In the 1950s, José Ignacio Barraquer, MD, of Spain; Benedetto Strampelli, MD, of Italy; M. Dannheim, MD, of Germany; and D. Peter Choyce, MD, FRCOphth, of London—the pioneers of intraocular implants—conducted the first trials using anterior chamber refractive lenses to correct high myopia in phakic eyes. Unfortunately, the initial experiments revealed unacceptable complication rates due to imperfections in IOL design.1 Glaucoma, corneal dystrophy, and hyphema were commonly observed, and anterior chamber implants—particularly refractive phakic implants—acquired a bad reputation.
EARLY PROTOTYPES
It was not until the mid-1980s when Svyatoslav N. Fyodorov, MD, of Moscow; Paul U. Fechner, MD, of Germany; and I resumed developing phakic implants.
Dr. Fyodorov began experimenting with a collar-button, pupil-fixated posterior chamber implant that ultimately led to the development of the Implantable Contact Lens (ICL; STAAR Surgical Company, Monrovia, California), the Adatomed implant (Chiron Adatomed GmbH, Ratingen, Germany), and the Phakic Refractive Lens (PRL; Ciba Vision, Duluth, Georgia). Dr. Fechner designed the Worst iris claw implant (Ophtec BV, Groningen, Netherlands) and adapted it to correct high myopia. Later, Ophtec BV modified the implant to correct hyperopia and astigmatism.
I imagined an angle-supported implant to correct myopia similar to that designed by Charles D. Kelman, MD, of New York. Over the last decade, the development of phakic implants has been erratic: first one type met with success, then another. In fact, the progress of these lenses was largely hindered by the importance of concurrent investment and research into corneal surgery, microkeratomes, and the excimer laser. Because LASIK developed so rapidly, today, its advantages and limitations are much better known. Due to the procedure's drawbacks, interest and research in refractive implants are once again gaining momentum.
AVANTAGES OF REFRACTIVE IMPLANTS
Ease of use. The use of viscous solutions and soft implants has simplified surgery. All anterior segment surgeons are able to perform corneal surgeries without specialized training and with a minimal investment in technology. The accuracy of refractive implants in restoring vision is an acknowledged fact, and, for high ametropia, implantation is generally a better option than LASIK and demonstrates excellent predictability.
Fewer complications. Apart from progressive myopia and cataract development, the stability of refractive results has been confirmed regardless of the implant type. Safety and efficacy ratios are superior to those obtained with LASIK, and optical aberrations are fewer.2,3 In most instances of high ametropia, the effective optical zone is larger, and the rate of nighttime halos is lower for employing refractive implantation versus corneal surgery. Additionally, fewer optical defects occur with industrial lens implantation compared with corneal surgery, because the ultimate shape of the corneal tissue depends on the individual's healing ability.
In most cases, refractive implant procedures are reversible. In the event of a sizing or power error, the lenses can be exchanged. In the future, they may even be adaptable, either with light-adjustable technology, as seen in the Light Adjustable Lens (LAL; Calhoun Vision, Inc., Pasadena, California) or combined with a bioptic.
DISADVANTAGES OF REFRACTIVE IMPLANTS
The disadvantages of refractive implants depend on the lens model and its anatomical situation. Each new modification can induce an unexpected iatrogenous complication.
Angle-supported anterior chamber implants. Respecting a safety profile has eliminated the early endothelial trauma observed with the first models. To prevent endothelial loss, there must be a minimum of 1.5 mm between the edges of the optic and the endothelium. More than 80% of the first-generation (years, 1988-1989) ZB-type Baikoff phakic IOL implants have been extracted. Since 1990, and only until last year, no known or published corneal dystrophy epidemic has been reported with new-generation implants.
Indeed, sudden drops in endothelial cells have been described in France, when the Vivarte or Newlife lens (both manufactured by Carl Zeiss/IOLTech, La Rochelle, France) was implanted in patients 4 or 5 years ago. During the first 3 or 4 years, the endothelial cell loss is physiological. A sudden drop in the number of endothelial cells occurred after the fourth year and led to explantations in 10% to 20% of cases. These implants were withdrawn from the market and a warning issued—not only with regard to these implants, but to all types of anterior chamber implants.
In our experience, we have noted that second-generation PMMA implants (ZB5M [Domilens GmbH, Hamburg, Germany] or Nuvita [Bausch & Lomb, Rochester, New York]) presented few endothelial problems, and the average number of years before it was explanted (for whatever reason) was approximately 11 years. It was only 2 years with the Vivarte and Newlife. We were unable to find anatomical reasoning for the endothelial cell loss. Moreover, there did not seem to be any relationship between the anterior chamber depth and endothelial cell loss. We, therefore, wondered if it was a question of hydrophilic polymer tolerance in the anterior chamber.
Likewise, the risk of cataract formation, ocular hypertonia, or induced uveitis is low. There remains the partially unresolved problem concerning the possibility of pupillary ovalization, however. Most cases have occurred due to an oversized implant, although some clinicians have observed the phenomenon with perfectly sized implants secondary to footplate irritation in the angle.
The future of angle-supported implants lies in perfecting the preoperative evaluation of the anterior chamber's internal diameter. Anterior chamber implants have followed the example of posterior chamber implants and may now be inserted through a 3-mm or smaller self-sealing incision. Today, all of the modern angle-supported implants are developed in this way.
Iris claw/iris-fixated implants. The main advantage of these lenses is their independence concerning the diameter of the anterior chamber. Only rigid PMMA implants requiring a 5.5- or 6.0-mm incision are Conformité Europeéne (CE) marked. Pinching the implant at the iris requires a certain amount of expertise, and less skillful surgeons may slightly decenter the implant.
The complication rate of iris-fixated phakic IOLs has fallen. Endothelial cell loss is acceptable, and inflammation, pupillary blocks, and IOL displacements are rare. A few implant dislocations were observed when the IOL was not firmly fixed at the iris.2,3 Pigment dispersion has been noted in hyperopes,2,3 and I observed several cases—essentially in hyperopes and in one case in a myope—when I carried out a retrospective analysis of the anterior chamber on several hundred patients using the Visante OCT (Carl Zeiss Meditec AG, Jena, Germany). We were able to show that pigment dispersion always occurred when the crystalline lens rise was equal to or greater than 600 µm.1-6 The forward protrusion of the crystalline lens pushes the iris toward the front, creating a sandwich effect where the iris is squashed between the implant and the crystalline lens. At that moment, pigment dispersion syndrome occurs.
Therefore, we no longer offer iris-claw implants to patients if their crystalline lens height/rise is more than 300 µm. By keeping to this rule, we have been able to eradicate this problem from our practice. It is important to note, however, that the crystalline lens' anterior pole moves forward by 20 µm per year. From 10 to 15 years on, we will once again be confronted with this problem.
We were also able to demonstrate that corneal dystrophy could appear in myopic patients if the internal diameter of the anterior chamber was small (ie, approximately 11 mm). For the time being, there is no risk of corneal endothelial dystrophy in eyes with normal diameters.
To solve the large incision problem, a foldable version of the Artisan lens (Ophtec BV; marketed in the US as the Verisyse IOL by Advanced Medical Optics, Inc., Santa Ana, California) (Figure 1), called the Artiflex implant, is being developed by Ophtec BV.
Posterior chamber implants. Apart from an ineffective attempt with large-diameter posterior chamber PMMA implants, all posterior chamber lenses now in use are foldable for insertion through a 3-mm incision. Chiron Adatomed GmbH (Ratingen, Germany) has completely abandoned the implant it was developing because of the high incidence of induced cataract formation.
Currently, surgeons prefer either the ICL or the PRL. The risk of cataract formation is still a problem, especially regarding the ICL. The rate increases with age and insufficient vaulting of the implant.4 Additionally, cases of unexplained intravitreous dislocations with the PRL have been recently published (oral communication with Dimitri Dementiev, MD, at the ESCRS Winter Meeting, Barcelona, Spain, February 2004). Whether this complication is due to surgical trauma, the cutting effect of the PRL's edges or a fragile zonule is unknown. This complication has not been described with the ICL, which is sulcus-fixated.
THE FUTURE OF PHAKIC IMPLANTS
Phakic implants offer the advantage of correcting all degrees of ametropia. The only concern associated with their use is the manufacturing of the optic. Today, these lenses are indicated for low-to-moderate myopia in cases of corneal abnormalities. For example, astigmatism associated with ametropia can be treated with toric lenses such as the ICL and the Artisan lens. The optical results are superior to those obtained with PRK or LASIK. Correct implant orientation is essential at the time of surgery; otherwise, visual acuity will suffer.
More recently, the correction of presbyopia has been suggested using the Vivarte or the GBR Presbyopic multifocal (both manufactured by IOLTech, La Rochelle, France) implants. The advantage of such IOLs is their reversibility, because multifocality can induce unpleasant optical side effects (eg, halos, glare, loss of contrast sensitivity, diplopia). In that case, it is theoretically easier and more practical to remove these lenses than to correct a similar problem resulting from multifocal LASIK. Unfortunately, this technique was stopped because of endothelial cell problems that were observed in France. This does not, however, put a stop to using a multifocal lens on phakic implants, but they must only be proposed with implants that have satisfactory tolerance levels.
Today, phakic IOLs represent only a small part of refractive surgery indications. However, because of their optical qualities and their theoretical and practical advantages, as well as the contraindications and limitations of LASIK, I initially believed that these implants would make up approximately 20% to 30% of the refractive surgery market. Unlike what I thought some years ago, the market of phakic implants will probably not be as important as first estimated because of the adverse effects we have observed on all types of implants. Their usage will probably only cover 10% to 20% of refractive surgery indications. Indeed, careful measuring of the anterior segment with the OCT enabled us to establish contraindications based on the internal dimensions of the anterior chamber, and in some cases, when the anatomical conditions cannot be met, some patients may not undergo LASIK or have a refractive implant.
Our experience shows that the key to successfully using angle-supported implants is evaluating the anterior chamber's internal diameter. Previously, measuring the external white-to-white measurement was imprecise. Today, however, axial imaging techniques that cover the entire diameter of the anterior segment such as the Scheimpflug technique, high-frequency ultrasonographs, and an optical coherence tomographer are in development (Figure 2). Their precision has a 50-µm variation. The software of these devices may shortly be capable of simulating the presence of an implant in the anterior segment, thus indicating whether or not the safety guidelines have been respected.
INDICATIONS FOR REFRACTIVE PHAKIC IMPLANTS IN 2007
As previously mentioned, the indications for refractive phakic implants are increasing because of the limitations and contraindications of PRK and LASIK. For example, LASIK is contraindicated for patients suffering from dry eyes because of their risk of persistent postoperative discomfort. In these cases, a refractive implant does not interfere with the production of tears. Moreover, intraocular pressure (IOP) measurements are often inaccurate after refractive photoablation. Indeed, measures are often lower by 5 to 7 mm Hg. In my personal indications, I consider glaucoma suspects with borderline IOPs to be good candidates for refractive implants, because postoperative ocular tension measurements are not disturbed, and no correction coefficient has to be applied. This indication seems legitimate, because ocular hypertonia is not induced by refractive implants, except for postoperative transitory steroid hypertonia.
Today, toric phakic implants are a means to correct early keratoconus, as inserting such an implant through a posterior corneoscleral incision does not interfere with the evolution of the cornea. On the other hand, it is important to specify that this type of surgery will not modify the evolution of the cornea, but it will offer a satisfactory optical correction for patients who show a complete intolerance to contact lenses and before they reach the stage of a corneal graft.
Approximately 18% of refractive surgery candidates have corneal abnormalities that include a cornea thinner than 500 µm, asymmetrical and irregular astigmatism, and forme fruste or true keratoconus. Additionally, there is a risk of corneal ectasia in the presence of one of these factors.
I observed a few patients who had undergone refractive photoablation on one eye and a clear lens extraction in the other. The eye that underwent corneal surgery developed ectasia, whereas abnormalities had hardly evolved in the eye that underwent intraocular surgery. Moreover, failures, insufficiencies, regressions, or overcorrections following radial keratotomy, PRK, and LASIK are excellent indications for refractive implants.
CONCLUSION
Today's situation with refractive lens implants is far superior to that of 20 years ago. The concept of this procedure has been accepted. A large number of refractive implants have obtained the CE mark, and two models received US Food and Drug Administration (FDA) approval. It is also mandatory to warn the patient, however, that because the anterior segment will undergo modifications with age, it will no doubt be necessary to remove the implant after time—between 10 and 30 years—to avoid complications.
Georges Baikoff, MD, is Director and Professor of Eye Surgery at the Ophthalmology Centre of the Monticelli Clinic, in Marseilles, France. He states that he is the inventor of the Vivarte/GBR phakic IOL. Dr. Baikoff may be reached at +33 491 16 22 28; g.baik.opht@wanadoo.fr.
Up Front | Sep 2007
Refractive Phakic IOLs of Then and Now
Herein, I share the development of and experience with these implants.
Georges Baikoff, MD
