The lamina cribrosa represents an important site for axonal injury in glaucoma. Glaucomatous excavation of the optic nerve head is related to posterior bowing and collapse of the lamina cribrosa which is believed to impede axoplasmic flow and contribute to loss of neuronal functional and subsequent axonal death. Recent advancements in OCT technology using enhanced depth imaging (EDI) has enabled direct in-vivo visualization of the lamina and demonstrated various anatomic changes including laminar thinning, posterior migration into the sclera, loss of laminar beams, and focal disinsertion from the scleral rim. These findings not only provide critical insight regarding glaucoma pathogenesis, but also represent an opportunity for new therapeutic targets.
In the present study, Lee and colleagues examined the optic discs of 137 glaucomatous eyes using EDI and evaluated three-dimensional scans reconstructed from B-scan images. Quantitative and qualitative assessments of the lamina cribrosa were generated using novel rendering techniques. Considerable variability in laminar shape and configuration was observed, and a high level of interobserver and intersession reproducibility was measured using both techniques. The anatomy of the laminar cribrosa is complex and the mechanism by which neuronal damage may occur at the level of the lamina is multifactorial. Deformation of the lamina may produce direct compression of axonal bundles within the laminar pores, changes in axoplasmic flow with neurotrophin deficiency, and alterations in axonal perfusion by compression of blood vessels. In addition, the lamina represents the interface between the intraocular pressure (IOP) and intracranial pressure (ICP). Dynamic changes in IOP, ICP, and systemic blood pressure may alter the configuration of the lamina and optic nerve head anatomy and need to be carefully considered when interpreting EDI scans.
Novel therapeutic targets may one day be directed at the lamina to provide increased structural support to axons passing through the lamina pores
As emphasized in this well designed and executed study, OCT assessment of the lamina cribrosa in glaucoma patients represents an emerging opportunity to examine the role of the lamina in the onset and progression of glaucomatous optic neuropathy. Novel therapeutic targets may one day be directed at the lamina to provide increased structural support to axons passing through the lamina pores.