The validity of corneal confocal microscopy (CCM) in assessing peripheral neuropathy has been studied extensively in several studies with a large cohort of subjects with diabetes and in a handful of studies with small sample sizes in subjects with other systemic conditions. The non-invasive nature of this technique as well as its high reproducibility, moderate to high sensitivity and specificity, and ease of use make it an ideal biomarker for diagnosing onset, severity and progression of peripheral neuropathy. This thesis aims to further investigate the potential of CCM by evaluating abnormalities in the corneal sub-basal nerve plexus, Langerhans Cells (LCs) and epithelial cells in neuropathy related to diabetes and cancer. This thesis has established that evaluating the sub-basal nerve plexus in the centre and at the inferior whorl increases the diagnostic performance of CCM. In addition to diagnosing clinical and subclinical neuropathy in children and adults with diabetes CCM can also identify sub-clinical nerve damage in patients with upper gastrointestinal cancer and assess the effects of chemotherapy. CCM also identifies differences in small fibre pathology between diabetic patients with and without painful neuropathy. Although there was an increased prevalence and severity of dry eye and LCs' density, this was not related to an abnormality of corneal nerves in diabetic patients with no or mild neuropathy. Epithelial cell morphology was not associated with corneal nerve damage and did not alter in patients with Type 1 diabetes. In conclusion, CCM has been shown to be an ideal marker for quantifying early small fibre pathology and assessing peripheral neuropathies.