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Oculus

Editors Selection IGR 23-1

Clinical Examination Methods: Pulsatile Trabecular Motion and IOP Fluctuations

Michael Girard

Comment by Michael Girard on:

100738 Pulsatile Trabecular Meshwork Motion: An Indicator of Intraocular Pressure Control in Primary Open-Angle Glaucoma, Du R; Xin C; Xu J et al., Journal of clinical medicine, 2022; 11:

See also comment(s) by Clemens Strohmaier & Alex Huang


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In the proposed study, the authors suggest that if one could fully characterize the biomechanical behavior of the trabecular meshwork (TM), one could potentially predict future IOP fluctuations in individual patients. After all, the TM plays a major role in the control of IOP, and such a knowledge could have implication for the management of glaucoma. Specifically, in this study, the authors were able to dynamically map the deformations of the TM in response to a change in IOP during the cardiac cycle (also known as the ocular pulse). Those systole-to-diastole deformations are pulsatile in nature, and were locally mapped using phase-contrast optical coherence tomography (OCT), following a protocol already established by the same authors.1

To test their main hypothesis, the authors recruited 20 normal and 30 glaucoma subjects. All subjects underwent biomechanical mapping (to assess diastole-to-systole TM movement). The authors found that the TM of glaucoma eyes exhibited less TM displacement (and at a lower velocity) in response to the ocular pulse. Regional variations were also observed in both groups. When glaucoma groups were further divided into two (according to their maximum diurnal IOP fluctuations; of less or more than 8 mmHg), the group that exhibited the highest diurnal IOP fluctuations also exhibited the least TM displacements and velocities (nasal quadrant only). In other words, knowledge about TM biomechanics might tell us which patients would be more likely to exhibit transient IOP fluctuations.

Knowledge about TM biomechanics might tell us which patients would be more likely to exhibit transient IOP fluctuations

The proposed work has merit and several aspects can be discussed here for future improvements. First, TM displacement is not necessarily directly related to TM stiffness. TM displacement will be affected by the magnitude of the applied loads (including the ocular pulse) but also by surrounding tissues. For instance, the ocular pulse has been found to be different between normal and glaucoma patients. The ocular pulse is highly affected by a change in corneo-scleral stiffness, baseline IOP value, or in the choroidal pulse volume, all of which are known to change with the development and progression of glaucoma. Such variables would need to be very well controlled in future work. Second, TM stiffness can be assessed using techniques such as the 'inverse finite element'.1 Such methods could complement the proposed analyses. Third, to gain a comprehensive knowledge of TM biomechanics, diastole-to-systole TM displacements should also be reported as full 3D vector fields. This is currently a technology limitation. Finally, to interpret their clinical data, it is worth noting that the authors would highly benefit from the use of a mathematical model that would model the biomechanics of drainage up to the episcleral vein. The authors have already conceptualized many aspects of the problem.2

References

  1. Wang K, Johnstone MA, Xin C et al. Estimating Human Trabecular Meshwork Stiffness by Numerical Modeling and Advanced OCT Imaging. Invest Opthalmol Vis Sci. 2017;58:4809-4817.
  2. Johnstone M, Xin C, Tan J, et al. Aqueous outflow regulation ‐ 21st century concepts. Prog Retin Eye Res. 2020;83:100917.


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