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By Cheryl Guttman Krader
Laser-based options for treating angle closure glaucoma include laser iridotomy, laser iridoplasty, and endocycloplasty. Among those procedures, however, only laser iridotomy has a definitive role, according to Shan C. Lin, MD.
Laser iridotomy came to be considered first-line treatment for angle closure glaucoma based on the idea that pupillary block, which is relieved by laser iridotomy, accounts for about 90% of cases of angle closure glaucoma. Although it is now recognized that plateau iris has a significant etiologic role, Dr. Lin said it makes sense to perform laser iridotomy first.
Figure 1. A. Nanophthalmic eye with patent but small patent iridotomy showing shallow peripheral anterior chamber (grade 1 on gonioscopy). B. Same eye after enlargement of the peripheral iridotomy showing deepening of the peripheral chamber (grade 3 on gonioscopy)
“In eyes with plateau iris, there is usually a mixed mechanism for angle closure glaucoma that includes pupillary block,” explained Dr. Lin, professor of ophthalmology and director of the Glaucoma Service, University of California, San Francisco. “Laser iridotomy will remove the pupillary block component and is also needed to know whether or not plateau iris is the primary mechanism.”
Laser iridotomy is indicated in eyes with at least 180º of an occludable angle (grade 0 or 1). Providing some tips on technique, Dr. Lin recommended doing the laser iridotomy in the horizontal position because published data show that it is associated with less photopsias than a superior approach.
He said he would avoid laser iridotomy in a patient who has ≥180º of peripheral anterior synechiae (PAS) because the procedure may only worsen the situation.
“The angle is already mostly or entirely zipped closed in these eyes,” Dr. Lin said. “Therefore, inflammation induced by the laser treatment will be trapped inside the angle, the IOP will spike, and the elevation may be persistent.”
Discussing enlargement of an iridotomy, Dr. Lin said patency with an opening of 150 µm to 200 µm might not be enough for judging iridotomy sufficiency. He illustrated the role of iridotomy enlargement by presenting a case of a nanophthalmic eye with a narrow angle and patent iridotomy that benefited after enlargement of the iridotomy (Figures 1 and 2).
Whether or not there is a role for laser iridoplasty as a second-line treatment in eyes with a narrow or closed angle after laser peripheral iridotomy is a matter of debate. Potential complications of the procedure include IOP spike and induction of PAS, and those risks need to be weighed against the paucity of evidence demonstrating that laser iridoplasty opens the angle and prevents glaucoma.
Dr. Lin noted that a paper published in 2007 by Ritch, et al. reporting laser iridoplasty was effective in many cases led him to believe it was worth a try. However, his opinion changed when a paper published in 2010 represented the only prospective, randomized study on this topic.
Conducted in China, that trial randomized 156 eyes with primary angle closure or primary angle closure glaucoma to iridotomy alone or combined with iridoplasty, regardless of whether iridotomy opened the angle. Outcomes after 1 year of follow-up indicated the addition of iridoplasty to iridotomy was safe, but did not seem to confer any real benefit.
Corneal endothelial cell counts were unchanged in both groups and there were no significant differences between groups in overall complications. IOP reduction was the same in the two groups, and the only difference was 1 clock hour less of PAS development in eyes treated with iridoplasty plus iridotomy.
“Doctors who have a laser available may not be afraid to use it to open a narrow angle, but this study helped to convince me that iridoplasty may not be doing all that much,” Dr. Lin said.
Figure 2. A. Anterior segment optical coherence tomography of same nanophthalmic eye in Figure 1, showing very narrow or occluded angles. B. Same eye after enlargement of the iridotomy, showing substantial increase in the angle width.
Endocycloplasty is a modification of endoscopic cyclophotocoagulation that aims to cause iris retraction leading to opening of the angle. The treatment is usually combined with phacoemulsification and is performed by aiming the laser toward the posterior portion of the ciliary processes, leading to shrinkage and posterior rotation of the ciliary body.
Dr. Lin noted that it remains to be determined whether endocycloplasty has any additional benefit when performed with phacoemulsification, and he suspects that phacoemulsification alone might be sufficient intervention for reducing IOP in eyes with angle closure glaucoma as well as for opening of the angle.
According to findings of a meta-analysis conducted by the Ophthalmic Technology Assessment Committee of the American Academy of Ophthalmology, eyes with chronic angle closure glaucoma benefited with a 29% reduction in IOP after phacoemulsification and about a 50% decrease in medication use. The benefits of phacoemulsification were even more impressive among eyes with acute angle closure glaucoma.
Consistent with the findings of the meta-analysis, a published paper reviewing outcomes of 5 eyes with acute or chronic angle closure glaucoma that underwent clear lens extraction found 4 eyes benefited with lowering of IOP to <21 mm Hg and a reduction or elimination of medication.
The report of the American Academy of Ophthalmology Ophthalmic Technology Assessment will be published in Ophthalmology.