Corneal structure and biomechanics: relationship to diagnosis and treatment of glaucoma and keratoconus

This thesis extensively investigates the relationship of corneal structure and biomechanical profile to the diagnosis and treatment of two ocular disorders: glaucoma and keratoconus. The research papers arising out of these studies have been compiled to form this thesis by publication. The main hypotheses addressed by this PhD thesis include: 1. Baseline central corneal thickness could be a predictive factor of glaucoma progression 2. Ongoing change in corneal thickness may occur in glaucoma subjects and this might be related to glaucoma progression. 3. Altering the dynamic properties of the cornea by collagen crosslinking can affect the progression of disease in keratoconic subjects. Despite having different mechanisms, both conditions are significant causes of preventable blindness. Glaucoma is more prevelant in the older population whereas keratoconus tends to affect younger subjects. Interestingly, thinner corneas and altered biomechanics are related to glaucoma risk and also characteristic of keratoconus. The aim of the glaucoma studies was to identify longitudinal variation in corneal thickness and its relationship to antiglaucoma medications and visual field progression. This could provide some insight on the clinical relevance of repeat corneal thickness measurements in glaucoma practice. Our findings indicate that corneal thickness reduces slightly over time in eyes on topical prostaglandin therapy and that thinner corneas may be associated with an increased risk of visual field progression. The keratoconus studies aimed to explore the relationship between corneal structural and biomechanical characteristics, compare corneal imaging devices, analyse the sensitivity and specificity of biomechanical parameters in keratoconus detection and study the outcome of collagen crosslinking in adult and paediatric progressive keratoconic eyes. Knowledge from these studies would allow clinicians to identify and manage keratoconus more efficiently. Our results indicate significant correlations between corneal structural and biomechanical characteristics. We also demonstrated that some commercially available corneal imaging devices are not interchangeable in clinical practice and that newer biomechanical parameters are sensitive in detecting corneal ectasia. Furthermore, we validated the efficacy of the corneal collagen crosslinking procedure in adult and paediatric progressive keratoconic eyes.