Hello I'm Adrian West. I am a comprehensive ophthalmologist at the University of Michigan Kellogg Eye Center. I'm speaking today on intraocular lens material and design. Let me start first with a history of intraocular lenses. The original intraocular lens was created by Sir Harold Ridley. Sir Harold Ridley had noted that pilots were returning from World War Two with pieces of plane canopy in the eye, and they were tolerating the material quite well. This canopy was made of poly(methyl methacrylate). He therefore decided this might be a good material to try for the first intraocular lens. He had some ideas that were quite good and that he designed a lens that basically was similar in size and shape to the natural lens. This first lens lacked haptics. It was associated with some problems. Patients tended to have chronic inflammation in the eye because it lacked haptics, there was occasionally occlusion of the pupil. There was significant posterior capsular thickening noted in many of the patients. Iris atrophy and general Malpositions of the lens implant occurred over time. Here is a diagram showing the first Ridley lens. You'll see that it is round and again, it lacks haptics. The lens was particularly heavy relative to a natural lens as well. Next we move into the second generation of lens implants, and at this point most cataract surgery was being performed with an intra capsular technique so that there was no remaining posterior capsule to hold the lens implant. These lenses were therefore being placed in the inter chamber and they were considered somewhat simpler to place compared to the previous posterior chamber lens implant. The problem with these lenses is they were associated with uveitis glaucoma hyphema syndrome. The edge of the implant tended to erode into the vessels located in the inter chamber angle and patients suffered from chronic inflammation as well as spontaneous hyphemas. In addition, these lenses frequently lead to corneal failure over time. Here are some images showing anterior chamber lens implants with nylon loop haptics. The obvious problem with these lenses was that nylon is noted to degrade in water, which is the main component of aqueous. Therefore these lenses tended not to be stable in the interior chamber over time. The third generation lenses are now anywhere from the early 1950s into the early 1970s and this is yet another completely different design in which the iris was used to support the lens. The diagrams below show some of the designs of iris clip lenses and this top image shows how that lens was held in place around the iris. These lenses had constant Iris contact and ultimately lead to pigment dispersion as well as chronic inflammation. The fourth generation of lenses are shown here with many examples of anterior chamber lens implants. The lenses on the left are examples of Kelman anterior Chamber kens implants and you will note that lens D is very similar to the modern anterior chamber lens. All of these are open loop haptics so that the haptics are quite flexible and this flexibility allows the lenses to be very well-tolerated in the anterior chamber. Lenses on the right are some of the other versions of the anterior chamber lens implants that were briefly in use. These lenses all have closed loop haptics so that the haptic attaches on both ends. These lenses were all associated with corneal endothelial failure and issues with chronic inflammation. The fifth generation of lenses also include lenses for posterior chamber implantation with prolene haptics or three piece lenses that allow the lens to be stable in the capsular bag. We see some familiar looking C loop and J loop type lenses on the right. And finally, we get up into the sixth generation or what are considered the modern currently in use lenses. So these were first developed and introduced around 1992, and these lenses are designed for placement into the capsular bag. We have small single piece lenses, we have lenses with three piece- meaning that the haptic and the optic are made of different materials. These lenses can now be foldable and placed through smaller incisions into the capsular bag. Again, we're still using the common very flexible open haptic anterior chamber lenses. These are still in widespread use when indicated, and we also have different options with refractive lens implants available, although we'll go through those later in the talk. So next, let me speak briefly of some of the different properties of lens implants. First let's consider the refractive index. The refractive index is the speed at which light travels through the material. The human lens has a refractive index of 1.39. Silicone is a material that most closely mimics the human lens and hydrophilic acrylic, PMMA and hydrophobic acrylic have greater refractive indices than does silicone and the human lens. There are several commonly used lens materials in use today. Let me first speak about silicone. Silicone was actually the first foldable intraocular lens material available. Again, it has a low refractive index- very close to the natural human lens. It is hydrophobic, so when you receive this lens in the operating room, you will open up the package and it is packaged dry. Silicone has a couple of interesting properties, but it does tend to deliver rather forcefully into the capsular bag. It opens pretty quickly compared to some of the other lens materials. In addition, the capsular bag has a rather fibrotic response to silicone and you will see more posterior capsule opacification. There are many lenses available made of silicone including the more recent crystalens. So here are two basic designs available in silicone lenses. The original was the plate haptic design. So this one piece lens has two large fenestration holes and those allow the surgeon to position that lens and rotate it appropriately in the capsular bag and they also help the interim poster capsule leaflets to adhere to one another through the fenestrations. This may help with long term stabilization. One problem with plate haptic silicone lenses is that they too have a tendency to dislocate after YAG laser capsulotomy. The multi piece silicone lens has haptics made of polypropylene and again is placed in the capsular bag. So here on the left is an example of phimosis of the capsule. You'll see that the- what looks initially to be the pupil, is actually the internal edge of the entire capsule where it has constricted and are pacified around the lens implant. In addition, silicone lenses do tend to have a reduced functional optic, and therefore may not be the best choice in patients with large pupils. Hydrophilic acrylic lenses are also known as the Hydrogels. They are made of hydroxyethyl methacrylate. They have a high water content and therefore tend to be packaged in the wet state rather than dry. They are also foldable for small incision use. Studies do indicate that they have a higher rate of lens epithelial cell proliferation and cell growth meaning that you have a higher rate of needing a YAG laser capsulotomy later on. They also have an unusual quality and that some of these have been known to calcify in vivo- in patients so much so that they need to be explanted and replaced with a different lens. Again, there are several commonly available hydrogels. The MemoryLens, Hydroview and Collamer are some of the frequently used lenses in the United States. Again, we have a slide here showing opacification and capsular phimosis and fibrosis associated with this type of lens. The hydrophobic acrylic lens is a lower water content, so this lens is packaged dry. It has some structure chemically based upon the poly(methyl methacrylate) of the original intraocular lens implants. It has a relatively high refractive index and again it is foldable for small incision use. This lens has a very nice gentle slow unfolding that eases the use in the operating room. There does tend to be a greater amount of lens epithelial cell regression and the lens tends to adhere quite nicely to the capsular bag and this reduces the likelihood of having enough capsule opacification later on that the patient would require YAG laser capsulotomy. They Alcon line of lenses, the Acrysof lenses, are all in this hydrophobic acrylic group as are the others that you see listed. So here at the University of Michigan Kellogg Eye Center, we primarily use the Alcon line of lenses. The Acrysof natural lens that is imaged here was first approved for use by the FDA in June of 2003. You'll note that it has a yellowish tint to the lens. The yellowish tint is intended to block out some of the blue light of the visible spectrum of light. What is blue light? Well, it's light somewhere in the mid 400 to 500 wavelength range and it is actually found all around us. When you're out in the sunlight, around computers, office lighting, lasers etc. These are all sources of blue light. And why has blue light concerning? As we age, the retinal pigment epithelium tends to accumulate pigment called light lipofuscin. Lipofuscin does absorb blue light and when it does, free radicals are formed. This is known to be toxic to the retinal pigment epithelial cells. These free radicals lead to death of these cells and they're no longer available to nourish the photoreceptor cells in our maculas. This is thought to perhaps lead to macular degeneration. Therefore, it may be desirable to block blue light absorption in the retina. The Alcon AcrySof natural lens is designed to mimic the blue light filtering properties of a middle aged human crystalline lens. Bausch and Lomb has a competitive message. They filter out the violet end of the spectrum. Their thoughts are that night vision is not as compromised when one blocks out the violet rather than the blue. And in addition there have been studies indicating that perhaps blue light is important to our natural circadian rhythms and sleep patterns. We all know that there are frequently complaints among the elderly about difficulties with sleep and perhaps it is not beneficial to block out the blue light as a result. Let me speak also about aspheric lenses. This is a relatively newer technology as well. And you'll note in this slide, in the top left, a natural human lens when its young, allows for light images to pass cleanly through to one sharp point of focus on the retina regardless of what portion on the lens that light passes through. As we age, there is more aberration in the lens and light starts to come to different points of focus within the eye as it passes through the peripheral versus the central lens. This degrades the quality of the image that we see. Traditional lenses are spherical, and unlike a younger lens, we again have light coming to focus at different points in the eye and that leads to a less sharp image. The newer lenses that are aspheric account for this and allow light passing through the periphery of the lens as well as light through the center lens to come to one sharp point of focus on the retina. This doesn't prove the clarity of the image. Let me now speak a little bit about some of the different refractive lenses that are available. The Acrysof restore multi-focal is a lens that allows patients to have both good distance and near range of vision without eyeglasses. It relies upon a technology called apodization and diffraction. This is a gradual reduction or blending of defractive step heights along the lens. You can see the different rings on the lens as you look at the image. So diffraction refers to the spreading of light to create multiple images and then the retina and the brain help to sort out which image the patient is paying attention to through that lens. The center zone tends to give patients more of the intermediate and near range of vision, whereas the more peripheral rings are providing the more distant portion of the vision. These lenses tend to be relatively good at near, but less good out at arm's length distance such as the computer range. 80 percent of patients reported being eyeglass free in trials most of the time for most of their activities. There are drawbacks to this particular lens in that patients do tend to experience some glare from bright lights or headlights at night and the sharpness of the vision is not as good at night. The AMO Tecnis multi-focal is a direct competitor for that lens. This lens is similar and that you can see rings of power on the lens. It is somewhat better for intermediate distance, but not quite as good at near than restore lens. In general 92 percent of patients reported that they never needed to wear glasses or rarely wore glasses for different activities. The technology here is somewhat different. It's relying on zonal refractive optical technology. Again, patients experience glare with this type of lens and decrease night vision. This particular lens tends not to function as well with smaller pupils. A third alternative is the Eyeonics Crystalens HD. This is a completely different style of lens and it relies upon hinged areas on the lens to allow flexing of the lens. So when a patient attempts accommodation, the lens can flex and move forward anteriorly in the eye, allowing a different point of focus on the retina. This gives patients near vision as well as distance vision in the relaxed state. In an FDA trial 98 percent of patients were able to read standard news print size with this lens. Again, it has a smaller optic so it may not be ideal for patients with larger pupils. There is a greater incidence of capsular phimosis and surgeons report it somewhat harder to predict post-operative refraction with this lens. In general a surgeon needs to be very careful in selecting which patients to use any of these lenses. The lenses in general may not provide quite as crisp and sharp a vision as a traditional lens and hypercritical patients may not appreciate some of the benefits of the lens but be more focused on some of the shortcomings of the lens, because our first two lenses create a significant amount of glare. Patients who come in the door in your office complaining about glare or lifelong glare intolerance may not be at all happy with the residual glare experience with some of these lenses. Patients with previous Radial Keratotomy surgery also already have significant glare to start and this will be additive. In addition it can be harder to predict their post-operative refractive outcome. These lenses can be more difficult to look through in examining patients with retinal disease as well. So one should be careful in selecting a lens for patients with potential for retinal disease. Finally, let me speak about toric lenses. These have also been relatively recently introduced and they are now available for correction of astigmatism. There are positioning marks on the edge of the lens implant that allow you to line up the lens with previously marked axis on the surface of the eye. The lenses otherwise behave in a similar fashion to the other Acrysof lenses for insertion through the smaller incisions. In summary, we have many options available now for today's modern cataract surgery patients. Now more than ever it is very important to have a discussion with patients about what his or her expectations are regarding final refractive outcome following cataract surgery. Thank you
