The Shape of Posterior Sclera as a Biometric Signature in Open-angle Glaucoma: An Intereye Comparison Study

Abstract

Purpose: To characterize intereye differences in posterior segment parameters and determine their significance in open-angle glaucoma patients with unilateral damage.

Methods: Both eyes from 65 subjects without any nerve damage and 43 patients undergoing treatment for unilateral open-angle glaucoma were included in this study. A 12.0×9.0×2.6 mm volume of the posterior segment in each eye was scanned with swept-source optical coherence tomography. Coronally reconstructed optical coherence tomography images were analyzed to determine the deepest point of the eye (DPE), which we then calculated the distance (Disc-DPE distance), depth (Disc-DPE depth), angle (Disc-DPE angle) from the optic disc center to the DPE. Posterior pole shape was analyzed measuring the posterior pole-cross-sectional area, posterior pole-horizontal width (PP-HW), and posterior pole-vertical width) of the posterior pole. These measurements and their intereye absolute difference (IAD; absolute difference in measurements between the right and left eyes) values were compared between the healthy and unilateral glaucomatous patients.

Results: The posterior sclera measurements, including the Disc-DPE distance, Disc-DPE depth, and posterior pole-cross-sectional area, were significantly different between the unilateral glaucoma eyes and contralateral healthy eyes (P=0.043, P=0.035, and P=0.049, respectively). By contrast, none of the intereye differences in optic nerve head parameters were significant in the unilateral glaucoma patients. In comparison with the IAD values, the baseline intraocular pressure and PP-HW of the posterior segment showed significant differences between the healthy and the unilateral glaucoma patients (P=0.019 and P=0.036, respectively). A multivariate analysis showed that a larger baseline intraocular pressure IAD [odds ratio (OR), 1.381; P=0.009)] and larger PP-HW IAD (OR, 1.324; P=0.032) were significantly associated with the presence of glaucoma.

Conclusions: Compared with the fellow healthy eyes, glaucomatous eyes had larger and more steeply curved posterior poles, which represent a structural variation of the posterior sclera that might be associated with glaucomatous optic neuropathy.

FIGURE 1

Deepest point of the eye (DPE) and measurement landmarks in the reconstructed coronal scan. Bruch’s membrane (BM) seemed as a hyper-reflective round plane with no hyporeflective vitreous cavity inside BM, and with the nonhomogenous hyporeflective choroid surrounding the outside of the BM. This landmark is designated as the DPE (A). The Disc-DPE distance (A) was quantified as the lineal distance from the optic disc center to the DPE measured along the same en-face image as the DPE. The Disc-DPE depth (B, C) was calculated by counting the number of coronal sections from the interface of the DPE to the interface of the optic disc center.

FIGURE 2

The shape and curvature of the posterior segment was represented using the biometric measurements obtained at the center of the optic disc in the reconstructed coronal section. Posterior pole-cross-sectional area (PP-CSA) was the total cross-sectional area of the vitreous cavity measured at the height of the optic disc (A). The posterior pole-horizontal width (PP-HW) was the horizontal width of the vitreous cavity, measured at the height of the optic disc (B). The posterior pole-vertical width (PP-VW) was the vertical width of the vitreous cavity measured at the height of the optic disc (C).

FIGURE 3

Representative case of characteristic posterior sclera shape of the glaucomatous right eye (A–C) and the healthy left eye (D–F) of a same patient. Larger posterior pole-horizontal width was a distinct feature. Red arrow designate the larger PP-HW in the glaucomatous right eye and the blue arrow designate the smaller PP-HW in the healthy left eye. I indicates inferior; N, nasal; S, superior; T, temporal.