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Publication Exclusive: Phakic IOLs may make cataract surgery more challenging
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For extremely nearsighted patients who are seeking independence from glasses and contact lenses, implantation of a phakic IOL can be a reasonable choice. In the U.S., we have access to two different types of phakic IOLs: anterior chamber iris-clip phakic IOLs and posterior chamber sulcus-fixated phakic IOLs. Both of these options can correct extreme degrees of myopia, as much as –20 D, and they are both designed to stay inside the eye for many years. At some point, however, when a cataract develops, the phakic IOL will need to be explanted at the same time as the cataract surgery. Then a single in-the-bag pseudophakic IOL can be implanted to address the refractive state of the eye. This is more complicated than a standard cataract surgery, and care must be taken at every step in order to achieve the best visual outcome.
Posterior chamber phakic IOLs
These thin and flexible phakic IOLs are placed in the posterior chamber and wedged into the ciliary sulcus for stability. The incision from the phakic IOL surgery is typically 3 mm wide or smaller and made in the limbus or cornea. The cataract change can be age-related and unrelated to the phakic IOL, or it can be a direct result of the phakic IOL touching the anterior lens capsule of the crystalline lens, thereby inducing cataractous changes. As the cataract opacity progresses, there can be enlargement of the lens, particularly in the anterior-posterior dimension. This will lead to less space for the phakic IOL and could lead to touch of the anterior lens capsule.
When examining the patient, we should decide what part of the cataract is due to the phakic IOL and what part is due to normal age-related changes. These highly myopic patients also tend to develop cataracts earlier than emmetropic patients, even if no prior surgery is performed. Look carefully at the eye using retro-illumination to determine if there are any iris defects and to check patency of the peripheral iridotomy.
Although the posterior chamber phakic IOL is unlikely to influence the optical coherence axial length measurements significantly, if data can be found from before the original surgery, it can be compared with current measurements for verification. Keep in mind that these eyes will have long axial lengths, and an appropriate method for IOL power calculation should be used. In addition, it is wise to err on the side of residual myopia instead of aiming for absolute plano.
At the beginning of the cataract surgery, viscoelastic can be injected under the phakic IOL to bring it into the anterior chamber. At this point, the phakic IOL can be firmly grasped with serrated forceps and pulled out through a standard 3-mm or smaller phaco incision. Cataract surgery can then proceed normally with implantation of the IOL into the capsular bag.
Click here to read the full publication exclusive, Back to Basics, published in Ocular Surgery News U.S. Edition, September 25, 2016.