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Elliott D.K. Cha, Jia Xu, Haiyan Gong; Variations in Active Areas of Aqueous Humor Outflow Through the Trabecular Outflow Pathway. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4850.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies in human eyes suggest that outflow through the trabecular meshwork (TM) and inner wall (IW) of Schlemm’s canal is segmental. Whether these patterns are conserved in distal outflow pathways remains to be determined. This study aims to evaluate variations of active outflow along the trabecular outflow pathway in three distinct regions: TM, IW and episcleral veins (EPV); and to develop a simple imaging method to assess active outflow areas on a whole eye scale.
Six normal human eyes were perfused for 30 minutes at 15mmHg to establish a baseline outflow facility. The anterior chamber of each eye was exchanged (5mL) and perfused with a fixed volume of fluorescent microspheres (200μL) to label outflow patterns. All eyes were perfusion fixed. Anterior segments were dissected and the TM and EPVs were en face imaged globally. Global images were analyzed for tracer distribution and intensity using an ordinal scale and effective filtration area (EFA) was measured. Anterior segments were dissected into a minimum of 16 radial wedges. Frontal sections were cut from each wedge, imaged for tracer distribution along the IW by confocal microscopy, as well as both EFA and number of collector channels (CC) analyzed. Student’s t-test and correlation analysis was performed.
Average baseline outflow facility was 0.18±0.08 μL/min/mmHg. Active outflow in the TM showed a less segmented pattern and a significantly higher EFA (84.06±5.89%) than both the IW (35.32±5.03%) and EPVs (32.31±3.90%; p<0.05). Comparisons of IW and EPV EFA revealed differences on an individual wedge basis, but a similar percentage of EFA was found on a whole eye basis (p>0.05). Quadrant analysis of tracer distributions in EPVs revealed a preferential flow to both the nasal and inferior quadrants. No preference was found in the TM. Both IW and EPV EFA was significantly higher when one or more CCs were observed compared to no CCs (p<0.05; p<0.01).
Percentage of EFA was found to be similar in both IW and EPVs. Therefore, determining EFA in EPV could be used as a simple and useful tool to determine the area of active outflow on a whole eye scale, which may have clinical implications for future management of glaucoma.
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