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R. E. Norman, J. G. Flanagan, S. M. K. Rausch, I. A. Sigal, I. Tertinegg, A. Eilaghi, S. Portnoy, J. G. Sled, C. R. Ethier; Dimensions of the Human Sclera: Thickness Measurement and Regional Changes With Axial Length. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4899.
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© ARVO (1962-2015); The Authors (2016-present)
Scleral thickness, especially near the optic nerve head (ONH), influences ONH biomechanics and thus may be relevant to the development of glaucomatous optic neuropathy. Here we characterized the scleral thickness distribution and other geometric features of human eyes.
11 enucleated human globes (7 normal, 4 with a reported history of glaucoma) were imaged by high-field MRI (80 µm isotropic resolution). The MRI scans were segmented to produce 3-D corneoscleral shells. Each shell was divided into 15 slices along the anterior-posterior axis, and each slice was further subdivided into the anatomical quadrants. Average thickness was measured in each region, giving 60 thickness measurements/eye. Scleral geometric features were correlated with globe axial length.
Group mean thickness over the whole sclera was 670±80 µm (mean±SD). Maximum thickness occurred at the posterior pole of the eye, with mean thickness of 996±181 µm. Thickness decreased to a minimum at the equator, where a mean thickness of 491±91 µm was measured. Correlations between axial length and ONH canal diameter (r=-0.670, p=0.024), axial length and scleral thickness near the ONH (r=-0.607, p=0.048), and axial length and the ratio of posterior scleral volume to total scleral volume were found (r=-0.638, p=0.035). A trend of thinning of the posterior sclera was observed in the glaucomatous eyes (876±150 µm) relative to the normal eyes (1065±144 µm).
There is significant inter-individual variation in scleral thickness, which may result in inter-individual differences in ocular biomechanics. Several geometrical parameters of the eye, including posterior scleral thickness and volume, axial length, and ONH canal diameter, appear linked. Eyes with a reported history of glaucoma were found to have longer axial length, smaller ONH canal dimensions and thinner posterior sclera.
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