The influence of Meibomian gland morphology and function on ocular comfort

Abstract

Dry eye is a highly prevalent disease causing symptoms of discomfort that are severe and disabling for many sufferers. One of the leading causes of the evaporative form of this complaint is believed to be Meibomian Gland Dysfunction (MGD). Although clinical manifestations of MGD are easily observed, the association between the morphology and function of the meibomian gland and the symptoms experienced by those affected, remains controversial. Better understanding of this relationship may help to predict those at risk and will contribute to development of effective treatments and preventative strategies. This thesis describes a series of studies designed to investigate the relationship between subjective ocular symptomatology and both meibomian gland morphology and function. Grading scales commonly used to assess meibomian gland morphology and lid wiper epitheliopathy were validated and found to offer only moderate sensitivity to detect changes. Objective assessment systems incorporating image analysis software were developed which permitted highly repeatable and accurate assessment of meibomian gland morphology and lid wiper epitheliopathy. The Korb meibomian gland evaluator and the meibomian gland forceps were identified as the optimal meibum expression methods. Tears and meibum were collected and analysed using nano-electrospray, mass spectrometry. These techniques were able to identify and quantify the major classes of component lipids. The lipid profiles derived showed good repeatability, both within and between days. A comparison between tears and meibum showed them to have similar lipid profiles, apart from phospholipids, which occurred roughly four orders of magnitude more abundantly in tears. This confirmed that meibum is not the major source of phospholipids in tears. No clear relationship between meibomian gland morphology and symptoms of discomfort was found, with the possible exception that meibomian gland coverage of the upper lid is reduced in those with more severe symptoms. For meibomian gland function, weak to moderate associations between ocular symptomatology and the position of Marx’s line and the frequency of eye rubbing were observed. Meibum quality and the relative proportion of (O-acyl)-omega-hydroxy fatty acid (OAHFA) in tears were found to potentially discriminate those with the most severe symptoms from the rest of the sample.