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Editors Selection IGR 12-2
Basic Science: Trabecular Pigmentation is not correlated to Outflow
Comment by Rami Darwich & Arthur Sit on:
112998 Lack of Correlation Between Segmental Trabecular Meshwork Pigmentation and Angiographically Determined Outflow in Ex-Vivo Human Eyes, Strohmaier CA; Wanderer D; Zhang X et al., Journal of Glaucoma, 2023; 0:
Some surgeons use trabecular meshwork (TM) pigmentation observed through gonioscopy as a biomarker to determine the optimal location for minimally invasive glaucoma surgeries, hypothesizing that TM pigment deposition correlates with areas of varying aqueous humor outflow (AHO). Strohmaier et al. investigated this relationship using fluorescein aqueous angiography with seven postmortem human eyes from older adults, excluding those with ocular diseases or prior surgeries, except for cataract surgery. The eyes were bisected, and TM pigmentation was photographed before mounting the anterior segments on a custom- made perfusion apparatus for assessment of AHO angiography.
No statistically significant correlation between segmental TM pigmentation and segmental AHO angiographic signal was found
They found no statistically significant correlation between segmental TM pigmentation and segmental AHO angiographic signal (r = −0.083, P = 0.06). However, A significant weak negative correlation was observed when analyzing the nasal quadrant specifically (r = −0.296, P = 0.001).
The study had limitations, including the use of eyes from individuals without glaucoma. Some glaucoma types, such as pigmentary glaucoma, can exhibit dynamic TM pigmentation patterns which complicates any attempt to correlate AHO with pigmentation.1 Additionally, the authors did not address the potential impact of their tissue processing methods on tissue pigmentation, an issue noted in a previous study by the group that necessitated rinsing with a balanced salt solution.2
Furthermore, it is possible that the custom-made system used in the study might not accurately replicate in-vivo outflow dynamics of the eye. Stripping the ciliary body, ciliary muscles, and the iris, could potentially traumatize the conventional outflow system and alter segmental outflow patterns. This could explain why the AHO angiography results showed no significant differences in signal between the different quadrants (nasal, temporal, superior, and inferior). It is also possible the sample size was simply too small to detect an association between pigmentation and AHO given the high degree of individual variability, a limitation the authors acknowledge.
Nevertheless, this study provides important information for MIGS procedures. Even if the sample size were expanded enough to detect a correlation between TM pigmentation and AHO, the degree of clinical benefit would likely be limited given the high individual variability found in this study. Future research using in vivo images from automated gonioscopy combined with in-vivo humour outflow angiography may be one way to further elucidate the relationship between trabecular meshwork pigment and aqueous humor outflow.3
References
- Migliazzo CV, Shaffer RN, Nykin R, Magee S. Long-term analysis of pigmentary dispersion syndrome and pigmentary glaucoma. Ophthalmology. 1986;93:1528-1536.
- Strohmaier CA, et al. Greater Outflow Facility Increase After Targeted Trabecular Bypass in Angiographically Determined Low-low Regions. Ophthalmol Glaucoma. 2023;6:570-579.
- Zimmermann JA, et al. Position of the ISTENT Inject® Trabecular Micro-Bypass System Visualized with the NIDEK GS-1 Gonioscope ‒ A Postoperative Analysis. J Clin Med. 2023;12:5171.
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