Modern refractive surgery is typically performed on the cornea. In 1949, JosÈ Ignacio Barraquer, MD, of Spain, was the first to postulate reshaping the cornea to change its refractive power.1 Since then, ophthalmologists have tested the effectiveness of different techniques to reshape the cornea, including freezing and nonfreezing keratomileusis, epikeratophakia, and radial keratotomy. With the advent of excimer laser corneal surgery—from PRK and LASIK to newer advanced surface ablation techniques, such as LASEK and epi-LASIK—the dynamic of refractive surgery changed, turning it into a more predictable, safer procedure.
WHY PHAKIC IOLs?
Although safe and reliable, laser corneal surgery has limitations.2 First, ablation of corneal tissue must be monitored. Since the advent of reports of corneal ectasia after LASIK, we have set a minimum residual stromal bed requirement of at least 250 µm. Second, laser corneal surgery not only changes the thickness of the cornea, but it also flattens or steepens the corneal curvature, resulting in myopia or hyperopia, respectively. Studies have shown that if the final corneal curvature is lower than 34.00 D or higher than 47.00 D, contrast sensitivity significantly decreases and lines of BCVA are lost. Third, ectatic diseases of the cornea (eg, keratoconus, pellucid marginal degeneration), often associated with myopia and astigmatism, are a contraindication for laser corneal surgery—even in their fruste stages.
When corneal surgery is not indicated, we must consider an intraocular procedure. With the aid of accurate biometry, modern phacoemulsification, and new IOL designs, modern lens surgery corrects ametropia with high precision and safety. The only drawback of choosing lens surgery as the primary method of refractive correction is that it destroys natural accommodation. Current accommodating or multifocal IOLs do not match the normal accommodation of young patients; however, phakic IOLs are ideal for correcting high ametropia. Phakic IOLs are predictable, stable (independent of tissue healing), and usually associated with an increase in BCVA because they do not change the natural refractive structures of the eye, such as the cornea and the lens.
For these reasons, phakic IOLs should be incorporated into any refractive surgery practice. These IOLs may significantly increase your refractive IOL volume.
WHEN SHOULD I USE PHAKIC IOLs?
In my practice, I implant phakic IOLs in the following situations: (1) myopia with a spherical equivalent greater than -7.00 D, (2) hyperopia with a spherical equivalent greater than 4.00 D, (3) lower amounts of myopia or hyperopia when the central cornea is thinner than 500 µm or the expected final keratometry reading is either less than 34.00 D or greater than 47.00 D, or (4) in all cases where there is the slightest possibility of ectasia.
Any refractive procedure requires that the patient have stable refraction for at least 18 months before surgery and be between the ages of 18 and 45 years. Although some studies show promising results in anisometropia in children, phakic IOL implantation is not normally performed in patients younger than 18 years of age. Additionally, refractive lens exchange is a better option for patients older than 45 years of age, especially in patients with myopia, because of declining accommodation and eventual onset of cataract. If glaucoma is present, it must be controlled prior to surgery. Diabetes is not necessarily a contraindication; however, a phakic IOL should not be implanted in a patient with retinopathy. Any history of intraocular inflammation is an absolute contraindication. Although ectatic disorders of the cornea are a contraindication for corneal laser surgery, they are not for phakic IOLs.
The anatomy of the anterior chamber (Figure 1A) must be considered when implanting an IOL. The minimum depth for safe implantation is 2.8 mm from the endothelium to the anterior surface of the lens. The Orbscan (Bausch & Lomb, Rochester, New York), Pentacam (Oculus Optikger‰te GmbH, Wetzlar, Germany), or an anterior chamber optical coherence tomography (OCT) device may be used to measure the anterior chamber depth. Avoid using common ultrasound biometry because it includes corneal thickness within the measurement. In the case of a thick cornea, a shallow anterior chamber may be masked.
Iris shape is also important. A flat iris is good for implantation; however, a convex iris may lead to serious complications (Figure 1B), including posterior synechie or pigmentary glaucoma.
Pupil size must also to be taken into consideration. A general rule is to keep the mesopic pupil diameter smaller than the optic diameter of the IOL.3 The corneal endothelium must also be healthy when implanting a phakic IOL. Table 1 indicates the minimum endothelial cell count according to age. Furthermore, look for good hexagonality of the cells and avoid eyes with high rates of polymegathism and pleomorphism.
WHICH PHAKIC IOL?
There are three types of phakic IOL, each distinguished by its location inside the eye. As previously mentioned, all phakic IOLs provide accurate refractive results. Therefore, the key to choosing the correct phakic IOL is in its safety profile and associated complications.
Angle-supported anterior chamber phakic IOLs. Angle-supported phakic IOLs that are fixed in the anterior chamber angle have been associated with high complication rates,4 including pupil distortion (Figure 2), iris atrophy, and endothelial decomposition. The underlying reason that complication rates are high is that placement of an angle-supported anterior chamber phakic IOL is dependent on the precise size of the anterior chamber. Currently, we do not have an accurate method of measuring the anterior chamber.
Many angle-supported phakic IOLs are no longer available. Previously, surgeons could use PMMA models, including the ZB and ZB5M (Domilens, Lyon, France) and the NuVita (Bausch & Lomb), or foldable models, such as the Vivarte (IOLTech/Carl Zeiss Meditec AG, Jena, Germany), Icare (Corneal Laboratories, La Rochelle, France), and Duet (Tekia, Irvine, California). A new angle-supported phakic IOL, the AcrySof Phakic (Alcon Laboratories, Inc., Fort Worth, Texas) should be available in Europe by the end of 2008. Clinical trials are currently under way; initial results are promising.
Iris-supported anterior chamber phakic IOLs. Jan G.F. Worst, MD, of the Netherlands, designed the first IOL in this second subgroup of phakic IOLs (Table 2). Fixed to the mid-periphery of the iris, iris-supported phakic IOLs are independent of anterior chamber size. This one-size-fits-all approach is advantageous because most complications associated with phakic IOLs stem from incorrect sizing. Iris-supported phakic IOLs are the only subtype that always centers with the pupil, reducing the phenomena of glare and halos. Although there are complications, including decentration, luxation of the IOL, and intraocular inflammation, most are related to poor surgical technique (eg, insufficient amount of grasped iris tissue, excessive manipulation) and not to the IOLs themselves.5,6
Artisan IOLs (Ophtec, Groningen, Netherlands), although safe to use, require a large incision, rendering suture closure mandatory. These IOLs may also induce astigmatism and delay visual recovery. The Artiflex (Ophtec) avoids these problems. At this time, it is my preferred phakic IOL (Figure 3).
Posterior chamber phakic IOLs. Placed between the iris and the natural lens, the most common posterior-chamber phakic IOL is the Visian ICL (Implantable Collamer Lens; STAAR Surgical, Monrovia, California). This plate-haptic, Collamer IOL is available for the treatment of myopia or hyperopia. It is also available in a toric model (T-ICL).
The ICL sits on the ciliary sulcus, so the size of the implant must fit perfectly within the sulcus, defining the ICL's vault (Figure 4A). If the ICL is short, it sits on the crystalline lens, leading to anterior subcapsular cataract (Figure 4B). If it is too long, excessive vaulting will push the iris forward and eventually close the angle. In recent years, the rate of cataracts has been lower due mainly to better sizing devices.4
Another posterior chamber phakic IOL also available for myopia and hyperopia is the silicone PRL (Phakic Refractive Lens; IOLTech/Carl Zeiss Meditec AG, Jena, Germany). This model is not as size-dependent as the ICL because it floats in the aqueous humor instead of sitting on the sulcus. The PRL is less associated with less cataracts, but its design may damage the zonula, leading to IOL migration into the vitreous.
CONCLUSION
Phakic IOLs are an indispensable tool in a complete refractive practice. If you are trying to build your premium IOL practice, I would consider adding phakic IOLs for the success of your endeavor. Phakic IOLs offer cataract surgeons a natural entry into the refractive market because it calls upon their already developed skill set. Their main indication is refractive surgery beyond the safety limits of laser corneal surgery. Patients should be below the age of 45 years. All phakic IOLs provide good refractive results; however, we must be aware of the associated complications when choosing the best phakic IOL for each case.
António A.P. Marinho, MD, PhD, is the Chairman of the Department of Ophthalmology, Hospital Arrábida, Porto, Portugal. Dr. Marinho states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +35 1936093345; marin@mail.telepac.pt.
