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Editors Selection IGR 19-3
Anatomical Structures: Lamina Cribrosa Mechanics in an Animal Model
Comment by Andrew Tatham on:
65845 Phase-contrast Micro-computed Tomography Measurements of the Intraocular Pressure-induced Deformation of the Porcine Lamina Cribrosa, Coudrillier B; Geraldes D; Vo N et al., IEEE Transactions on Medical Imaging, 2016; 35: 988-999
Intraocular pressure (IOP)-induced deformation of the lamina cribrosa (LC) is believed to be an important mechanism of retinal ganglion cell axonal damage in glaucoma. It is possible to obtain in vivo images of the LC using enhanced depth- or swept-source-OCT, however, the resolution of OCT is limited and it is not always possible to visualize the entire LC due to problems of tissue shadowing and limited light penetration.
X-ray-based imaging provides an alternative method of assessing the LC in the laboratory but also has limitations, particularly as neural tissue and LC collagenous beams have similar X-ray attenuation properties. Researchers have attempted to better differentiate collagen and neural tissue using tissue dyes but application of dyes affects stiffness of the tissue, introducing a potentially important confounding factor in studies of optic nerve head biomechanics.
This paper describes the first use of new imaging technique, known as phase contrast micro-computed tomography (PC µCT), to image the LC. The method allows imaging of soft tissues without the need for contrast agents by taking advantage of the different refractive indices of adjacent tissues, even those of similar density.
The authors demonstrate that PC µCT can be used to image the fine structures of the LC and evaluate structural changes that occur in response to IOP elevation. The study involved mounting porcine eyes in a pressure chamber, with pressure adjusted between 6 mmHg and 37 mmHg. Elevated pressure was shown to result in posterior displacement of the sclera and LC, compressive deformation through the thickness of the LC and sclera, and tensile deformation along the transverse direction of the anterior LC. Certain regions of the LC were subject to considerably more compressive strain than others, being largest in the anterior central LC.
Although the study included only a small number of eyes, and the technique is not suitable in vivo, the study shows that PC µCT has the potential to further understanding of optic nerve head biomechanics.
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