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Anse Vellappally, Yoav Glidai, Palaiologos Alexopoulos, Mengling Liu, Ian A. Sigal, Matthew A. Smith, Joel Schuman, Hiroshi Ishikawa, Gadi Wollstein; Depth-wise lamina cribrosa deformation while modulating intracerebral pressure. Invest. Ophthalmol. Vis. Sci. 2021;62(11):74.
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Previous research by our group has shown that both intraocular pressure (IOP) and intracerebral pressure (ICP) modulation have an important role in deformation of the lamina cribrosa (LC). Considering that these forces are acting in different locations and direction (IOP -anterior posterior, ICP -circumferential) it is important to determine the effect and primary location of each of these forces. In this project we examine the deformation of the LC in response to ICP modulation while maintaining a fixed IOP.
Six eyes of 5 healthy adult rhesus macaques (3 males and 2 females, aged 7.9-14.4 years) were used in the study. The anterior chamber of the eye and the lateral ventricle of the brain were cannulated and the pressure was modulated through gravity-based perfusion system. In-vivo optic nerve head (ONH) spectral-domain OCT scans (Leica, Chicago, IL) were obtained at a fixed IOP of 15mmHg and 3 ICP settings: baseline, 20 and 35mmHg. Qualified scans were registered in 3D, and LC microstructure measurement of the beam-to-pore ratio (BPR) was obtained from shared regions and depths using a previously described segmentation algorithm.
The pattern, magnitude and location of LC deformation markedly varied between eyes in response to ICP modulation (Figure). Eyes were grouped based on the SD of the difference in BPR in the varying pressure settings with eyes > 0.11 defined as deforming and those equal or lower defined as non-deformer (Table). Three deforming eyes exhibited BPR change in different locations within the LC depth (Figure, A-C), whereas the remaining three showed only minimal response (Figure, D-F). The baseline mean BPR was 1.63 for the deforming eyes and 1.39 for the non-deforming eyes. The mean depth-wise, slice-by-slice BPR difference between the pressure settings in the 3 deforming eyes (A-C) was 0.58±0.43 (range 0.29-1.08), and 0.14±0.03 (range 0.11-0.17) in the non-deforming eyes (D-F).
Under raised ICP levels and fixed IOP, the LC showed inconsistent pattern of deformation along its depth among the different eyes. It is highlighting the importance of analyzing the full depth of the LC in order to fully capture the pressure effects. Eyes with larger beams (or smaller pores) tend to be more resistant to the ICP pressure modulation. The association between the LC response to pressure modulation and sensitivity to glaucomatous damage require further investigation.
This is a 2021 Imaging in the Eye Conference abstract.
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