• glaucoma

Posterior synechiae are common complications of anterior uveitis, and can result in pupillary seclusion, iris bombé and angle-closure. In this issue of the journal, Betts and associates1 describe their experience in managing such patients. Despite the limitations of a non-randomised, retrospective study, their results support the assumption of many uveitis and glaucoma experts that patients with uveitis whose disease is complicated by iris bombé from extensive posterior synechiae should have surgical iridectomies rather than laser iridotomies. The authors’ patients who were managed surgically had a markedly lower risk of treatment failure. Why the difference in outcomes? Laser iridotomies may stimulate more inflammation than surgical iridectomies, causing an outpouring of fibrin from the laser iridotomy site, which will eventually close the small, irregular opening. In contrast, surgical iridectomies are larger; with sharp, well-defined edges; and they tend to be more peripheral, all factors reducing the risk that the opening will scar closed.

Inflammation at the time of the iris procedure was not identified as a significant risk factor for failure in the current authors’ series, but one cannot assume that lack of anterior chamber cells or substantial clinical flare confers no risk of failure. Their analysis showed that inflammation at the time of the procedure had a HR of 1.5, suggesting a greater risk of failure among those with laser iridotomies, although the association was not statistically significant. There were far more laser procedures than surgical procedures, and they did not state how the 86 episodes of active inflammation (among a total of 131 procedures) were distributed between the subgroups based on technique; thus, the lack of a statistical association may have been a sample size issue. They did find that postoperative inflammation was a risk factor (possibly associated with the inflammation stimulated by laser procedures). In addition, they found a marked difference in survival of the iris opening between patients with histories of uveitis and primary, rather than secondary, angle-closure glaucoma (presumably without inflammation at the time of angle closure) versus those with secluded pupils from inflammation. These observations reinforce the well-accepted notion that operating on inflamed eyes is associated with a substantial risk of complications.

One should consider whether an iris procedure is required at all for a given patient with uveitis, even if the person presents with a nearly secluded pupil. Paradoxically, a laser procedure can precipitate angle closure. A pupil will almost never completely seclude if adequate anti-inflammatory therapy is being given and there are no fibrin clots in the pupillary plane, even if there are nearly 360° of posterior synechiae. The high volume of aqueous humour flowing through the remaining pupillary opening, relatively speaking, prevents the iris in that area from touching the lens capsule, thereby preventing additional synechiae formation. If a laser iridotomy is performed, fluid is redirected through the iridotomy, removing the flow that might be preventing completion of pupillary seclusion. There may then be an outpouring of fibrin from the iridotomy site, which eventually will close the small, irregular opening, resulting in iris bombé and angle closure. In patients receiving adequate anti-inflammatory treatment and no iris bombé, we do not perform prophylactic laser iridotomies or surgical iridectomies.

In cases that do require a procedure (patients who have pupillary seclusion and iris bombé at presentation or patients who are poorly compliant to treatment recommendations), surgical iridectomies not only have a lower risk of failure, but they offer additional advantages over a laser iridotomy. Patients may have bands of adhesions between the posterior iris surface and the anterior lens capsule (rather than synechiae only at the pupillary margin), creating multiple areas of segmental iris bombé, which will not be relieved with a single opening in one area of the iris. A surgical procedure will allow infusion of a viscoelastic substance through the iridectomy, which will lift the iris away from the lens, creating a single contiguous space in the posterior chamber. An additional important opportunity afforded by access to the anterior chamber during surgical iridectomy is the chance to reopen an appositionally closed angle that has not yet developed permanent synechial occlusion, by gently infusing viscoelastic substance into the angle in a sweeping motion. This manoeuvre separates apposing iris from angle structures before permanent synechiae can form. In contrast to patients with primary angle closure, those with uveitis may have fibrin that continues to ‘glue’ the angle shut even after creation of a patent opening in the peripheral iris. This situation can be remedied during surgical, but not laser, intervention.

In summary, there are multiple advantages to surgical iridectomies over laser iridotomies in patients with anterior uveitis and posterior synechiae; however, clinicians should first consider whether a procedure is necessary at all. A laser iridotomy, in particular, might have unintended consequences.