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Joel R Palko, Jun Liu; Scleral thickness measurements of fresh human globes using micro-CT. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2230.
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Dimensions of the corneoscleral shell are of interest in transscleral drug delivery and in understanding the biomechanics of the globe in myopia and glaucoma. Accurate scleral thickness measurements are necessary to determine the structural properties of the eye and are of importance for finite element analyses. Prior studies investigating fixed scleral thickness have utilized contrast-enhanced micro-MRI [Normal et al, Exp Eye Res 2010, 90(2)] and histological cross-sections [Olsen et al, Am J Ophth 1998, 125(2)]. The objective of this study was to measure the scleral thickness distribution in unfixed human globes using micro-CT.
A micro-CT scanner (Skyscan 1172, Belgium) at a voxel size of 9 µm was used to image 4 human eyes within 72 hours of enucleation. A 3 mm diameter corneal hole was used to extract the internal globe contents. The eye was sealed in a moisturizing chamber during scanning and was pressurized to approximately 10 mmHg with air using a tube system. Scleral image segmentation was completed semi-automatically use a custom Mathematica (Wolfram, Champaign, IL) program. A 3D point cloud and subsequent mesh was created for each eye. Thickness was calculated using the distance of vertex normals from the exterior scleral mesh to their intersection with the internal scleral mesh and averaged across 2 mm circumferential increments from the scleral canal opening to the limbus.
The mean thickness of the scleral shells was 704 ± 85 µm (n=4). Fig a is a representative thickness map of a left eye. Fig b shows the mean circumferential scleral thickness by quadrant starting from the scleral canal opening (slice 1) and ending at the limbus (slice 11).
The thickness profile of the scleral shell obtained using micro-CT was similar to results obtained using histology and micro-MRI. Increased scleral thickness was found in all regions compared to prior studies. The increased thickness may be related to the lack of fixation or our small sample size. The current methodology provides unfixed heterogeneous scleral thickness measurements within 3D models of individual scleral shells. Future work will utilize contrast agents to better differentiate the scleral flange and lamina cribrosa.
This is a 2020 ARVO Annual Meeting abstract.
Thickness map of a representative left eye (a). Mean scleral thickness by quadrant from peripapillary sclera (slice 1) to the limbus (slice 11) (b). N-nasal; S-superior; T-temporal; I-inferior; A-anterior; P-posterior
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