An investigation of non-invasive tear break up time and tear meniscus height of keratoconic versus non-keratoconic individuals

Abstract

Keratoconus is a debilitating condition where the cornea develops a conical shape rather than the characteristic round shape due to various physiological and structural changes taking place within the layers of the cornea. As a result of the pathogenesis of keratoconus, there are numerous changes that may occur within the tears of these patients. Research has shown changes in the tear metabolome, the presence of degradation products as well as loss of goblet cells into the tears. Could the changes occurring within the tear structure of these patients affect the results of various tear quantity and quality tests? Non-invasive tear break up time (NTBUT) is a diagnostic test used to determine the quality of the tear film and has been used extensively when diagnosing dry eye disease. This test is utilised in order to determine the time taken for the tear film to begin breaking apart, signalling thinning of the tears. Shorter break up times are therefore indicative of instability or changes occurring within the tear film which could be diagnostic of dry eye disease. Tear meniscus height (TMH) measurements have also been utilised in clinical practice, where these measurements provide an indication of the volume of tears contained within the upper and lower menisci. Lower tear volumes have been shown to be present in cases of dry eye disease where either tear production or tear drainage may be affected. Changes in the quality and quantity of the tear film in subjects with dry eye disease have been thoroughly investigated; however, the same cannot be said for subjects with keratoconus. Could the same findings be possible in subjects with keratoconus? Is it possible that the changes occurring within the tears of keratoconic subjects could lead to abnormal NTBUT and TMH measurements when compared to those of control subjects? Could the results of the NTBUT and TMH tests be related to one another? This study compares the NTBUT and TMH measurements of both keratoconic and control subjects by making use of a single type of instrumentation, namely the Oculus Keratograph 4 (OK4). The results of this study reveal that the values obtained for each of the two subject groups are not shown to be statistically significantly different and that there is no significant correlation between the NTBUT and TMH measurements when comparing keratoconic and control subjects.