Analyses of shape of eyes and structure of optic nerves in eyes with tilted disc syndrome by swept-source optical coherence tomography and three-dimensional magnetic resonance imaging

Abstract

Purpose: To evaluate the deeper structures of the optic nerve and to analyze the shape of eyes with tilted disc syndrome (TDS) by swept-source optical coherence tomography (OCT) and three-dimensional magnetic resonance imaging (3D MRI).

Methods: The medical records of 54 eyes of 36 patients with TDS were reviewed. The patients with TDS and high myopia were analyzed separately from those without high myopia. All the eyes were examined with a swept-source OCT, and 22 of the eyes were examined by 3D MRI.

Results: A total of 38 eyes of 29 patients were highly myopic and 16 eyes of 15 patients were not highly myopic. The representative OCT findings of the optic disc were: a sloping of the lamina cribrosa posteriorly from the upper part to the lower part, a protrusion of the upper edge of Bruch's membrane, and choroid. The distance and the depth of the most protruded point from the fovea were significantly greater in the eyes with non-highly myopic TDS than those with highly myopic TDS. In the 3D MRI, the lower part of the posterior segment was protruded outward, and the optic nerves attached at the upper nasal edge of the protrusion.

Conclusions: The abnormalities detected by swept-source OCT and 3D MRI analyses indicate the possibility that the essential pathology of TDS is a deformity of the inferior globe below the optic nerve, and the positional relation between the fovea and the inferior protrusion determines the degree of myopia.

Figure 1

Fundus photographs and swept-source OCT images showing the characteristics of the OCT findings of the optic disc in the eyes with TDS. (a) Fundus photograph of the right eye of a 58-year-old woman with a refractive error (spherical equivalent) of −5.0 diopters and axial length of 26.3 mm. The optic disc is tilted inferiorly, and an inferior conus is present. The fundus inferior to the optic disc is tessellated. The OCT scan direction for Figure 1b is shown as a white line with arrowhead. (b) Vertical OCT image recorded along the white scan line in Figure 1a. The inner surface of the lamina cribrosa has a clear change of reflectance (arrowheads). The lamina is sloped posteriorly from the upper part to the lower part. (c) Fundus photograph of the right eye of a 60-year-old woman with a refractive error (spherical equivalent) of −12.5 diopters and axial length of 28.7 mm. The optic disc is tilted and a conus is present inferotemporal to the optic disc. The OCT scan direction for Figure 1d is shown as white line with arrowhead. (d) Vertical OCT image along the white line in Figure 1c. The Bruch's membrane-choroid complex is protruded (arrow) toward the optic disc area along the upper margin of the disc. The nerve tissue is herniated into the protruded Bruch's membrane-choroid complex and bent superiorly (arrowheads) beyond the upper margin of the optic disc. (e) Fundus photograph of the right eye of a 67-year-old woman with an axial length of 25.9 mm. The optic disc is tilted inferiorly. The OCT scan direction for Figure 1f is shown as white line with arrowhead. (f) Vertical OCT image across the optic disc showing that the retinal nerve fiber tissue is elevated (arrowheads) along the upper border of the optic disc. (g) Fundus photograph of the left eye of a 58-year-old woman with a refractive error (spherical equivalent) of −6.5 diopters and axial length of 27.1 mm. The optic disc is tilted and an inferior conus is present. The OCT scan direction for Figure 1h is shown as white line with arrowhead. (h) Vertical OCT image showing the presence of ICC (white line with arrowhead) inferior to the tilted optic disc. Scale bars=1 mm.

Figure 2

Spatial relationship between the attachment site of the optic nerve and the entire eye based on 3D MR images of eyes with and without TDS. (a, b) Nasal view (a) and posterior view (b) of an emmetropic eye. The axial length of the eye is 23.8 mm. The shape of the posterior segment of the eyes is symmetrically hemispheric. The attachment site of the optic nerve is slightly nasal from the center of the posterior segment (b, arrow), and the optic nerve is attached perpendicularly to the globe (a). The curvature of the attachment site of the optic nerve is vertically straight when the globe is viewed from the nasal side (a). (c, d) Nasal (c) and posterior (d) views of a highly myopic eye without TDS. Axial length of the eye is 29.9 mm. The eye is elongated in anterior–posterior direction and a posterior protrusion exists along with the visual axis (c). The attachment site of the optic nerve is in the middle of the protrusion (c, d arrow), and the optic nerve is attached perpendicularly to the globe (c). The curvature of the attachment site of the optic nerve is vertically straight when the globe is viewed from the nasal side (c). The lower boundary of the posterior protrusion can be clearly seen (d). (e, f) Nasal (e) and posterior (f) views of an emmetropic eye with TDS. Axial length of the eye is 23.7 mm. The lower half of the globe has a completely different curvature from the upper half of the eye (e). The expansion of lower globe is wide and the lower boundary of the inferior staphyloma is not obvious (f). The optic nerve is attached along the upper edge of posterior protrusion and the curvature of the attachment site of the optic nerve is oblique when the globe is viewed from the nasal side (e, f arrow). N, nasal; T, temporal.