Recent advances in OCT imaging of the lamina cribrosa

Abstract

The lamina cribrosa (LC) is believed to be the site of injury to retinal ganglion cell axons in glaucoma. The ability to visualise this structure has the potential to help increase our understanding of the disease and be useful in the early detection of glaucoma. While for many years the research on the LC was essentially dependent on histology and modelling, a number of recent advances in optical coherence tomography (OCT) have dramatically improved the ability to visualise the LC, such that it is now possible to image the LC in vivo in humans and animals. In this review, we highlight recent advances in OCT imaging of the LC, in the technology, processing and analysis, and discuss the impact that these will have on the ability to diagnose and monitor glaucoma, as well as to expand our understanding of its pathophysiology. With this manuscript, we aspire to share our excitement on the achievements and potential of recent developments as well as advise caution regarding the challenges that remain before imaging of the LC and optic nerve can be used routinely in clinical practice.

Keywords: Anatomy; Glaucoma; Imaging; Intraocular Pressure; Optic Nerve.

Figure 1

Swept source optical coherence tomography (SS-OCT) for assessing the lamina cribrosa (LC) defects. (A) Colour disc photograph shows orientations of the SS-OCT scan. (B) B-scan image averaging multi-scan frames at green line in (A), with the anterior (red dots) and posterior border (green dots) of the LC delineated. The LC pores are also visualised as hyporeflective lines in LC. (C) The SS-OCT C-mode image reconstructed from raster scan. The laminar pores are visualised as hyporeflective spots on the en face image. The LC defects are shown by green arrowheads as hyporeflective lesions. (D) The SS-OCT sectioned volume image oriented by white line in (A). The LC defects are shown by green arrowheads as a hyporeflective line, which shows full-thickness loss of the lamina reflectivity on B-scan image.

Figure 2

Adaptive optics optical coherence tomography (AO-OCT) for assessing lamina cribrosa (LC) microarchitecture. (A) C-mode section at the level of the LC through an AO-OCT scan of a glaucomatous eye acquired in vivo. (B) The beams (cyan) and pores (green) were identified using a semiautomated segmentation technique. (C) 3D structural view of LC beams; (D) 3D LC beam thickness was then measured at every voxel, where hotter colours represent thicker beams. Adapted with permission from Nadler et al.

Figure 3

Effects of intraocular pressure (IOP) increase on non-human primates. (A and B) The acute effects of (A) 10 mm Hg (top) and (B) 45 mm Hg (bottom) IOP on spectral domain optical coherence tomography (SD-OCT) B-scans of a normal monkey eye. Bruch's membrane (red dots) and the anterior lamina cribrosa (LC) surface (green dots) have been delineated. The area enclosed by the anterior surface of the LC and a plane defined at Bruch's membrane opening (area shaded green) is larger in the scan at 45 mm Hg. There was no detectable lateral expansion of the scleral canal at Bruch's membrane opening (vertical green lines). Using a second reference plane parallel to BM opening (dashed red lines), it is also visible that the BM is outwardly bowed at high IOP, which suggests that there is IOP-induced posterior deformation of the peripapillary sclera. While choroidal compression may contribute to this finding, we believe that the behaviour of BM is principally related to the behaviour of the sclera. (C) The chronic effects of IOP elevation on the morphology and position of the internal limiting membrane and anterior surface of the LC are compared in an early glaucoma monkey eye. (D) Anterior LC surface and neural canal opening at baseline (green), follow-up 1 (yellow) and follow-up 2 (red). Delineations were made on images acquired with SD-OCT. Adapted with permission from Sigal et al and Strouthidis et al.

Figure 4

Adaptive compensation for lamina cribrosa (LC) imaging. Baseline optical coherence tomography (OCT) images of two healthy patients and their enhanced versions using adaptive compensation to correct the effects of light attenuation. In the baseline images, arrows indicate poor visibility of the LC (red) and of the peripapillary sclera (blue). Adaptive compensation, when applied as a postprocessing treatment, allows recovery of the LC and peripapillary sclera even in cases where OCT signal is barely visible in the original images (left). Note that for the left image, the entire LC cannot be recovered. Adapted with permission from Mari et al.

Figure 5

3D deformation tracking. Results from tracking analysis to determine the 3D displacement in response to the change in intraocular pressure (IOP) caused by IOP-lowering trabeculectomy in a glaucoma subject. Adapted with permission from Girard et al.