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HaagStreit

Editors Selection IGR 20-4

Anatomical Structures: See the trabeculum!

Alex Huang
Jong Yeon Lee

Comment by Alex Huang & Jong Yeon Lee on:

82570 High-Resolution, Adaptive Optics Imaging of the Human Trabecular Meshwork In Vivo, King BJ; Burns SA; Sapoznik KA et al., Translational vision science & technology, 2019; 8: 5


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In this study, the authors describe proof-of-concept in-vivo human trabecular meshwork (TM) imaging using high-resolution adaptive optics gonioscopy (AOG). AOG can visualize TM beams and presumed TM endothelial cells. They compared the TM appearance between control and pigment dispersion syndrome patients. Diminished spacing between the beams and enlarged endothelial cells with hyper-reflective foci were observed in pigment dispersion syndrome TM.

In-vivo TM micrometer-level imaging using AOG has several advantages. For example, subtle differences in TM morphology were seen comparing AOG, scanning electron microscopy (SEM),1 and in situ human two-photon imaging.2 AOG likely gives a more representative description because it avoids tissue-preparation and fixation-associated artifacts. Also, as AOG is non-invasive, AOG allows for longitudinal patient assessment. Investigators can now study TM age-related changes and the impact of TM-based glaucoma treatments (medications, lasers, or TM-targeted minimally invasive glaucoma surgeries).

Performing in vivo TM imaging with segmental information (such as from aqueous angiography) could yield additional insight into TM biology and potentially lead to novel outflow-based glaucoma therapies

However, several limitations exist. First, AOG cannot query deeper TM structures such as the juxtacanalicular meshwork or Schlemm's canal, which are important parts of aqueous humor outflow resistance. This challenge may be overcome by using longer wavelength lasers.

Additionally, the new concept of segmental aqueous humor outflow is important here. Aqueous angiography has shown the segmental outflow in living non-human primates and humans.3,4 Different AOG results could have been obtained depending on the location of the test (high-flow vs. low-flow TM). Therefore, performing in vivo TM imaging with segmental information (such as from aqueous angiography) could yield additional insight into TM biology and potentially lead to novel outflow-based glaucoma therapies.

References

  1. Gierek A, Sosnierz M, Bialas B, Szymanski A. Morphological picture of the iridocorneal angle of the human eyeball viewed under a scanning electron microscope Ophthalmologica. 1974;169(5):371-376.
  2. Huang AS, Gonzalez JM, Le PV, Heur M, and Tan JC. Sources of Structural Autofluorescence in the Human Trabecular Meshwork. IOVS 2013;54(7):4813-4820.
  3. Huang AS, Li M, Yang D, et al. Aqueous Angiography in Living Nonhuman Primates Shows Segmental, Pulsa-tile, and Dynamic Angiographic Aqueous Humor Outflow. Ophthalmology 2017;124(6):793-803.
  4. Huang AS, Camp A, Xu BY, et al. Aqueous Angiography: Aqueous Humor Outflow Imaging in Live Human Subjects. Ophthalmology 2017;124(8):1249-1251.


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