The use of 1050nm OCT to identify changes in optic nerve head pathophysiology in glaucoma

Glaucoma is a progressive optic neuropathy that causes irreversible vision loss and is the second leading cause of blindness worldwide. Glaucoma is characterised by loss of retinal ganglion cells (RGC) and the proposed site of primary damage is the lamina cribrosa (LC), where RGC axonal transport is disrupted causing subsequent RGC damage and eventual cell death. Current detection for primary open angle glaucoma (POAG) is based upon clinical measures such as intraocular pressure (IOP), visual field loss and changes to the optic nerve head (ONH). However, for there to be an indication that there is a problem using these measures, often RGC damage has already occurred. Therefore it is crucial to determine ocular parameters that alter in the earliest stage of disease, prior to vision loss occurring. In this thesis optical coherence tomography (OCT) was used to assess the optic nerve heads and maculae of control eyes and eyes with preperimetric, early and advanced glaucoma in order to characterise changes that could potentially be used as biomarkers for the earliest stages of the disease. A custom built 1050 nm research OCT was used to acquire datasets from the macula and optic nerve heads of eyes glaucomatous and control eyes in vivo. Analysis of the inner retinal layers at the macula was performed to indirectly assess RGC integrity. At the ONH the prelamina and LC volume and regional depth and thicknesses were investigated. Additionally, nerve fibre layer and Bruch’s membrane parameters were assessed. Finally, LC beam coherence and orientation were probed in order to determine whether regional or glaucomatous changes ould be detected at the LC connective tissue microstructure. Prelamina depth and thickness was shown to be an indicator of early and preperimetric glaucoma (p 0.01). Border nerve fibre layer revealed significant thinning in early glaucoma compared to control, and the superior peripapillary nerve fibre layer was thinner in preperimetric glaucoma than control. The ratio of inner plexiform layer (IPL) : ganglion cell layer (GCL) showed significant differences between control eyes and preperimetric glaucoma, and as such has potential to be a useful biomarker for indicating the earliest stages of disease. Both the GCL and IPL were thinner in early glaucoma than control (p<0.01), a hypothesis that cell body shrinkage and death occurs in preperimetric glaucoma and dendritic loss occurs in early glaucoma, when vision loss is first apparent, is suggested. Additionally, LC beams showed greater coherence in the superior and inferior poles than the temporal region, indicating that the shows regional variation but that further research is required to characterise changes. In conclusion, 1050 nm OCT was used to probe microstructural parameters of the optic nerve head in vivo to characterise changes that could be used as a potential biomarker for early glaucoma. ONH and retinal parameters have been identified that, with further research, may be used to differentiate between control eyes and those with preperimetric and early glaucoma. These have the potential to help identify those ONHs at risk of glaucoma damage.