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.
Anterior chamber phakic IOLs
These rigid phakic IOLs are clipped to the anterior surface of the iris for stability. Because they are made of stiff PMMA material, they require a large incision for implantation. Typically, this is made as a superior scleral tunnel of at least 6 mm in width. This will certainly induce some degree of astigmatism as it heals, and it is not unusual to find these patients with a large degree of against-the-rule astigmatism years later. When these patients develop cataracts, it is typically age-related and not due to touch of the anterior lens capsule, which is protected by the iris.
Preoperative assessment should look again for any iris damage, particularly at the site of the iris clips, and for patency of the peripheral iridotomy. The corneal endothelium should be examined for cell density and dropout, which can happen with long-term anterior chamber phakic IOL placement. Corneal topography will confirm the degree and axis of astigmatism, which is typically around the 180° meridian due to the previous surgical incision.
Anterior chamber phakic IOLs are significantly thicker than posterior chamber phakic IOLs, and they can induce more error when biometry is done with A-scan ultrasound. In particular, the A-scan may read a shallower anterior chamber depth and perhaps a change with the axial length as well. Optical coherence biometry will be less affected, and its degree of error can be easily offset by choosing a slightly myopic refractive target.
Cataract surgery in an eye with an iris-claw anterior chamber phakic IOL is significantly more challenging. Careful marking of the steep corneal axis should be done ahead of time, and this will likely be against-the-rule astigmatism at about the 180° axis. The standard phaco incision of 3 mm or less should be made temporally on the steep axis. Then the phakic IOL should be held firmly with forceps, and the iris stroma should be gently removed from the clips to fully free it. Additional viscoelastic is injected to protect the corneal endothelium. At this point, a second incision opposite of the main phaco incision is created. This incision will help to further neutralize the pre-existing against-the-rule astigmatism. It needs to be 6 mm wide and made in a shelved manner in order to maximize stability and sealing.
This incision can be a challenge to make because it is placed nasally. The phakic IOL can then be pushed out of this nasal incision and removed completely. This large incision should be sutured before beginning the cataract removal in order to maximize stability during phacoemulsification. Once the final IOL is placed in the capsular bag and the viscoelastic removed, all incisions can be checked with fluorescein dye and additional sutures can be placed as needed.
Phakic IOLs can be a benefit to highly myopic patients for many years, but eventually they will need to be removed once the eye develops a cataract. Phakic IOLs can make cataract surgery more challenging, but with careful planning and specialized techniques, we can achieve excellent visual results for our patients.
- For more information:
- Uday Devgan, MD, is in private practice at Devgan Eye Surgery, Chief of Ophthalmology at Olive View UCLA Medical Center and Clinical Professor of Ophthalmology at the Jules Stein Eye Institute, UCLA School of Medicine. He can be reached at 11600 Wilshire Blvd. #200, Los Angeles, CA 90025; email: firstname.lastname@example.org; website: www.DevganEye.com.
Disclosure: Devgan reports no relevant financial disclosures.