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Phakic IOLs can provide accurate and stable correction of myopia, but their potential to result in serious complications remains a cause for concern. Care in selecting appropriate candidates and the implantation procedure are critical to optimize the risk:benefit ratio.
Milan-Phakic IOLs available in the United States for the treatment of myopia can provide excellent vision outcomes, but careful attention to patient selection, a thorough preoperative exam, and meticulous surgery are critical for optimizing safety, said Lucio Buratto, MD.
"Results have been favorable with both the posterior chamber implantable contact lens (Visian ICL, STAAR Surgical) and the iris-fixated phakic IOLs (Verisyse, Advanced Medical Optics) in the multicenter FDA studies," said Dr. Buratto, director of Centro Ambrosiano di Microchirurgia Oculare, Milan, Italy. "However, the rates of complications, including glaucoma, cataract formation, endothelial cell loss, and retinal detachment, are still potentially too high for a procedure being performed in a healthy eye.
"Nevertheless, refractive surgery with phakic IOLs has a positive future because surgeons can reduce those risks if they take care in selecting patients and performing the surgery and if the manufacturers work to improve the quality of the implants further," he said.
The "right" eye for phakic IOL implantation is defined by a set of anatomic characteristics. Endothelial cell count should exceed 2,000 cells/mm2 , and the anterior chamber depth, measured from the endothelium to the crystalline lens, should exceed 2.8 mm. In addition, the angle width should be larger than 30°.
The preoperative evaluation should include traditional metrics but also should incorporate more sophisticated imaging technology that can provide accurate information for selecting appropriate patients and correct IOL size. Options include anterior chamber optical coherence tomography (Visante, Carl Zeiss Meditec), very high-frequency digital ultrasound (Artemis 2, UltraLink LLC), or the Scheimpflug photography-based anterior segment imaging technology (Pentacam, Oculus).
"Those devices can provide measurements that include anterior chamber depth, angle width, the white-to-white measurement, the sulcus-to-sulcus distance, and pupillary diameter-all of which are critical for deciding whether or not to implant a phakic IOL and for choosing the correct one," Dr. Buratto said.
The imaging technologies also are useful for postoperative evaluation because they allow the surgeon to determine the exact intraocular position of the IOL; its relationship to other structures in the eye, including the crystalline lens, the iris, and the endothelium; and the patency of the full-thickness iridectomy that must be performed to prevent pupillary block.
In addition to performing a good iridectomy, important surgical elements include avoiding contact with the crystalline lens during phakic IOL implantation and thorough, careful removal of the viscoelastic after surgery.
Attention to IOL sizing also is critical when implanting the ICL.
"If the ICL is too short, it can decenter and come into contact intermittently with the crystalline lens, leading to anterior capsular cataract formation. If it is too long, it can vault excessively, leading to chronic iris chafing, pigmentary dispersion, and possibly angle-closure glaucoma," Dr. Buratto said.
When implanting the iris-fixated phakic IOL, surgeons must pay special attention to centration as well as to correct enclavation and careful iris manipulation.
"With this lens, one size fits all," Dr. Buratto said. "However, there remain risks of potential disenclavation consequent to poor enclavation at the time of surgery or iris local atrophy in the long term and risk of intermittent endothelial contact."