Understanding keratoconus: what have we learned from the New Zealand perspective?

Although first described more than 150 years ago, keratoconus is still an enigmatic disease that remains an area of wide-ranging, dynamic, international research. This review considers data from New Zealand/Aotearoa, where keratoconus is both relatively common and extensively studied. New Zealand researchers have made several significant contributions to the international literature in this field, including identifying a higher prevalence of keratoconus in New Zealand per se and within Maori and Polynesian populations compared to many international studies. As reported in other studies, a higher proportion of asthma, allergy and eczema as potential risk co-factors are present in New Zealand subjects with keratoconus compared with estimates from the general population. The rates of family history of keratoconus are typically higher than those reported internationally, with higher rates in Asian, Pacific and Maori ethnicities. Interestingly, such a positive family history has been associated with less severe keratoconus on computerised topographic analysis. Investigations of corneal microstructure have revealed dramatic alterations in the keratoconic cornea, with reduced density and abnormal morphology of the corneal sub-basal nerve plexus and decreased keratocytic density. Laboratory studies of keratoconic corneal buttons have also furthered our understanding of the pathophysiology of this disease, demonstrating elevated levels of cathepsin enzymes and localised disruptions in Bowman's layer with incursion of cellular processes from anterior keratocytes. Over the past two decades keratoconus has consistently remained the leading indication for corneal transplantation in New Zealand, accounting for over 40 per cent of cases. Indeed, New Zealand appears to have the highest reported proportion of transplantation surgery for keratoconus worldwide. Current and future studies of keratoconus in New Zealand highlight an emphasis on elucidating the genetics of, and investigating novel therapeutic interventions for, this relatively common corneal disease.