The Effect Of Glaucoma Surgeries On Aqueous Humour Outflow Facility

To compare the effect of trabecular-based (Gonioscopy Assisted Transluminal Trabeculotomy- GATT) and subconjunctival-based (Ahmed Glaucoma Valve – AGV and Preserflo Microshunt – PMS) glaucoma surgeries on aqueous humour outflow facility.

Prospective, before-and-after study.

Patients with primary or secondary open-angle glaucoma who were scheduled for GATT, PMS, or AGV surgery were included in the study. Patients without glaucoma undergoing cataract extraction alone served as controls. The pre-and-post operative intraocular pressure (IOP), number of medications, and biometric data were analyzed. The outflow facility coefficient (C) measured by pneumatonography (Model 30 Classic, Reichert Technologies, Depew, NY, USA) was compared preoperatively and 1 and 3 months post-operatively.

47 eyes were included: 20 in the GATT group, 12 in the PMS group, 5 in the AGV group, and 10 in the cataract extraction alone group. All patients in the GATT group underwent combined surgery with cataract extraction.

The preoperative C values (in μl/min/mmHg) for GATT, PMS, AGV, and cataract alone were 0.11, 0.08, 0.1, and 0.2 respectively. There was no significant difference between glaucoma patients in mean baseline IOP and C values. The C value increased significantly (p<0.001) at post-operative month 3 to 0.248, 0.27 and 0.2 in the GATT, PMS and AGV groups, respectively.

In the cataract extraction alone group there was no statistically significant change in IOP or C values before surgery (0.2) and at post-operative month 3 (0.215).

Outflow facility increased significantly after both trabecular-based and subconjunctival-based glaucoma surgery, but not after cataract extraction alone three months after surgery. In well-selected patients, GATT was not inferior in improving outflow facility to glaucoma drainage implants.