Reply: We have not had experience using the Graether ring as an alternative to iris hooks in these patients, but we think the purpose of using iris hooks may have been missed. In iridoschisis, the posterior layer of the iris is usually intact and the sphincter and dilator muscles function in a normal manner.1 Pupil dilation is therefore not usually the problem; the problem is with the wispy fibers of degenerated iris tissue. The iris hooks are used to control these fibers rather than dilate the pupil. Careful surgical technique and gentle handling do not result in sphincter ruptures in these cases.
As the fibers degenerate, they take on a “shredded wheat” appearance. The broken fibers remain attached at the iris sphincter and ciliary body but may float forward into the aqueous.2 We believe that engaging the pupillary margin will not trap them, as was explained in our paper. The pupil dilator may also be considered as it provides additional pupil dilation and its rim may trap some of the fibers at the pupillary margin. However, long, free-floating, torn fibers may not be trapped and may still extend over the rim into the dilated pupil aperture and surgical field. Untrapped fibers caught by the phacoemulsification tip or aspiration cannula may hemorrhage from their arterioles or excite postoperative inflammation.3
If a temporal approach is used and the Graether ring does not trap the fibers in the 3.75 mm gap, free fibers are at risk of being engaged by the aspirating instruments. A superiorly sited wound, on the other hand, allows working over the superior iris, which is usually much less severely affected than elsewhere.1 In addition to fibrillary degeneration of the iris and cataract formation, iridoschisis is associated with narrow drainage angles.1 The slender iris hooks are easily manipulated and removed, minimizing the trauma to intraocular structures, such as the corneal endothelium, that may occur with more bulky devices.
We acknowledge that the additional paracenteses could be avoided by using a Graether ring, but the paracenteses are astigmatically neutral and 4 or 5 are sufficient in most cases. We have not found that iris hooks interfere with surgery when placed posteriorly along the iris plane to avoid “tenting.” One of us has since operated on 2 cases of iridoschisis through clear corneal incisions using the phaco-chop technique. In the first, there was only a slight shredded wheat appearance to the iris fibers. The iris degeneration did not appear sufficiently severe to warrant the use of iris hooks, a decision soon regretted by the surgeon. The second case appeared more severely affected; iris hooks were used, and the surgery was completed without difficulty.
The Graether ring, or other pupil expansion rings, may offer advantages when the anterior chamber is deep, the iris fibers have only a mild shredded wheat appearance, and poor pupil dilation is more of an issue. However, iris hooks have become widely available and most surgeons are already familiar with their use.
Guy T Smith FRCOphth
Christopher S.C Liu FRCOphth
1. Albers EC, Klein BA. Iridoschisis: a clinical and histopathologic study. Am J Ophthalmol 1958; 46:794-802
2. Loewenstein A, Foster J. Iridoschisis with multiple rupture of the stromal threads. Br J Ophthalmol 1945; 29:277-282
3. Smith GT, Liu CSC. Flexible iris hooks for phacoemulsification in patients with iridoschisis. J Cataract Refract Surg 2000; 26:1277-1280