Post-cataract surgery IOP reduction appears proportional to increase in angle width

This prospective study evaluated the effect of phacoemulsification on the anatomy of the drainage angle in narrow irideocorneal angle (NA) eyes compared with those with open irideocorneal angles (OA) and found that postoperative IOP reduction was proportional to the increase in angle in both groups. But the IOP reduction was greater in NA eyes. While these finding are intuitively obvious to me, they are nicely confirmed here.

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. Anterior segment optical coherence tomography (AS-OCT) and tonometry were performed before and after surgery. The ACD and angle opening distance at 500 μm anterior to the scleral spur (AOD500) were assessed from AS-OCT.

Before surgery, the mean (SD) ACD was 2.23 (0.07) mm in the NA group and 2.76 (0.08) mm in the OA group. After cataract surgery, the ACD deepened significantly in both groups (P<.001 in both groups), and thereafter no significant changes were observed throughout the postoperative period in any group (P >.05). The NA group had smaller values but deepened 0.313 (0.05) mm more than did the OA group (P<.001). The amount of IOP reduction was approximately 18 percent in NA eyes and 10 percent in OA eyes. The postoperative reduction in IOP was proportional to the increase in angle width in NA and OA eyes.

In the NA group each 0.1-mm increase in AOD resulted in a mean (SD) decrease of 0.42 (0.18) mm Hg in IOP (P=.001). In the OA group, each 0.1-mm increase in AOD corresponded to a mean (SD) decrease of 0.32 (0.16) mm Hg (P=.046).

The results suggest 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. The authors say this is the first study to demonstrate that postoperative reduction in IOP is related to increase in angle width after phacoemulsification in NA and OA eyes.

They conclude 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 say 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. Access of aqueous to the filtering portion of the trabecular meshwork may improve due to widening of the drainage angle.