Intraocular Pressure Spikes Following iStent Inject and the Relationship to Aqueous Outflow in Open Angle Glaucoma.

PRECIS: Adding TBS to phacoemulsification creates unpredictable short-term IOP control that may be undesirable for patients with advanced glaucoma. AO responses after TBS are complex and probably multifactorial.

PURPOSE: To assess intraocular pressure spikes in patients with open angle glaucoma up to one month following iStent Inject and their relationship to aqueous outflow patterns measured by Hemoglobin Video Imaging.

PARTICIPANTS AND METHODS: We studied IOP for 4 weeks after trabecular bypass surgery (TBS) with iStent Inject in 105 consecutive eyes with open-angle glaucoma (6 TBS only and 99 combined with phacoemulsification). The change in IOP after surgery at each time point was compared with baseline measurements and the prior post-operative visit. IOP-lowering medications were stopped on the day of surgery in all patients. A smaller pilot study of 20 eyes (TBS only=6 and Combined=14) underwent concurrent Hemoglobin Video Imaging (HVI) to observe and quantify peri-operative aqueous outflow. Aqueous column cross-sectional area (AqCA) of one nasal and one temporal aqueous vein was calculated each time point, and qualitative observations were documented. An additional 5 eyes were studied after phacoemulsification only.

RESULTS: Mean IOP for the entire cohort (pre-operative 17.3±5.6 mmHg) was lowest the day after TBS (13.1±5.0 mmHg) and peaked at 1 week (17.2±8.0 mmHg), before stabilizing by 4 weeks (15.2±5.2 mmHg; P<0.00001). The same IOP pattern was seen when separating the group into a larger cohort without HVI (respectively 15.9±3.2 mmHg, 12.8±4.9 mmHg, 16.4±7.4 mmHg and 14.1±4.1 mmHg; N=85, P<0.00001) and the smaller HVI pilot study (respectively 21.4±9.9 mmHg, 14.2±4.9 mmHg, 20.2±9.7 mmHg, and 18.9±7.6 mmHg; N=20, P<0.001). More than 30% IOP elevation above baseline occurred in 13.3% of the entire cohort at one week after surgery. This increased to 46.7% when IOP was compared with one day after surgery. Inconsistent AqCA values and patterns of aqueous flow were demonstrated after TBS. AqCA after phacoemulsification alone was maintained or increased within one week in all 5 eyes.

CONCLUSION: Following iStent Inject surgery in patients with open angle glaucoma, intraocular spikes were most commonly seen at one week. Aqueous outflow patterns were variable and additional studies are needed to understand the pathophysiology underlying intraocular pressure responses after this procedure.