"In the past few years, we've had a push toward foldable IOLs that we can place through a clear corneal incision, allowing us to use a topical anesthetic. Better design and better surgical technique are reducing the incidence of PCO from as high as 35 to 50 percent of cases, to less than 10 percent," notes Nick Mamalis, MD, Professor of Ophthalmology at Moran Eye Center, University of Utah.
What may be the biggest problem for surgeons is the sheer variety of choices in IOLs. In addition to polymethylmethacrylate (PMMA), the plexiglass first implanted by Dr. Ridley, there are three categories of lens materials. Within each category are various brands and designs, each of which seems to do something better than other products. Surgeons say they sort out the claims by focusing on what's most important.
"For the ophthalmologist, there are two things that are most important in an implant. The first is how it performs clinically for the patient. The second is how user-friendly it is. I'm talking about handling for the nurses, and ease of insertion: Is it a nightmare in the OR?" says Richard Tipperman, MD, of Wills Eye Hospital in Philadelphia, Pa.
The newer materials and designs all are more expensive than PMMA and are significantly higher in price than first-generation silicone IOLs. Yet some surgeons who have tried them say the benefits to patients make them well worth it.
"This is the implant I want in my eye," says Warren E. Hill, MD, of Mesa, Ariz., regarding the new Acrysof one-piece IOL. "There are no real limitations with this IOL."
Following is a review of some of the newer IOLs, divided by material.
This lens material has been in use for years, but we're now looking at second- and third-generation products. The new silicone lenses offer a higher refractive index, which means the lens can correct higher amounts of visual error without added bulk. These lenses also are more biocompatible, causing less PCO than PMMA implants.
ClariFlex with OptiEdge from Allergan is a third-generation IOL just launched this year. It offers a rounded edge that reduces internal reflections or glare. A rounded anterior edge scatters light, while the sloping side edge directs reflections away from the retina. A square posterior edge provides stability. Allergan's injection system implants the IOL through a 3-mm incision, and the folded IOL slowly unfolds in the eye. Another benefit of the injection system is that it prevents IOL contact with the wound and exterior of the eye, reducing the potential for postoperative inflammation.
CeeOn EDGE 911 and 913 were introduced by Pharmacia last April and October, respectively. Called "next-generation" silicone lenses, these IOLs have a higher refractive index, which is closer to that of the natural lens. Studies show that they diminish glare, and a special posterior edge diminishes the incidence of PCO.1 YAG capsulotomy rates for CeeOn are a low 3.5 percent.
A recent study of 180 eyes compared six IOLs (two versions of CeeOn, Hydroview, Acrysof, Sensar and MemoryLens).2 Results showed the incidence of PCO was lowest for CeeOn, particularly the 911, with its "sharp edge design." Patients who received CeeOn had a "good uveal and capsular biocompatibility one year after surgery." At this time, an injection system for CeeOn is in development.
PhacoFlex II from Allergan is the second generation of the PhacoFlex IOL. Allergan asserts that three studies show that this implant provides 20/20 vision for 96 percent of patients, and 20/40 vision for all patients. The company offers the same injectible implantation as with Clariflex.
Array from Allergan is a multifocal IOL that gets mixed reviews from surgeons, who, along with patients, love the idea of a visual correction for near and distance. But some surgeons say Array's performance is not consistent.
"It's hard to tell who the Array is going to work for. It does allow people to see up close and far away, but the explantation rate is high. I would rather do a moderate undercorrection in one eye. I call it ?monovision light'," says Dr. Horn.
Other surgeons have had better success with this IOL. "The Array has tremendous advantages for the interested or motivated patient. Distance vision is strong [with the Array] and the near vision continues to improve over time as neuroadaptation occurs. The disadvantage is the haloes and glare?these are tolerable and diminish as time passes," notes Avery D. Alexander, MD.
Staar Toric IOL attempts to correct another common visual problem-preexisting astigmatism. This lens is injectable through a small incision. In published reports, Staar surgical states that even in clinical studies, it provided uncorrected visual acuity of 20/30 or better for just 47 percent of patients.3 To get it to work right, surgeons must place the IOL very precisely and avoid rotating it away from its desired axis.
"If you have just a bit of unintended rotation, you can actually add astigmatism. It has a 10 percent explantation rate. What we need is a toric IOL in a one-piece acrylic design," says Dr. Horn.