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Phakic IOL implantation is as potentially viable a means to correct myopia as LASIK/PRK or refractive lens exchange, said Sonia H. Yoo, MD.
San Diego-Phakic IOL implantation is as potentially viable a means to correct myopia as LASIK/PRK or refractive lens exchange, said Sonia H. Yoo, MD.
Among the advantages of phakic IOLs are they can correct high degrees of ammetropia, they preserve accommodation, and they result in fewer higher-order aberrations than other methods, she noted, speaking at World Cornea Congress.
But they’re not perfect, and they do require intraocular surgery, bringing with them all the potential risks of incisional surgery, said Dr. Yoo, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine.
Current phakic designs include iris-supported anterior chamber lenses (AMO’s Verisyse is approved in the United States, while its Artiflex is not), and angle-supported anterior chamber lenses (Alcon’s AcrySof Cachet, currently in phase III studies). STAAR Surgical’s Visian ICL is the only approved posterior chamber lens (implantation needs to be between the anterior capsule and the iris, Dr. Yoo said).
The Hole ICL and Toric ICL are not yet approved, although the latter is under FDA review.
The Hole ICL “is designed to prevent pupil block and obviates the need for peripheral iridotomy,” she said.
The Verisyse has been approved since 2004, and the FDA study results showed almost all patients had 20/40 after 3 years, but only half had an improvement in vision, and 6% had a loss of 1 or 2 lines. Complications in the FDA study ranges from a 1.8% endothelial cell loss rate per year to iritis in the early postoperative period and implant decentration.
The Visian has been approved since 2005, and surgical implantation vaults the lens over the lens capsule to minimize the risk of cataract formation.
“There are several advantages of posterior chamber phakic IOL over their anterior chamber counterparts,” she said, including smaller wounds, minimal induction of astigmatism, a similar technique to IOL implantation during phaco, and cosmetics-the lens is less visible as it’s mostly hidden behind the iris, Dr. Yoo said.
The key to a successful posterior chamber implantation is an anterior chamber depth of at least 3 mm-a shallow anterior chamber leads to endothelial cell loss and complicates the phakic IOL insertion, she said.
A recent study in American Journal of Ophthalmology cited the 8-year endothelial cell loss at 6.2%.
“Recent studies have shown a stabilization of endothelial cell loss 2 years after ICL implantation, as we learn more about the ideal patient characteristics,” Dr. Yoo said.
Ideally, the lens vault should be about 500 μm, she said, which is determined by ICL length measurement and “adding 0.5 mm to the horizontal corneal diameter.”
Some pearls for preoperative planning: “White-to-white measurement is critical,” she said.
It’s best to measure with a caliper; recline the patient under the microscope or in the exam lane.
“High-frequency ultrasound may offer improved sizing and the sulcus dimensions may be objectively measured by optical coherence tomography,” she said.
Sizing complications can lead to increased IOP (if it’s too long), to early cataract formation (if it’s too short).
There are numerous potential postoperative complications, which can range from pigment on the ICL and elevated IOP in the early postoperative period to glare and halo or decentration in the late postoperative period, Dr. Yoo warned. In rare cases pupil ovalization may occur.
The 8-year study also found 73% of 41 eyes had 20/20 uncorrected distance visual acuity (UCVA), 85.4% were within 1 D of target refraction, and most had an improvement in contrast sensitivity. An earlier 4-year study on 56 eyes of 34 patients found 95% had 20/40 or better UCVA and 70% had 20/20 or better UCVA; 93% were within 1 D of target refraction.
“Other comparative studies have shown UCVA is better in posterior chamber phakic IOLs compared with LASIK in patients with baseline myopia of –3 D to –7.88 D,” she said.
“ICL implantation results in significantly fewer ocular higher-order aberrations than wavefront-guided LASIK,” she said. “In eyes with low-to-moderate myopia, contrast sensitivity was significantly improved after ICL implantation.”
Future designs for phakic IOLs will concentrate on easier insertion/removal, easier fixation, thinner profiles to eliminate contact with adjacent tissue, and large optical zones.
“Clinicians must warn patients of the potential complications of these lenses, and I recommend patients have a retina exam before surgery,” Dr. Yoo said. “Future directions may include the ability of these lenses to treat presbyopia, hyperopia, and astigmatism.”