As our journey into the 21st century progresses, we look more and more to new technology to solve some of the basic difficulties associated with aging. While the correction of presbyopia has been a major concern for hundreds of years, the more recent emphasis on refractive surgical solutions has led to several different technological approaches.
The traditional reading add and bifocal spectacle techniques are still prevalent, however we are seeing more and more reliance on combined modified mono-vision techniques, with or without contact lenses. Multifocal contact lenses, intraocular lens surgery and refractive astigmatic procedures are commonplace, but the lure of a truly simple and effective surgical solution to eliminating residual presbyopia has continued to entice the medical and scientific community.
Restor (Alcon), ReZoom and Tecnis (Abbott Medical Optics) are examples of multifocal intraocular lenses that are currently being implanted. Keep in mind that there is a significant financial impact—including the cost of implants and increased surgeon reimbursements— associated with multifocal lens insertion.
Crystalens (Bausch + Lomb) is a popular version of today’s accommodating intraocular lenses. All of these U.S. approved multifocal lenses work well in “good candidates,” with a small but vocal number of unhappy recipients. Thus, the rate of removal or replacement of multifocal IOLs is much higher than that associated with traditional single focus lenses. There have been no long-term studies of this issue but cataract surgeons agree that careful selection of patients is necessary. The more discriminating, younger engineer types may not be the best of candidates. Hence, while we are finding success with accommodating intraocular lenses, the number of suitable candidates remains limited. But, when you consider that there are three million cataract procedures annually in the United States, we still have a large potential to use these lenses.3
With the development of a multi-element intraocular lens (telescope), there has been a resurgence of interest in the use of these lenses for accommodative presbyopia correction. In Europe, other IOLs are being evaluated.
• Synchrony (Visiongen) is a silicone accommodating model with a two-part optic.
• Tetraflex (Lenstec) is accommodating, but with a square edge optic design to respond to cilliary muscle contractions.
• Nulens (Nulens) has a piston like design and is said to provide up to 10 diopters of accommodation as it changes shape.
• FluidVision (Power Vision) lenses are based on fluid rather than solid mechanics. Even if FDA approved significant usage, time will be needed to judge the impact of surgeon and patient preferences.
Some surgeons are implanting different lens designs in each eye. One example would be a lens pair that increases the range and depth of field in one eye to provide more acute near vision, while simultaneously addressing clear distance vision problems in the other eye with the use of a single focus implant. This technique can achieve good results, but only if the practitioner has a good understanding of the patient’s particular visual requirements and the patient accepts that there is an unknown possibility of optical change that will not be realized until after the bilateral surgery is complete and functional capacity is evaluated.
While scleral expansion surgical techniques evolve, many previously unhappy refractive surgeons are looking toward the more elegant cornea and intraocular lens solutions. Keep in mind, however, that the truly multifocal contact lens has not yet surfaced—the cornea continues to defy attempts to create simultaneous distance and near imaging.
Cornea inlays have become more feasible with the development of precise laser technology enabling facile lamellar placement. A recent improvement allows the laser to alter the structure of the inlays, potentially allowing for secondary optical/refractive changes. Here is a list of some available corneal inlays:
• The Presbylens (ReVision Optics) is a hydrogel corneal inlay with a 2mm or less diameter, to be directly implanted on the center of the cornea. This procedure is appealing because it requires a very small incision close to the visual axis. However, the closer to the visual axis, the higher the potential for complications, such as reduced best corrected distance acuity. Presbylens is currently approved for use in euro zone common market European countries. It is not yet approved for use in the United States.
• The Flexivue (Presbia) cornea inlay is similar in concept to the hydrogel Presbylens, with a larger 3mm diameter. It too is an intralamellar insertion but the lens is supplied with a patented single use implantation device. It is approved for use in Brazil.
• Kamra (Bausch + Lomb) lens is an intralamellar inlay, with a 4mm large diameter, that uses pinhole technology to increase depth of focus without altering the cornea curvature. It uses multiple laser-created microfenestrations, much the same as a keratoprosthesis back plate, which enables the facile passage of nutrient material. The Kamra is in clinical trails and not yet approved.
The patient’s pupil size is the key factor in deciding which particular model should be implanted. Inlay design, refractive index and biocompatability of the materials are all additional factors that should be considered. The inlays may be inserted in a corneal pocket or following a LASIK-type flap procedure. The target population is much younger than those commonly fitted with multifocal IOLs; the best candidates are generally early presbyopes, 40 to 50 years of age, and in need of an easily reversible procedure.
IntraCor is a femtosecond intra-lamellar laser procedure that creates concentric rings in the stroma outside the visual axis to alter the corneal curvature without changing corneal thickness. This procedure is being developed in Columbia and Germany.
At the University of Rochester’s Flaum Eye Institute, laser-initiated alterations of the cornea refractive index without modification of curvature are being explored.
It is clearly premature to speculate which of these new technological approaches the medical community will adopt and which will fail to achieve satisfactory results. Patients need to rely on the advice of their physicians and recognize that no procedure will satisfy every patient. Today’s surgeons should become involved in evaluating the various techniques while maintaining a high level skepticism to sort through the numerous claims of excellence and superiority. It’s simple: One size will not fit all.
Dr. Aquavella established the cornea
research laboratory at the University of Rochester and directed the
cornea research and fellowship training programs for 25 years. He is
currently a professor of ophthalmology at the University of Rochester
Flaum Eye Institute.
1. Baumeister M, Kohnen T. Accomodation and presbyopia: part 1: physiology of accommodation and development of presbyopia. Ophthalmologe. 2008 Jun;105(6):597-608.
2. Schachar RA. The mechanism of accommodation and presbyopia. Int. Ophthalmol Clin. 2006 Summer;46(3):39-61.
3. Congdon N, Vingerling JR, Klein BE, et al. Prevalence of cataract and pseudophakia/aphakia among adults in the United States. Arch Ophthalmol. 2004 Apr;122:487-94.