However, while these lenses offer several advantages over corneal re­fractive surgery, they are also associated with both potential intraoperative and long-term complications.

“The concerns with these lenses center on two issues,” says John A. Vukich, MD, assistant clinical professor at the University of Wisconsin, Madison. “First is potential corneal instability or the loss of endothelial cells over the lifetime of a patient. Second is the effect of the IOL over the lifetime on the natural crystalline lens within the eye. There is concern that placement of a phakic IOL may potentiate or hasten the development of lens opacities or cataracts.”

Another disadvantage of phakic IOLs is that the surgery is performed unilaterally, so two procedures are re­quired, making it less convenient for patients than LASIK. Additionally, the procedure takes place inside the eye. “However, you could argue whether or not it is more invasive to make an incision in the cornea and remove a controlled amount of tissue or to add an element to the eye without removing anything,” Dr. Vukich says.

There are two locations for placement of phakic IOLs. One type is placed in the anterior chamber, while the other type is placed in the posterior chamber. Each type of lens has a slightly different complication profile.

 

Figure 1. The Verisyse phakic intraocular lens from Advanced Medical Optics. Elizabeth A. Davis, MD

Anterior, Posterior Chamber Lenses

The Verisyse phakic IOL (Ad­vanced Medical Optics) is an anterior chamber lens that was approved by the Food and Drug Administration last year, and it is the only phakic IOL to date that has received FDA ap­proval. It is a one-piece, compression-molded PMMA lens that has an overall length of 8.5 mm and an optic diameter of either 5 or 6 mm. It is available in powers of -3 to -23.5 D.

The Visian Toric ICL (Staar Sur­gical) is a posterior chamber IOL that has received an approvable letter from the FDA and is expected to receive approval later this year. This is a single-piece lens design with a central concave or convex optical zone diameter of 4.85 to 5.5 mm. The lens is made of a proprietary, biocompatible, UV-absorbing, porcine col­la­gen/­Po­ly­HEMA co-polymer. It is available for my­opia -6 to -23 D with +1 to +6 D of cy­linder in 0.5-D increments.

The AcrySof angle-supported phakic refractive IOL (Alcon) is currently in Phase II trials. It is a foldable IOL de­signed for implantation into the an­te­rior chamber angle. It is a single-piece IOL with either a 5.5 mm or 6 mm diameter meniscus optic with an over­all length of 12.5 to 14 mm and a di­optric range of -6 to -16.5 D in 0.5-D increments.

Many other versions of anterior and posterior chamber implants have been used outside the United States or as part of FDA clinical trials in the United States.

AC Phakic IOL Complications

Anterior chamber lenses are either angle-fixated (AcrySof) or iris-fixated (Verisyse). The Verisyse lens requires a large incision for implantation, which can induce astigmatism and create the potential for wound dehiscence if the patient sustains blunt trauma to the eye. Additionally, the large incision typically requires be­tween three and six sutures, which delays visual rehabilitation. All large incisions have the potential for wound leaks and infection.

“It is always possible that patients with anterior chamber phakic IOLs could develop iritis, pigment dispersion syndrome, glaucoma, or persistent elevated intraocular pressure after surgery,” says Elizabeth A. Davis, MD, an assistant clinical professor at the University of Minnesota and in private practice in Minneapolis.

“One of the real advantages of the anterior chamber phakic IOLs over the posterior chamber lenses is the low incidence of cataract formation. However, a potential concern is the long-term health of the corneal en­dothelium,” says Edward E. Manche, MD, director of cornea and refractive surgery at Stanford Uni­versity School of Medicine, Palo Alto, Calif.

Figure 2. The injection technique for the Visian Toric ICL from Staar Surgical. John A. Vukich, MD

“Careful measurements of the depth of the anterior chamber are needed to make sure that there is adequate clearance between the edge of the implant and the endothelium,” Dr. Davis says.

Patients who have undergone phakic IOL implantation have not been followed long enough to determine the exact rate of endothelial cell loss. “We are following these patients with serial yearly endothelial cell counts, and if we were to notice a faster than average drop-off, we would probably remove the implant,” Dr. Davis adds.

Drs. Manche and Davis note that ophthalmologists must overcome a challenging learning curve to place the Verisyse lens. “Surgeons must en­clavate the haptics to the iris, and some ambidexterity is needed for this,” Dr. Davis says. The left hand is used to enclavate the left haptic, and then the surgeon must switch hands to enclavate the right haptic. Ad­di­tion­ally, because of the large incision, there can be a shallowing of the chamber during this step.

After surgery, there have been re­ports of iris-fixated lenses dislocating with trauma. “In fact, some lenses have spontaneously dislocated,” she says. “This is probably due to inadequate fixation, so surgeons must ensure that enough iris tissue has been brought up through the haptic.” Fortunately, these lenses are readily repositioned.

In comparison, angle-fixated lenses, unlike iris-fixated lenses, have been associated with progressive pupil distortion, synechiae formation and glaucoma, Dr. Davis says.

“Unique potential complications of angle-fixated implants could occur when the implant rides up higher in the angle than you desire,” says David R. Hardten, MD, director of refractive surgery at Minnesota Eye Con­sult­ants in Minneapolis. “In these cases, it can cause irritation and loss of the endothelial cells.”

With angle-fixated lenses that have higher compression forces, such as those made from PMMA, there is also the long-term potential for elevated intraocular pressure, says W. Andrew Maxwell, MD, PhD, in private practice at the California Eye Institute, in Fresno. Additionally, pupil ovalization can occur with angle-fixated lenses, which is cosmetically unacceptable. The pupil can become oval over time, which lets in more light and increases the potential for glare.

According to Dr. Manche, the Ve­ri­syse lens is limited to a scotopic pupil size of less than 6 mm. Patients with larger pupils can experience night vision problems such as haloes or distortion of vision related to edge glare from the lens.

PC Phakic IOL Complications

While these lenses are not associated with as much endothelial loss as anterior chamber phakic IOLs, they sit between the iris and the crystalline lens, which increases the risk of cat­a­ract formation, Dr. Manche says.

The Visian Toric ICL is a foldable lens that is implanted through an in­ject­or. The lens is injected through a clear corneal incision, similar to cat­a­ract sur­gery. So the learning curve with this technique may be less challenging. How­ever, lens implantation must be per­formed carefully so that the ICL does not touch the natural crystalline lens when it unrolls, which could induce a cataract.

The small, self-sealing incision also lowers the chance of induced astigmatism. “The ICL is thin and flexible, and there are advantages and disadvantages to that. An advantage is that it can be injected through a small incision, and if it needs to be removed, it can easily be pulled out through a very small incision,” Dr. Davis says. On the other hand, if it is not loaded into the injector correctly, it can come out sideways or upside down, which can cause it to strike the crystalline lens.

There is also the potential for cat­a­ract formation over time. “The implant could potentially touch the natural lens post­operatively and in­duce a cataract,” Dr. Hardten says. “For­tunately, this is a manageable complication. The surgeon would re­move the phakic IOL and then perform cataract surgery.”

“If there is too little vaulting, a cat­a­ract can be induced. If there is too much vaulting, then dispersion of the pigment from the iris can occur, which could raise the pressure in the eye,” he adds. Dislocation is a reported, yet rare complication with this type of lens.

Other Complications

Two complications that could occur with all phakic IOLs are anesthesia-re­lat­ed complications and endophthal­mitis. “The most feared risk with any type of intraocular surgery is end­oph­thal­mitis. In theory, one could develop an endophthalmitis that could lead to com­plete loss of vision,” Dr. Manche says.

“Because this is a totally elective procedure, we really have to be careful that we do everything we can to avoid end­ophthalmitis,” Dr. Maxwell adds.

Figure 3. The footplates of the ICL are positioned posterior to the iris following injection into the anterior chamber. John A. Vukich, MD

Another potential complication of all IOLs is dislocation, and this can occur at any time. Recently, two case reports were published describing late spontaneous dislocation of iris-claw intraocular lenses. In one case, the IOL dislocated 17 years after surgery.1

Study Results

Several studies have reported the incidence of complications with phakic IOLs. Clinical studies involving the AcrySof phakic IOL are ongoing in both the United States and Europe. Sixty patients were included in the U.S. Phase I and Phase II studies, and 70 patients were included in the European Phase II study. Primary safety endpoints included endothelial cell density counts and maintenance of best spectacle-corrected visual acuity. Acute losses in endothelial cell density related to surgical trauma were 1 percent centrally and 4.5 percent peripherally, when calculated six months post­op in the U.S. Phase I study. Clin­ical outcomes in that study showed minimal endothelial cell loss and no incidences of persistently raised IOP, pu­pil­lary ovalization or block, lens-related cataract formation, or sig­nificant dislocation of the phakic IOL.2

In the FDA study of the Verisyse lens, 1,179 eyes were included. Re­frac­tive stability was maintained out to three years. In this study, 41 eyes experienced an adverse event that was reported at 12 months after the procedure: one patient experienced hyphema; five had IOL dislocation; four had a retinal detachment; three had iritis; and 28 required surgical re­intervention. The three-year data from the clinical study indicate a continual steady loss of endothelial cells of 1.8 percent per year, and this rate has not been established as safe. If endothelial cell loss continues at this rate, 39 percent of patients are expected to lose 50 percent of their corneal endothelial cells within 25 years of implantation. The long-term effect on the cornea’s health of a 50 percent loss in corneal endothelial cells is unknown.3

According to Dr. Vukich, almost 200 eyes have undergone implantation of the Visian Toric ICL at seven U.S. clinical sites. Adverse events have included one retinal detachment and two ICL removals. The explantation of the ICLs was not due to poor vision or complications. Additionally, there have been no required repositionings of the Visian Toric ICLs due to errors in axis and no infections or clinically significant persistent elevations in IOP. 

1. Singhal S, Sridhar MS. Late spontaneous dislocation (disenclavation) of iris-claw intraocular lenses. J Cataract Refract Surg 2005;31(7):1441-1443.

2. Maxwell WA. US clinical results of the angle-supported AcrySof phakic refractive IOL. Paper presented at the ASCRS 2004 annual meeting; May 2, 2004, San Diego, Calif.

3. US FDA’s Center for Devices and Radiological Health page. Artisan (Model 206 and 204) Phakic Intraocular Lens (PIOL), Verisyse (VRSM5US and VRSM6US) Phakic Intraocular Lens (PIOL) – P030028. Available at www.fda.gov/cdrh/pdf3/p030028b.pdf.