The goal of cataract surgery in the 1990s was to restore diminished vision, exchanging a cloudy crystalline lens for an IOL. But in the past decade, cataract surgery has been slowly converted into a refractive surgery hybrid. Today, the goal of cataract surgery is achieving not only restoration of vision but also a precise refractive outcome. Every cataract surgeon wants to make the patient less reliant on glasses or contact lenses, even after routine phaco. That is why surgeons spend so much time educating and advising patients regarding the choice of an appropriate IOL.
Phakic lenses are a logical evolution from cataract replacement IOL technologies. These implantable lenses fill the gap between existing and emerging treatment modalities for spherical visual acuity defects. They are indicated for any level of myopia or hyperopia, including correction greater than 3.00 D. In 1990, several companies began to manufacture phakic IOLs, with associated instruments and devices following behind.1-3 More than 20 years later, follow- up shows excellent refractive results and vast benefits for the most difficult group of refractive patients—those with high levels of ametropia.4
PHAKIC LENS DESIGNS
There are two main differences in available phakic IOL models: placement of the implant within the eye and the materials used for manufacturing.5
Placement. Phakic lenses are designed to be implanted either in the anterior chamber or the posterior chamber. 6 Anterior chamber phakic IOLs have either anglefixated or iris-fixated designs. Posterior chamber lenses come in three designs; they can be fixated in the sulcus or on the zonular fibers or can be left free to float over the clear crystalline lens.
The ideal position for phakic IOLs is still under debate, and we are still unsure which is safest. We do know that complications can occur when any of these IOLs is placed in the wrong position. For instance, angle-fixated phakic IOLs may cause endothelial cell loss and corneal decompensation when there is little space between the body of the implant and the corneal endothelium. Iris-fixated IOLs, especially earlier models, were associated with pupil ovalization. Posterior chamber phakic IOLs have been associated with a high rate of cataract formation due to contact between the implant and the anterior capsule of the natural lens.12,13
Material. Lens material plays an important role in the safety of these implants. Polymethyl methacrylate (PMMA) has been used for a number of anterior chamber phakic IOL models, including the Baikoff ZB5MF (Morcher GmbH, Stuttgart, Germany), the Phakic 6 Model 130 (Ophthalmic Innovations International Inc.; now Aaren Scientific Inc., Ontario, California), the NuVita Baikoff MA 20 (Bausch + Lomb, Rochester, New York), and the iris-fixated Artisan (Ophtec GmbH, Groningen, Netherlands). When these rigid lenses are implanted in the anterior chamber, they require large incision sizes (over 6.0 mm) and suture closing, which can lead to induced astigmatism. Foldable materials have been used for some anterior chamber phakic IOLs, including hydrophobic acrylic for the AcrySof Cachet angle-supported lens (Alcon Laboratories Inc., Fort Worth, Texas) and silicone for the iris-supported Artiflex (Ophtec GmbH).
Foldable materials are also used in all posterior chamber phakic IOLs, including Collamer in the Visian ICL (STAAR Surgical, Monrovia, California) and silicone in the PRL (IOLTech/Carl Zeiss Meditec, Jena, Germany; Figure 1). These materials allow the lens to be implanted through smaller incisions (2.5-3.0 mm) and avoid the need for suturing.14-16
Biocompatibility is also important for phakic IOL materials. These lenses must not cause chronic inflammation, cataract formation, or progressive endothelial cell loss— side effects that were seen with earlier phakic IOL models. Additionally, materials with a higher refractive index are preferable because they produce thinner implants. Thin posterior chamber phakic IOLs have many advantages compared with thicker implants, including an easier implantation procedure and fewer complications… read more