By Gail F. Schwartz, MD
The authors of this prospective study sought to determine the association of changes in anterior chamber angle and anterior chamber depth (ACD) with IOP reduction after uncomplicated phacoemulsification. They followed eyes with narrow irideocorneal angles (NA) and open angles (OA) for six months after surgery. As expected, IOP lowering was greater in eyes with shallower anterior chambers than the deeper controls, with IOP reduction per 0.1-mm increase in angle opening distance at 500 μm anterior to the scleral spur (AOD500) in NA eyes greater than in OA eyes. While it is well-established that uncomplicated phacoemulsification can result in IOP lowering, measurement of ACD with Visante anterior segment OCT (AS-OCT), as was done in this study, certainly adds to the knowledge base.
However, this study, which was published in October in the Archives of Ophthalmology, would have been even more interesting if another arm was included with narrow-angle patients with elevated IOP or angle-closure glaucoma patients, as those with greater possible or demonstrated pathology may respond differently. Additionally, since previously published studies suggest that the IOP-lowering effect of phacoemulsification may not be sustained beyond one year, longer term follow-up would help support or refute this.
The study included 63 eyes that underwent phacoemulsification with foldable lens implantation. Twenty-six eyes were classified as NA, defined as anterior chamber angle grading of 2 or less (Shaffer grading) in three or all quadrants. AS-OCT and tonometry were performed preoperatively and 10 days and one, three and six months after surgery. ACD and AOD500 were assessed from AS-OCT.
In the NA group, the mean (SD) AOD500 changed from 0.179 (0.014) mm before surgery to 0.389 (0.025) mm six months after surgery and the mean (SD) ACD from 2.23 (0.07) mm to 3.75 (0.05) mm. Six months after surgery, the mean (SD) IOP reduction was 2.75 (0.60) mm Hg (17.82 percent) in the NA group and 1.55 (0.47) mm Hg (9.6 percent) in the OA group, which was significantly different between the two groups (P=.004). Each 0.1-mm increase in AOD500 corresponded to a mean (SD) 0.42 (0.18)-mm Hg decrease in IOP (P < 0.001) in the NA group and 0.32 (0.16) mm Hg (P=.046) in the OA group.
The authors conclude that phacoemulsification with IOL implantation results in deepening of the central anterior chamber, widening of the anterior chamber angle and lowering of IOP in NA and OA eyes. They say that glaucoma patients with more NAs before phacoemulsification may experience greater IOP lowering afterward and a greater possibility of discontinuing one or more medications postoperatively. They propose that preoperative angle assessment may be helpful in predicting the IOP benefit of cataract extraction, although the exact mechanism of IOP reduction after cataract surgery is still not fully understood.