First installment of a new column devoted to solving challenging cases in the clinic and operating room.
The use of IOLs transformed the world of cataract surgery decades ago, with the standard being implantation into the capsular bag. When all goes well, the resultant vision is superb with a high level of patient satisfaction. But when the IOL is significantly decentered, it will negatively affect vision and may cause additional adverse effects.
Patients with dislocated IOLs often present with symptoms such as a drop in acuity, glare or other visual effects from having the edge of the optic splitting the pupil. They may have a history of slowly progressive symptoms or a sudden onset, such as after trauma. The key is determining the current position of the IOL, the reason for its dislocation and whether an IOL exchange should be performed.
Current IOL position
IOLs that are completely within the capsular bag usually have a high level of stability, but zonular weakness, such as in pseudoexfoliation syndrome, can cause lens dislocation. This can range from a mild decentration of the lens without symptoms to a complete posterior dislocation of the entire bag-IOL complex into the vitreous. Phimosis of the anterior capsular rim can cause the zonules to break and the IOL to become distorted and shift from the visual axis.
IOLs in the ciliary sulcus, often placed there at the time of cataract surgery due to a break in the posterior capsule, are inherently less stable and may shift or dislocate. If a sulcus IOL is mildly decentered, this can be due to a simple sizing issue: The overall length of the IOL may be too small for the sulcus, and thus the optic position may deviate from its intended position. In some cases, sulcus IOLs can be stable for many years and then shift due to trauma.
If an IOL is placed in a capsular bag with a defect of the posterior capsule, it may end up in the vitreous. The reason we prefer to convert a small break of the posterior capsule into a small round posterior capsulorrhexis is to provide strength and resistance to further tearing. If the posterior capsule break extends in the immediate postoperative period, the IOL can dislocate into the vitreous. If vitreous strands are enveloping the IOL, a careful vitrectomy will need to be performed at the time of IOL repositioning or exchange.
Reason for dislocation
Common reasons for IOL dislocation include posterior capsule defects, broken or weak zonules, and malpositioned IOLs. Sometimes, the existing IOL can simply be repositioned or suture fixated in the eye, which can be accomplished with smaller incisions and a less-invasive technique.
The level of existing capsular support is important for surgical planning. Patients with a sufficient anterior capsular rim can have the IOL placed in the sulcus or via optic capture with good long-term stability. In patients with inadequate capsular support, the IOL may need to be sutured into position or exchanged for an anterior chamber IOL. In cases of a damaged primary IOL or incorrect IOL power, an IOL exchange may be warranted.
Another potential issue is placement of an inappropriate type of lens for the location in the eye. Placing a single-piece acrylic lens, which is designed solely for in-the-bag implantation, in the ciliary sulcus can lead to dislocation and other more serious issues. The thick haptics of a single-piece IOL can chafe the posterior surface of the iris, leading to pigment dispersion, iris defects, micro-hyphema, chronic inflammation and ocular pain. These IOLs must be removed from the ciliary sulcus and replaced with a different IOL. (Article continues below…)
If the IOL will be exchanged, calculations for the new lens implant should take into consideration the effective lens position of the optic within the eye. If the IOL is completely in the sulcus, the optic will be more anterior and the power should be decreased by 0.5 D to 1 D in most eyes. With haptics in the sulcus but the optic buttonholed through an intact capsulorrhexis, the IOL power is about the same as with primary in-the-bag placement. Iris-sutured IOLs and scleral-sutured IOLs end up having the same power calculations as in-the-bag placement. Anterior chamber IOLs have lower A-constants because they have the most anterior effective lens position.
Simple re-centration of an appropriate IOL in the sulcus, in an area of greater capsular support, may be sufficient. In other cases, suture fixation of an IOL to the iris or the sclera can give greater stability, although there can be issues with long-term degradation of the suture material. Rigid single-piece PMMA IOLs are available with eyelets in the haptics to allow for easier transscleral fixation. Foldable, three-piece acrylic or silicone IOLs are also appropriate for suture fixation. There is no consensus as to the best suture material, with surgeons using Prolene, polyethylene and even Gore-Tex with success.
The most appropriate IOLs for the ciliary sulcus are those that are designed to be there, or larger three-piece lenses, either silicone or acrylic, with posterior angulation of the haptics, thinner optics and a rounded edge to prevent damage to the iris.
Placement of an anterior chamber IOL can often produce excellent results with a relatively easy technique that does not require suturing of the IOL. The anterior chamber IOL should be matched to the anterior chamber dimensions, and a peripheral iridotomy or iridectomy should be performed to prevent pupillary block.
When removing the existing IOL, it is important to do so atraumatically and with as small an incision as possible. Foldable IOLs made of acrylic or silicone may be cut in the eye or even refolded to facilitate removal via a corneal incision of approximately 3 mm. Rigid PMMA IOLs must be removed via larger incisions of 6 mm or wider made in the sclera. Once the old IOL is removed, the anterior segment should be checked for the presence of vitreous before inserting the new replacement IOL.
To fixate a three-piece IOL to the iris, it should first be centered in the pupil and then the optic brought forward to secure it for suturing. This optic capture technique keeps the IOL centered and the haptics securely against the posterior surface of the iris. The suture is passed through the mid to mid-peripheral iris, under the haptic and back through the iris. Before cinching down the knots, the iris tissue is pulled centrally to ensure it is not bunched up under the suture material. This will avoid an ovoid pupil appearance after surgery, which can happen when excess iris tissue is incarcerated in the suture.
The common methods for suturing are the McCannel technique, which requires an additional incision near the knot, and the Siepser technique, which does not. Once the two knots are securely tied, the optic is pushed posterior to the iris. The recommended suture pattern is 3-1-1, with the suture ends kept slightly long to avoid future unraveling.
In cases in which there is iris loss, atrophy or weakness, it may be preferable to fixate the IOL to the scleral wall using sutures or an intrascleral technique. To protect the sutures used in scleral fixation, scleral pockets can be created posterior to the limbus and 180° apart, providing two points of contact but still allowing the IOL to rotate or twist. Often referred to as the glued IOL technique because of the tissue adhesive used, this technique can offer greater stability because intrascleral tunnels are created and the haptics of the three-piece IOL are placed securely within.
For patients who require surgery to fixate and center an IOL, the risk of complications is greater than in primary cataract surgery. Patients should expect at least a few weeks for inflammation to resolve and for return of best vision. Results can be dramatic, with improved vision for the patient and satisfaction for the surgeon.
Uday Devgan, MD, FACS, FRCS, can be reached at Devgan Eye Surgery, 11600 Wilshire Blvd., Suite 200, Los Angeles, CA 90025; 800-337-1969; fax: 310-388-3028; email: firstname.lastname@example.org; website: www.DevganEye.com.
Disclosure: Dr. Devgan has no relevant financial disclosures.