The Phakic Refractive Lens (PRL; CIBA Vision, Duluth, GA) has been available in Europe in both a myopic and a hyperopic model since 2001. The myopic model is currently in Phase III FDA trials in the US. The PRL is composed of a proprietary silicone elastomer that renders it gossamer-thin and exceptionally flexible and pliable. It is made of a hydrophobic material and has a refractive index of 1.46. Its curvature duplicates that of the crystalline lens. The PRL is designed to maintain an aqueous fluid layer between its posterior surface and the crystalline lens. This should aid in preserving the natural metabolism of the lens and prevent potential opacification. To our knowlege, no visually significant cataract formation has occurred after implantation of this lens.
Initially, only the myopia models PRL 100 (10.8 mm long) and PRL 101 (11.3 mm long) will be available in the US. Both models are 6.0 mm wide and have functional optical zones of 4.5 to 5.0 mm, depending on the dioptic power.
SURGICAL TECHNIQUE
We begin by fashioning two sideport incisions. Although seemingly insignificant, this step becomes crucial later in the procedure. The incisions should be generously sized, but the tunnel length must be short in order to prevent “oar lock” of the lens manipulator. We then use viscoelastic to deepen the anterior chamber before creating a clear corneal incision. In this case, we used a 2.5-mm keratome and enlarged the incision from approximately 3.5 to 3.8 mm to facilitate insertion of the IOL with forceps. The inserting Dementiev PRL forceps (CIBA Vision) features a central cavity that helps the surgeon avoid direct contact with the lens' optic.
We float the PRL onto a little BSS (Alcon Laboratories, Inc., Fort Worth, TX; and CIBA Vision in Europe) and grasp it along its longitudinal axis. The implant folds together as it passes through the clear corneal incision (Figure 1). The leading haptics tuck in or fold upon themselves, and we simply course across the anterior chamber as we remain cognizant of the anterior lens capsule and corneal endothelium. We then use a Weck cell sponge to grasp the trailing haptics so that the implant does not escape. With a small nudge, the implant is now in position to insert the leading haptic posterior to the plane of the iris (Figure 2), and we use the Dementiev PRL spatula (CIBA Vision) and viscoelastic to open or deepen the ciliary sulcus. At this point, we take care to avoid touching the anterior lens capsule. No particular lens orientation is required; we simply tuck in each haptic posterior to the iris. Once the haptics are in place, we instill a miotic agent. As the pupil constricts, we subtly adjust the implant for perfect centration. Typically, we remove the viscoelastic agent in a manual fashion and flush the anterior chamber with BSS.
FURTHER DEVELOPMENTS
Since acquiring the PRL from Medennium, Inc. (Irvine, CA), CIBA Vision has developed an injector delivery device that facilitates insertion of the IOL and may further reduce any risk of trauma to the corneal endothelium and anterior lens capsule. The injector is currently available in Europe and is the only insertion method CIBA Vision incorporates into its PRL training courses. The company is also in discussions with the FDA to incorporate the injector as part of the protocol for the US clinical trials.
Dimitrii D. Dementiev, MD, is Director of the Department of Ophthalmology in San Babila Day Hospital in Milan, Italy, as well as Medical Director of New Line Vision Eye Research Institute in Moscow, Russia. He is a consultant for CIBA Vision. Dr. Dementiev may be reached at + 39 33 56 02 56 65; dimitrii.dementev@iol.it.
