A Global Shape Index to Characterize Anterior Lamina Cribrosa Morphology and Its Determinants in Healthy Indian Eyes

Abstract

Citation: Thakku SG, Tham Y-C, Baskaran M, et al. A global shape index to characterize anterior lamina cribrosa morphology and its determinants in healthy Indian eyes. Invest Ophthalmol Vis Sci. 2015;56:3604-3614. DOI:10.1167/iovs.15-16707 PURPOSE. Lamina cribrosa (LC) morphology could be implicated in the progression of glaucoma. To date, no established, quantifiable parameter to assess LC shape in vivo exists. We aim to introduce a new global shape index for the anterior LC (LC-GSI) and to identify associations with ocular factors in a healthy Indian population. METHODS.Optical coherence tomography (OCT) scans of the optic nerve head (ONH) were performed on 162 healthy subjects. Optic nerve head structures were delineated and a geometric characterization of anterior LC morphology was obtained by measuring curvature along 180 LC cross sections and representing it as LC-GSI ranging from À1 to þ1. Lamina cribrosa depth and curvature were also reported. Linear regression was used to identify factors associated with LC morphology.RESULTS. The typical healthy LC had a saddle rut-like appearance, with a central ridge visible in superior-inferior cross sections. A more prominent central ridge (larger LC-GSI) was associated with shorter axial length (P < 0.001), smaller Bruch's membrane opening (BMO) area (P ¼ 0.020), smaller vertical cup-to-disc ratio (VCDR) (P ¼ 0.007), and larger minimum rim width (BMO-MRW) (P ¼ 0.001). A deeper LC was associated with male sex (P < 0.001), shorter axial length (P ¼ 0.003), larger VCDR (P < 0.001), and smaller BMO-MRW (P ¼ 0.002). Age and IOP were not significantly associated with LC morphology in healthy eyes.CONCLUSIONS. The LC-GSI is a single index that quantifies overall LC shape in an intuitive way. Ocular determinants of LC-GSI in healthy eyes included risk factors for glaucoma (axial length, VCDR, and BMO-MRW), highlighting the potential role of LC morphological characterization in the diagnosis and monitoring of glaucoma.Keywords: lamina cribrosa morphology, optic nerve head, optical coherence tomography A major site of retinal ganglion cell (RGC) damage in glaucoma is at the optic nerve head (ONH), where RGC axons congregate before making their way to the brain. [1][2][3] Within the ONH, RGC axons pass through a mesh-like collagen fiber structure called the lamina cribrosa (LC), before exiting the eye.Lamina cribrosa morphology and progression of glaucoma are believed to be closely related. 4 In particular, glaucomatous onset is associated with posterior displacement of the anterior LC surface, 5-7 posterior migration of the LC insertion points, 6 and backward bowing of the entire LC. 8 Nonhuman primate models of glaucoma have also shown similar associations. 9-11Furthermore, these models suggest that LC changes precede surface level retinal nerve fiber layer (RNFL) thinning, 11,12 which is a useful marker of glaucoma onset. Taken together, these findings indicate that an assessment of LC morphology may potentially be used as a biomarker for early glaucoma detection. The...

Shape Changes of the Anterior Lamina Cribrosa in Normal, Ocular Hypertensive, and Glaucomatous Eyes Following Acute Intraocular Pressure Elevation

“…[21][22][23] For each eye, postprocessed OCT volumes were then delineated by a single grader (TAT) using custom-written Matlab (MathWorks, Inc., Natick, MA, USA) algorithms, as previously described. 20 Specifically, the anterior LC and BMO were manually delineated. The position of the anterior LC was defined by a sharp increase in axial signal intensity (corresponding to collagen) extending laterally up to the LC insertion points in the peripapillary sclera.…”

“…This error was measured at approximately 9 lm, which is approximately twice the axial resolution of the OCT scans (4 lm). 20 We reconstructed the ONH structures in 3D, and our customized Matlab algorithms automatically derived the LC-GSI and the LC depth according to established protocols and as described below. 20 Protocol 1: Lamina Cribrosa-Global Shape Index.…”

“…For each radial cross-section, a circular arc was fit to each LC curve as in our previous publication. 20 Figure 2 illustrates various simulated shapes that could be obtained with GSI, and the most common shape of LC in healthy eyes was a saddle rut.…”

“…Recently, our group introduced a new morphologic measure, the LC global shape index (GSI). 20 This index characterizes the geometrical shape of the anterior LC surface iovs.arvojournals.org j ISSN: 1552-5783 as a whole from a three-dimensional (3D) ONH reconstruction, and it does not depend on a reference plane (i.e., it is not dependent on reference to the BMO plane). Moreover, because the quantitative score is a single metric, it is easy to understand and compare among different disease classifications.…”

“…Our technique allows us to estimate LC shape as a whole without compromising robustness. We derived the root-mean-square error for the intraobserver variability in measurements of LC morphology from our previous publication 20 and root-meansquare error was 8.9 lm for LC depth and 0.05 for LC-GSI. …”