The Correlation Between Aqueous Humor Flow and IOP Before and After Trabectome: Developing a Grading System to Quantify Flow

INTRODUCTION: To develop a grading system that provides objective quantification of flow through the conventional aqueous humor outflow (AHO) system. The technique gives clinicians an additional assessment option in the evaluation of glaucoma treatment approaches. METHODS: This was a retrospective observational study. This study evaluated the eyes of all primary open-angle glaucoma patients who underwent a Trabectome (NeoMedix Corp., Tustin, CA, USA) procedure with or without cataract surgery in the interval between April and September 2016 (n = 73). The nasal hemisphere was divided into three regions. Utilizing a four-level grading system designed for this study, an aqueous humor outflow grade (G0–G3) was assigned to each region using a video taken during examinations. The individual grade levels of the three regions were combined to get a composite AHO score. The correlation between the composite AHO score and intraocular pressure (IOP) was then analyzed. Additionally, the speed of red blood cell (RBC) clusters in the episcleral veins (ESV) was calculated when made possible by the existence of pulsatile flow. RESULTS: At 3 months following the Trabectome procedure, average IOP decreased from 26 to 15 mmHg. Assessment of the relationship between AHO grade and IOP demonstrated that a high composite AHO score was correlated with lowered IOP (Tukey-Kramer method p < 0.05). Additionally, it was found that if one of the three regions had an AHO grade of ≥ G2, an IOP of < 20 mmHg could be predicted. (Fischer’s exact test p < 0.0001). Calculated speed was as follows: at G1, the speed was 0.68 ± 0.26 mm/s (n = 7), at G2, the speed was 1.8 ± 0.84 mm/s (n = 5), and at G3, the speed was 6.8 ± 3.3 mm/s (n = 6). CONCLUSION: There was a significant correlation between an increase in the composite AHO score and a decrease in IOP. Additionally, the speed of RBC clusters as they traveled through the ESVs remained consistent for each of the grades, and the span of the speeds from lower to higher grades represented a significant range. These findings suggest that the grading system is a reliable measure of AHO. TRIAL REGISTRATION IDENTIFIER: UMIN 000031745.