Phakic, accommodative, and multifocal IOLs will certainly receive attention from most anterior segment surgeons within the next 3 to 5 years. My perspective on the subject is based upon my experience as a cataract/IOL and refractive surgeon, as well as my position as President and CEO of Vision Membrane Technologies, Inc. (Carlsbad, CA), a company formed to create phakic single-vision and bifocal IOLs.
Every procedure involving the implantation of an IOL can only be as effective as that lens' function. Assuming that an IOL optic is developed that can produce excellent distance and near visual function, the question becomes in which circumstances should such products be used. From the front to the back of the eye, the major refractive surgical options will include:
1. LASIK and PRK;2. a phakic anterior chamber IOL, single-vision and multifocality;
3. a phakic iris-fixated IOL, single-vision and multifocality;
4. a phakic posterior chamber IOL, single-vision and multifocality; and
5. a pseudophakic, posterior chamber (in-the-bag) IOL, single-vision and multifocality.
Which of these surgical options is appropriate for (1) a 50-year-old refractive surgery patient, (2) a 20-year-old refractive surgery patient, or (3) a cataract patient? In Table 1, I prognosticate the surgical choices for these patients. To answer these questions, we should first consider the evolution of IOLs.
HISTORY OF SINGLE-VISION REFRACTIVE IOLSAnterior Chamber Phakic IOLs
Georges Baikoff, MD, of Marseille, France, deserves credit for designing and popularizing refractive IOLs based on a previous anterior pseudophakic lens design that uses standard refractive optics. The optic had to be reduced in size from 6.0 mm to 4.2 mm in order to provide clearance from the endothelium. This requirement frequently causes glare when the pupil dilates, because the IOL centers on the geometric center of the eye and the pupil is somewhat displaced. As a r
esult, once the pupil size approaches 3.5 to 4.0 mm, the patient commonly experiences glare.
Also of interest, Vision Membrane Technologies, Inc., has begun human implantation trials of a very thin, phakic, anterior chamber, angle-fixated IOL called the VISION MEMBRANE. As a result of diffractive optics, the optic's diameter can be expanded to 6.2 mm because the thickness of the IOL is only between 200 and 300 µm for all refractive powers (compared with a routine IOL thickness of 700 to 1,000 µm). Although centration with the lens has been excellent, the long-term risks of synechiae formation and pupil ovalization must be studied. Reversability has proven far simpler than with other refractive IOLs; several VISION MEMBRANE lenses have been removed from the anterior chamber through the original 3-mm wound.
Posterior Chamber Phakic IOLs
Svyatoslov Fyodorov, MD, of Moscow developed the concept of a phakic posterior chamber IOL, now embodied by the STAAR ICL (STAAR Surgical Company, Monrovia, CA) and the PRL (CIBA Vision, Duluth, GA). Optically, the position of this IOL type behind the pupil is ideal, but ultrasound has shown it often to be in contact with the anterior lens capsule and to change position continuously.1 As a result, many surgeons are concerned that the incidence of cataract formation will rise to unacceptable levels with time.
Iris-Fixated IOL
Jan Worst, MD, of Haren, The Netherlands, pioneered the concept of an iris-fixated IOL (the Artisan lens [OPHTEC, Gronigen, The Netherlands]; pending FDA approval, this IOL will be marketed in the US by Advanced Medical Optics, Inc. [Santa Ana, CA], as the Verisyse). Patients' quality of vision is generally excellent with the lens' 5.5-mm optic diameter, but achieving precise centration while clipping the IOL to the iris can be difficult. A foldable version of the Artisan is in development.
CORRECTING PRESBYOPIAAccommodative IOLs
Efforts to correct presbyopia have taken two different paths. The first involves an accommodative IOL, which is placed into the capsular bag after lens extraction. Examples of this IOL design include the CrystaLens (C&C Vision, Aliso Viejo, CA) and the 1CU Akkommodative IOL (HumanOptics AG, Erlangen, Germany).
At issue is the need for documentation of the true accommodation provided by such IOLs compared with the pseudoaccommodation of a routine posterior chamber IOL due to the effect of a small pupil. Can patients routinely achieve +2.00 D of accommodation for a long period of time despite capsular fibrosis?
Multifocal IOLs
The second option is implanting a static IOL that creates a multifocal effect based on its optical mechanics. Until now, the Array lens (Advanced Medical Optics, Inc.) has numerically been the most successful multifocal IOL. The Array achieves its multifocal optical effect via a series of aspheric optical patterns. Patients commonly complain of nighttime halos with the Array lens. I believe the future of multifocal IOLs lies with diffractive optics, rather than with refractive optics, to provide the near vision capability.
The MA60D3 IOL (Alcon Laboratories, Inc., Fort Worth, TX) is currently in FDA clinical trials. This lens derives its add power from diffractive optics for near vision that are superimposed onto refractive optics for distance. If optics similar to this design are used as a phakic refractive multifocal IOL, then the add required to correct presbyopia can be approximately +1.00 to +1.25 D when combined with the patient's residual accommodative ability.
PERSONAL PHILOSOPHYCataract Surgery
For a cataract patient, the surgeon removes the crystalline lens and implants either an accommodative or a diffractive multifocal IOL in the capsular bag. The visual result depends upon the efficacy of the IOL, but I have little doubt that, if it can provide patients with high-quality distance and near vision without a need for spectacles, a multifocal IOL of some type will be the lens of choice in the future.
Keratorefractive Surgery
The advantage of using an IOL for refractive purposes is that all patients have the potential to achieve the same high quality of vision. Patients typically experience no halos when they receive a standard, monofocal IOL. The dry eye and prolonged healing times common with keratorefractive surgery are not significant issues with IOLs.
Presbyopic Correction
For the phakic refractive patient, I think it makes very little sense to remove a clear lens, eliminate available accommodation, and then implant a posterior chamber IOL. The risk of the lens extraction combines with the limited accommodation offered by the IOL. This procedure may be the only available option for presbyopic correction today, but I am focusing on the near future, when all the types of IOLs mentioned earlier are available. I must argue against minimizing the importance of removing the normal crystalline lens in a younger patient, because any complication can have a long-term, devastating effect on his lifestyle and eliminate his ability for +1.00 D to + 2.00 D of accommodation.
In such a case, I favor an additive IOL that may be explanted, is unassociated with the risks of clear lens extraction, and requires less add power than an in-the-bag, accommodative lens. I believe the best IOL design will employ diffractive optics for the add, because they substantially reduce the amount of halos and glare experienced by the patient.
FITTING LENSES TO PATIENTS
Keratorefractive and cataract surgeons must determine at which refractive power the trade-off of risks associated with IOL implantation versus efficacy is appropriate. Table 1 shows my prognostications of the surgical choices for the patients I presented at the beginning of this article. Table 2 describes the phakic refractive IOL options that I believe will be available by 2010 and their relative risks.
CONCLUSION
Let the trials begin! I am certain that phakic IOLs will play a major role in the correction of refractive error and presbyopia in the near future. The downside of this surgical option is the slight increase in surgical risks, while the upside is a truly excellent quality of vision. As always, surgeons must determine how best to balance risks and benefits for their patients.
1. Garcia-Feijoo J, Alfaro IJ, Cuina-Sardina R, et al. Ultrasound biomicroscopy examination of posterior chamber phakic intraocular lens position. Ophthalmology. 2003;110:163-172.
