Don’t Fear the Defect

Cataracts associated with iris defects are an issue that every cataract surgeon will encounter, especially in patients who have experienced ocular trauma. Although these cases may seem daunting, there are a range of techniques available to tackle the problem – reviewed below.

Iris investigations

Since the cataract itself can be responsible for glare and photophobia, it’s useful to establish the presence or absence of photic symptoms before cataract formation, as this can guide your decision on whether or not to perform iris repair. Iris-associated ocular comorbidities are not unusual, and should be ruled out at the initial visit – this includes zonular weakness, vitreous prolapse, and damage to the trabecular meshwork or corneal endothelium (1).

We can subdivide iris defects into anatomic (which implies loss of iris tissue) and functional types. Anatomic defects can be either full-thickness, or involve only the loss of iris pigment epithelium (IPE), which is sometimes visible only by retroillumination. On the other hand, functional iris defects usually result in an atonic mydriatic pupil (Figure 1 a–c).

Biomicroscopy should be performed both before and after pharmacologic mydriasis. During the initial exam, it’s important to determine the number of clock hours affected by the iris defect – as a general rule of thumb, a primary repair can be planned if fewer than three clock hours are affected. In larger defects, an iris prosthesis should at least be considered. Gonioscopy is also very important, as it aids in finding peripheral iris defects, and can help in determining the status of the adjacent tissue around the original defect, as biomicroscopy alone could be misleading while determining the extent of the damage.

From full-thickness defects…

Our standard approach to focal full-thickness iris defects is using the modified Siepser knot (2) (Figure 2 a–b) with 10-0 Prolene sutures using a CTC-6L needle (Ethicon, Somerville, NJ, USA). When accessing the anterior chamber (AC) through a paracentesis, special attention should be paid to avoid catching any corneal fibers with the needle. To do this, take a first full-thickness bite into the proximal iris, then a second full-thickness bite into the distal iris, and then exit the globe through the limbus, using the sharpness of the needle. Next, gently remove the needle from the AC, making sure not to damage any structures with the trailing end when doing so. A Kuglen hook or a Condon snare (MST, Redmond, WA) can be used to retrieve the distal end of the suture through the proximal paracentesis, creating a suture loop next to the trailing end of the suture. Start the Siepser knot by inserting the distal end of the suture into the loop, and going around twice for the first knot. Apply tension to both ends of the suture, which forces the knot to slide into the AC, apposing both iris edges. Repeat the process, making sure to lock the knot by doing a specularly similar maneuver. We normally like to tie these knots in a 2–1–1 fashion before cutting the tags with intraocular scissors – but be extremely cautious not to inadvertently cut the knot. Repeat this process as many times as is necessary to close the full extent of the iris gap.

… to IPE and iridodialysis

Since focal IPE defects can be better recognized using retroillumination, it’s helpful to use a smaller coaxial light beam under the operating microscope, shining it through the pupil in order to reveal any hidden defects. For this type of focal defect, we use our recently published technique of iris oversewing (3) (Figure 3 a–c). Using the same principles mentioned for the Siepser knot, this involves entering the AC through a paracentesis with a 10-0 Prolene suture, but this time, instead of taking a full-thickness bite on the proximal iris, only grab healthy iris stroma, adjacent and proximal to the area of the defect. Then, the second bite is taken on healthy iris stroma, this time adjacent and distal to the defective area. After the creation of a Siepser knot, healthy iris stroma with underlying healthy IPE will cover the damaged area. Repeat the process with as many sutures as needed to fully cover the defect. With this technique, we are able to avoid creating any new pigment epithelium defects with the needle while passing the sutures, which could lead to new IPE defects from suture cheese wiring. As seen in Figure 3c, with the same retroillumination we can confirm disappearance of the initial defect.

In iridodialysis repairs, always consider the possibility of concomitant zonular dialysis and vitreous prolapse. We recommend the use of triamcinolone to stain the vitreous prolapse (4) previous to anterior pars plana vitrectomy. Use both needles of a 10-0 Prolene suture to create a mattress suture, which will appose the iris root to the scleral wall. If the pupil becomes distorted, after tying the first throw of the first knot, use microforceps to pull on the pupil until the shape is satisfactory, before locking the knot into position and burying it into the sclera, and finish the case.

Atonic pupils

Our procedure of choice for the management of an atonic mydriatic pupil is a pupillary cerclage (Figure 4, a, b). This usually requires three paracenteses separated by 120° (basically a triangle of paracenteses – although additional paracenteses can be used) and the same 10-0 Prolene suture on a CTC-6L needle to take multiple iris bites around the pupil margin. When retrieving the needle through one of the paracenteses, after the first third has been completed, thread the needle into a viscoelastic cannula to avoid catching any corneal fibers. Reenter the eye with the same needle, once again carefully avoiding catching any corneal fibers, and repeat the process in the two remaining thirds, occasionally using microforceps to provide some countertraction. In order to tie the final knot once the cerclage has been completed, exit the AC through the limbus with the needle and use the same Siepser knot, while titrating the necessary tension based on the desired pupillary size.

Pondering prostheses

When considering an iris prosthesis, there are a lot of things to take into account, including configuration of the iris defect, the importance of cosmesis to the patient, availability, and cost. There are many different iris prostheses available, but this can depend on geographical location. Small incision iris prostheses include the Morcher 50– and 96– series, which can generally be inserted through a 3.2 mm incision, and can achieve great success in limiting the amount of light that reaches the posterior segment. On the other hand, they do not provide a significant cosmetic improvement, since they are made of black polymethyl methacrylate.

Alternatively, the Humanoptics Customflex (Figure 5a) is a silicone, flexible iris prosthesis, customized based on a photo of the fellow eye, and provides excellent functional and cosmetic results. Sulcus placement of this device is possible, either passively or sclerally sutured, though we strongly encourage “in-the-bag” insertion (Fig. 5 b–c) in order to reduce uveal contact and reduce the risk of dislocation. Surgical steps for in-the-bag insertion include staining the anterior capsule with trypan blue, or alternatively indocyanine green (5), in cases where there are already fragile anterior capsules, such as in patients with congenital aniridia. Aim for a slightly larger than normal capsulorhexis (5.5 to 6 mm) to facilitate insertion of the device. We also recommend using a capsular tension ring in every case. Measure the capsular bag’s size with an intraocular ruler, and trephine the device based on this measurement. The device can be inserted into the AC using an AMO Silver Series injector, with the pseudopupil facing upwards, making sure that the leading edge goes underneath the distal edge of the previously stained anterior capsule. The unfolding process can be initiated using two opposing Kuglen hooks. Once the prosthesis has been unfolded inside the AC, opposing microforceps (through a paracentesis located 180° from the main wound) can be used to grab the pseudopupil’s edge and fold the prosthesis pseudopupillary edge over itself, reducing the prosthesis’ external diameter, and making it easier to fully insert the device into the capsular bag.

Don’t be disheartened

Irrespective of whether you’re dealing with congenital aniridia or traumatic iris damage, resolving iris defects successfully and to your patient’s satisfaction can be a challenge. But as techniques become more sophisticated and technologies and prostheses improve, it’s no longer a surgical issue to be feared. The selection of the most appropriate approach will depend on a range of factors, particularly the extent of the damage to the iris, ranging from primary closure of small defects to complete iris prostheses. These techniques should help you ensure that your patients experience the best possible visual and cosmetic postoperative outcomes. Don’t fear the technique, embrace it!

Mauricio A. Perez is cornea, cataract and refractive surgery specialist at Clinica Las Condes and Hospital Salvador, in Santiago, Chile, an anterior segment post-fellow at the University of Toronto and University of Cincinnati, and volunteer faculty at the University of Chile/Fundación Imagina.

Michael Snyder is a member of the board of directors at the Cincinnati Eye Institute, and is also a member of the volunteer faculty at the University of Cincinnati.