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PHAKIC IMPLANTS

For patients who are not good Lasik candidates, for reasons that range from having too high a prescription, having corneas that are too thin, to abnormal corneal curvature, the phakic implant technology may be an option for reducing spectacle dependence.  This technology involves inserting an artificial lens into the eye, to correct a person’s prescription.  Some people have referred to this as the intraocular contact lens, but it is not contact lens in the ordinary sense of the word.  This lens is left “permanently” inside the eye, positioned in one of three locations: 1) angle-fixation: inside the anterior or front chamber, held in place by the haptics or the “feet” of the implant positioned in the angle of the eye; 2) iris-fixation: inside the anterior chamber, held by attachments of the haptics of the implant to the iris, the colored part of the eye; and 3) behind the iris and pupl and in front of the natural crystalline lens. (see Tour of Eye)

There are currently two phakic implants that have been approved in the U.S., the Verisyse phakic IOL and the Visian ICL phakic implant. The Verisyse is an iris-fixated phakic implant. It is attached to the front of the iris with tiny claws. It has been approved for the reduction or elimination of nearsightedness in adults aged 21 and over, with nearsightedness ranging from –5 to –20 diopters. The currently approved model has to be inserted through a large incision, and does not correct astigmatism. Other versions in the works include a foldable model which can be inserted through a small, no-stitch incision, and one that corrects astigmatism.

The other phakic implant, the Visian ICL or implantable collamer lens, has also been FDA approved.  This lens is placed behind the iris and in front of the natural lens of the eye.  It is approved for reduction or elimination of nearsightedness in adults aged 21-45 years, with nearsightedness ranging from -3 to -20 diopters, and less than or equal to 2.5 diopters of astigmatism.  A version of the Visian ICL to correct astigmatism is in the final approval process.  Unlike the current U.S. Verisyse model, the Visian ICL can be inserted through a small, no-stitch incision, which is arguably safer and results in faster visual rehabilitation.

With either type of phakic implant, for patients who have a significant amount of astigmatism, this can be treated in one of two ways: 1) limbal relaxing incisions or astigmatic keratotomy—incisions made in the cornea to relax the astigmatism; or 2) Lasik, Epi-Lasik, or PRK, if the patient is a candidate for these. Some patients may not be candidates to have full correction of their nearsightedness with Lasik, but may be able to have a small residual prescription including astigmatism, treated. So for patients who have a lot of astigmatism, reduced dependence or elimination of glasses may involve a two-stage procedure, first phakic implant surgery, then surgical reduction of astigmatism.

There is no question that the phakic implants work well to correct a full range of prescriptions. The main issue is now safety. Studies have shown that there is a continual and steady loss of endothelial cells. These cells line the back part of the cornea, and function to keep the cornea clear of fluid. They can be thought of as miniature “sump pumps”, which pump fluid out of the cornea to keep it crystal clear. If too many of these cells are lost, the cornea can become swollen, lose its clarity, and cause decreased vision. While this may not be a concern for older patients, the question is whether this will cause a long-term problem for younger patients who receive and live with the implants for a longer period of time. Since these phakic implants involve more invasive surgery, there are additional risks as well, including cataract formation. If a cataract develops, the phakic implant can be removed, and standard cataract surgery can be performed to restore vision. In all likelihood, this technology will become very important for the under-40 set. Currently, these phakic implants do not compensate for the loss of near vision (accommodation) that occurs in the over-40-years-old set, so glasses for reading need to be worn for these patients. These implants are the best hope for patients whose nearsightedness is greater than –8.00 diopters, and certainly greater than –12.00.

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