Trabecular Micro-Bypass Stent Placement Influences Aqueous Angiography-Visualized Aqueous Humor Outflow in Human Eyes

Abstract

Purpose : Trabecular micro-bypass stents are a form of Minimally Invasive Glaucoma Surgeries (MIGS) that bypass the trabecular meshwork (TM) to improve aqueous humor outflow (AHO) to lower intraocular pressure (IOP). MIGS demonstrate inconsistent IOP lowering with one hypothesis related to improper placement.

Methods : Human enucleated eyes (n=7 eyes; 3 males and 2 females; 76-82 yo) were obtained within 48 hours of death from the San Diego Eye Bank. Aqueous angiography (AA) was performed with 0.4% ICG to determine the outflow patterns of an individual eye. Areas of low angiographic signal were marked. A full-thickness corneal incision was made and a trabecular micro-bypass stent (iStent G2W; Glaukos Corporation) or sham was conducted under direct visualization of the TM with subsequent closure of the corneal wound by glue. Subsequently, AA was performed with 2% fluorescein to query the influence of TM bypass. Eyes were fixed and paraffin embedded for histological sectioning (H&E stain) over the marked regions of stent placement to assess placement.

Results : In control human eyes (n=2), AA signal with fluorescein (after sham) was similar to that with ICG (prior to sham). With stent placement in low angiographic regions guided by ICG AA, 4 out of 5 eyes demonstrated improved signal with fluorescein AA. The level of improvement was related to the extent of TM opening and bypass seen by histology (Figure). One eye without improved AA signal was noted to have micro-bypass stent placement in the ciliary body.

Conclusions : Trabecular micro-bypass stent placement improves AHO as seen by AA, and the level of improvement is related to the quality of TM bypass.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

 

Fig. 1
Aqueous angiography (AA) was performed in three human eyes with indocyanine green (ICG; A-C). Trabecular (TM) micro-bypass stents (A/B) or sham (C) were placed in regions of low AA signal (A-C; red arrows). Repeat AA with fluorescein (D-E) showed significantly improved AA signal (D; arrow), partially improved AA signal (E; arrow), and no change (F; sham; arrow). Significantly improved AA (D) showed full thickness TM bypass (G; arrow and arrowhead) on histology whereas partially improved AA showed partial split thickness splitting of TM (H; arrow) with remnant TM strip intact (H; arrowhead). Normal angle structures are seen in the sham eye (I; arrow).