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Alan D. Springer, Julia E. Reid, Gerald W. Zaidman; Effect Of Removing Retinal Curvature And Tilt With Finite Element Analysis On OCT Retinal Thickness Values. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1330.
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To determine whether removing retinal curvature and tilt enhances the ability to detect retinal thickness differences in OCT scans of normal and myopic eyes.
Volunteers had their retinas scanned with a Cirrus-HD OCT. A horizontal section through the fovea was selected and finite element analysis (FEA) models were created using the inner limiting membrane (ILM) and retinal pigment epithelium (RPE) lines as model boundaries. The FEA retinal models were relaxed virtually, to convert the curved RPE line into a straight line. Thereby, curvature and tilt were eliminated. Thereafter, retinal thickness was measured at 5 eccentricities: the fovea, nasal and temporal rims and at points mid-way between each rim and the corresponding edge of the scan. These FEA measurements were compared with those generated by the Cirrus software. Other retinal features, such as tilt, retinal curvature and foveal radius of curvature (ROC) were also quantified, and these parameters were evaluated with respect to degree of myopia.
A multifactor ANOVA found neither a significant difference between Cirrus and FEA thickness values nor an eccentricity x Cirrus/FEA interaction. An eccentricity effect was observed and was due to the nasal (N) rim being significantly thicker than the temporal (T) rim (P<0.02). Thickness at the N and T rims was negatively correlated (-0.97; P<0.003) with the degree of retinal curvature, and the latter was negatively correlated with magnitude of myopia (-0.86; P<0.03), indicating that myopia is associated with more retinal curvature and thinner retinal rims. Foveal pit width and foveal ROC also increase with myopia by 24% and 58%, respectively.
Cirrus thickness values are reliable, independent of retinal tilt and retinal curvature. However, eliminating retinal tilt and curvature reduces between-subject variability and allows obtaining significant results with fewer subjects. Myopia is significantly associated with reduced retinal tilt, increased retinal curvature, thinner retinal rims, wider pits, and increased foveal ROC. The results suggest that retinal stretching in myopes leads to progressively thinner retina and wider pits. The reduction of retinal thickness at the rims may be related to inner retinal cell loss.
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