were 20/ 200 without glasses for most of their lives, a person who is now 20/ 40 is typically very happy, but we have not achieved perfection either.
Historically, surgeons 10 years ago or more were happy with best corrected vision to be 20/20, and independence of glasses was a nice thing but not necessarily the goal. Now we try for a home run rather than a single…. the best possible vision without glasses. New technologies are developing to deliver this goal, and we are constantly improving…but still not perfect. Insurance will pay for manual cataract surgery and for standard implants, but most of the technology needed to predictably get good uncorrected vision is NOT covered; in other words, insurance is only wanting to pay for procedures that will get you to you 20/20 if possible, but don’t care if you need glasses or not to get there…. Therefore, to improve your odds, the patient has to pay out of pocket for these new technologies. The amount can vary according to what is needed to achieve this goal, something we will discuss further.
Review of Optics
Now, a brief lesson in optics…. people who are ” normal”, we call “emmetropic”…they see 20/20 without glasses, and the optics of the cornea and lens focus light coming in to the retina in perfect focus. Then, for reading, the lens changes its shape to a near focal point, like the lens of a camera. The cornea acts like the window in the front of the eye and is the main refractive component of your optics, while the lens inside the eye provides the fine tuning for the distance and near vision. Near sighted people (myopic) can see up close well, but cannot see well in the distance without optical correction. Far sighted (hyperopia) people see well in the distance, but cannot see up close as well. In myopia, the eye itself is too long, while in hyperopia, the eye is too short. Optical correction is then used to bring the focal point to the back the eye, to the camera film that we call the retina, for optimal vision.
Astigmatism is a bit more complicated. It means that the optics of the eye are shaped more like a football shape rather than a basketball shape, and is optically corrected with lenses that have a fold in the opposite direction to clearly focus light on the retina. We all have astigmatism; the question is how much. Also important is where the fold is located, at 90 degrees (vertical) or 180 degrees (horizontal) or midway between the two, such as 55 degrees (oblique)….correction in the eye, or with a contact lens on the surface of the eye can correct astigmatism without distortion…but….correction with glasses can induce a ” funhouse mirror effect”, where images can look distorted, such as a table looking slanted on one end. This can take days, weeks, or never resolve; hence correcting astigmatism on the eye itself is optically superior than glasses.
Whether someone has an astigmatism or not, correction of myopia or hyperopia also induces a “prism ” effect, with the stronger the lens the more distortion is induced. People who are corrected to 20/20 with either glasses or contacts or cataract surgery say that they see better with correction being inside (as with lens replacement) or on the surface (as with contact lenses) rather than with glasses. If you also have an astigmatism, this compounds the distortion effect. Therefore, correction of astigmatism results in better quality vision if done at the time of a cataract procedure than with glasses after surgery.
Why Optic Results After Surgery Can Vary
So why don’t we get 20/20 in everybody? In our pre-operative measurements, we know very well the length of the eye…. we do a map of the cornea, like a topographical map, which tells us pretty well about the shape…. we know the optical power of the lens we put in….so, using mathematical formulas, we should be able to get very accurate results. The problem is, we are dealing with biological systems and not camera lenses; there are variability of the optics that we cannot predict.
For instance, the incision for the surgery itself induces astigmatism; this is somewhat predictable and can be factored into the formula, but it is not rare to get a surprise amount after a perfectly done procedure. Further, we don’t have a way to predict where the bag of the lens comes to rest; the implant is placed into the skin (capsular bag) of the human lens, which is clear like cellophane, which then shrink wraps the lens in place after a month or so….and it may shift more forward or backwards than we predict, resulting in more near or far sightedness than we would think…there is some biological imperfections in our optical systems we cannot fully predict or understand; for example, the optical axis, the line in the very center of our vision, is typically not going through the very center of the lens system of the eye, typically being a little nasal to the optical center of the cornea. As you might expect the amount can vary from person to person, which we can’t fully predict……In summary, we are pretty good, but not perfect; and probably never will be perfect.
So, let’s suppose you get a big “surprise ” in your desired refractive outcome? Well, the good news is it can be fixed …. for instance, LASIK can be done…or if the spherical power is way off, the lens implant can even be exchanged, best done a month or so after…lens exchange is covered by insurance, but poses the risk of intraocular surgery. LASIK is safer and more predictable, but is NOT covered by insurance, typically costing around $2000 per eye.
Lasik Vs. Cataract Surgery
So what is the difference between LASIK and cataract surgery? Both aim to give good uncorrected distance vision…but LASIK doesn’t work well for near vision purposes, while a lens replacement with a multifocal implant can give good distance and near vision…. LASIK reshape the cornea; Cataract procedures exchange the lens for a new lens. Removal of the cataract requires going inside the eye and therefor has a higher risk for vision threatening complications, and since LASIK is done on the surface of the eyes and therefore safer. Of course LASIK won’t work if you have a cataract. LASIK is more accurate than cataract surgery in its refractive results, so it works very well if a touch up on the cataract results are needed. LASIK is done on younger people (20’s and 30’s) and lens removal on older folks (50’s and older). I am not going to discuss LASIK in detail, we’ll do that in a future blog.