Trabecular Meshwork Pigmentation is Only Weakly Related to Angiographically Determined Aqueous Humor Outflow

Abstract

Purpose : The extent of trabecular meshwork (TM) pigmentation has been hypothesized to be a non-invasive proxy of segmental aqueous humor outflow (AHO), where increased pigmentation may be associated with increased AHO. In the present study, we set out to compare TM pigmentation with angiographically determined aqueous humor outflow signal intensity.

Methods : Post-mortem human (n=7) eyes were acquired from San Diego Eye Bank. Extraocular muscles were used to determine the orientation of the eyes, and anterior segments were dissected. A magnified image of the TM was circumferentially acquired from a clinical surgical microscope. Anterior segments were then mounted onto a perfusion chamber and perfused with Dulbecco’s phosphate buffered solution containing glucose using a constant-flow paradigm to achieve a stable baseline outflow facility. Fluorescein was then perfused into the anterior chamber, and outflow in conventional AHO pathways was imaged using a fluorescent camera with appropriate filters. The pigmentation intensity profiles as well as the angiographic outflow signal intensity profiles were extracted from the acquired images using ImageJ and converted to an 8-bit scale (0-255, arbitrary units). The two modalities were compared in 5-degree bins with 0, 90, 180, and 270 degrees being superior, temporal, inferior, and nasal, respectively.

Results : Overall, a statistically significant, but weak negative correlation was observed (r= -0.101, p=0.023) between TM pigmentation and AHO angiographic signal. The highest pigmentation intensity was observed inferiorly (169.52 [arbitrary units] at 215-220 degrees), whereas the outflow angiographic intensity was most pronounced nasally and temporally (140.62 at 50-55 degrees and 183.15 at 280-285 degrees).

Conclusions : There is a weak and negative correlation between TM pigmentation and angiographic AHO. Thus, clinical evaluation of TM pigmentation is not a reliable surrogate parameter for AHO in conventional pathways, and it does not appear to be useful as a guide for placement of angle-based glaucoma surgery.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.