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Pursuit of ideal presbyopia-correcting IOL continues
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The options available for the surgical correction of presbyopia with an IOL implant continue to expand. The potential indications for the treatment of presbyopia also continue to expand. Every patient who undergoes cataract surgery is potentially a candidate for a presbyopia-correcting IOL if we had a technology that did not degrade quality of vision and retained stereopsis and binocular summation. In addition, because the etiology of presbyopia resides in the lens, it is patently obvious to both patients and surgeons that a lens-based solution is logical.
The defining of the so-called dysfunctional lens syndrome, which includes presbyopia along with a reduced quality of vision from increased higher-order aberrations, light scatter and reduced contrast sensitivity in the aging natural lens, has helped both surgeons and patients better understand the problem. Elective patient pay refractive lens exchange for the treatment of dysfunctional lens syndrome is becoming more common in many practices with high patient satisfaction.
We now have four categories of lens implants to use when treating presbyopia: the monofocal IOL, the multifocal IOL, the extended depth of focus IOL and the accommodating IOL. A few personal thoughts on each of these categories. As a disclosure, I consult with companies on products in all these categories.
Monovision or blended vision remains the most common approach to treating presbyopia in the U.S., accounting for as many as 25% of total patients implanted, or nearly 900,000 patients a year. I find this to be an excellent option, even in patients with mild ocular pathology. I always target between –1.25 D and –1.75 D of myopia in the near eye, and several well-done studies support this refractive target. Most patients tolerate either the dominant or nondominant eye as the near eye, and ocular dominance is difficult to determine in the patient with significant cataracts that are asymmetric. I like to do the worst cataract first and prefer to target this eye for distance. I then target the second eye for near. Excellent vision is required in the distance eye, and I find my enhancement rate to be 10% to 15%.
Patients want less than 0.5 D of residual sphere and cylinder, and 20/25 or better is needed for high patient satisfaction, so astigmatism management with a toric IOL or corneal relaxing incisions is a critical skill. I do not hesitate to do a LASIK or PRK enhancement, and my patients and I prefer LASIK when there are no contraindications. The near eye is more forgiving of mild astigmatism, which in itself can increase depth of focus, but laser enhancement here is also not unusual. About half of my patients will have a pair of glasses for occasional use, such as low contrast or night driving, but the other half say, “No, thank you,” when I offer this option.
In the multifocal IOL category, we now have IOLs that range from +2.5 D to +4 D at the IOL plane. The trend in the U.S. is to lower powered adds, as night vision symptoms, reduced contrast sensitivity and loss of intermediate vision are less and this seems to trump the reduced near vision. I worked with 3M when the first diffractive multifocal IOLs were developed, and we implanted adds from +2 D to +4.5 D. We found that, for most patients, +2.5 D to +3.5 D was the “sweet spot,” and for the American patient, satisfaction was highest in this range. With bilateral implantation and binocular summation at all distances, visual function is quite good even with implants as low as +2.5 D add, and custom matching with dissimilar adds in the two eyes is enjoying a resurgence in interest. Using so-called “staged implantation,” one can elect to use a slightly different IOL in the second eye to fill in a perceived vision gap in many patients. In the multifocal category in Europe, trifocal implants are replacing bifocal implants, and I look forward to seeing these lenses make their way into the U.S.
Extended depth of focus (EDOF) IOLs are also garnering interest. I worked with eyeonics and later Bausch + Lomb to develop a refractive EDOF IOL on the Crystalens platform called the Crystalens HD. We placed a blended 1.5-mm center add of approximately 0.9 D on the Crystalens optic. Near vision was enhanced with retention of excellent distance and intermediate vision, but there was some loss of contrast sensitivity and a mild increase in halo. This lens achieved FDA approval but failed in the marketplace, confirming how important quality of vision is to patients and surgeons. The next likely U.S. approval in the EDOF area is the Symfony (Abbott Medical Optics). This sophisticated lens implant utilizes diffractive optics to create a 1.5 D add, which enhances near and intermediate vision. Quality of vision has been enhanced through an optic design that eliminates chromatic aberration and spherical aberration and has a high Abbe number. This lens implant is now available in Europe, and it will be interesting to see how it does in competition with the diffractive trifocal IOLs.
While the jury is still out, trifocal IOLs seem to be the market leaders to date. A new EDOF IOL that gives a seamless range of vision from distance to near is in development by AcuFocus, using the same small-diameter aperture optics utilized in the recently FDA-approved Kamra corneal inlay. This IOL is quite promising, and while originally designed for unilateral implantation with an aspheric monofocal in the other eye, it may be a good partner for many of the multifocal and EDOF IOLs; even bilateral implantation is being reported with high patient satisfaction.
Finally, the holy grail remains an accommodating IOL with a 2.5 D or greater accommodative amplitude at the spectacle plane. The Crystalens achieved accommodating IOL approval from the FDA by demonstrating improved intermediate and near vision without correction and a 1 D increase in depth of focus. Whether the Crystalens is an accommodating IOL or the first EDOF IOL, I have found in my patients that uncorrected near and intermediate vision are enhanced while retaining normal contrast sensitivity with minimal increase in night vision symptoms. Used with a “mini-monovision” approach, targeting one eye near plano and the other near –0.75 D, I have had excellent results and patient satisfaction with this IOL. It is popular in the U.S., where it places second behind standard monovision in popularity, but less popular in Europe where trifocals and the newer-generation EDOF lenses such as the Symfony are available.
We are all excited to access an accommodating IOL with greater accommodative amplitude, and the PowerVision and AkkoLens products are working their way through the regulatory barriers, and a few others are in early development. In a separate category, the electronic IOL originally pioneered by Elenza may rise again through the collaboration between Novartis/Alcon and Google.
I know what I want for my cataract surgery. I want to see again like I did when I was a 30-year-old emmetrope. I had excellent vision at all distances with high-quality images and minimal night vision symptoms or glare. There is no technology today that can restore that level of vision, but I am excited about our growing number of options. In the career of the resident finishing training today, I see an accommodating IOL with a 3 D plus accommodative amplitude, high-quality aspheric and achromatic optics, a good ultraviolet and perhaps violet light absorption for safety, a surface treatment that eliminates posterior capsule opacification and retains capsular elasticity, and adjustability to plano ±0.25 D of refractive target with no corneal surgery required. As long as the innovation cycle continues to attract investment, there is no reason this goal will not be achieved.
Disclosure: Lindstrom reports he is a consultant for AcuFocus, Abbott Medical Optics, Alcon, Bausch + Lomb, Calhoun Vision, Elenza and NuLens; receives royalties from AcuFocus and Bausch + Lomb; is an investor in AcuFocus, Abbott Medical Optics, Bausch + Lomb, Calhoun Vision and NuLens; is on the speakers bureau for Alcon; and is a patent holder with Alcon.