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Abstract
Ocular discomfort and dry eye symptoms are the main reasons for contact lens (CL) wear intolerance and discontinuation. In this context, dry eye and discomfort can be multifactorial, but with a growing clinical impression that physiological changes in the eyelid and meibomian glands (MGs) are involved. Yet, evidence is still inconclusive on the impact of CL wear on MGs and lid margin disease. Thus, this thesis aimed to observe the characteristics of the MGs, eyelids and tear film following varying durations of CL wear or previous CL wear. This thesis consists of three main studies that are clinical, histological and biochemical in nature.
In order to achieve this aim, a cross-sectional study was conducted involving a single observation of each member of a sample divided into five groups based on soft contact lens wearing experience. Three groups were existing CL wearers with different exposure durations (short, medium and long); one group had previously worn CLs and had now ceased; and a control group who had never worn CLs.
In the clinical study, a series of tests was applied to assess changes in the morphology and function of MGs, lid margin abnormalities, symptoms and related dry eye and ocular surface damage. Alterations to MG morphology and function, poorer tear film stability and lid margin characteristics were found to be associated with CL wear. Although these changes onset during the first two years of wear, prolonged CL exposure beyond this point does not appear to be associated with further modification. Cessation of wear for at least 6 months does not lead to resolution.
Following on from these observations a histological study was conducted to investigate the nature of cellular changes in the lid margin epithelium using the impression cytology technique. Histochemical analysis showed that CL wear altered lid margin epithelial cell morphology, cytoplasmic: nuclear ratio and goblet cell density but evidence for increased keratinisation was inconclusive. Next, biochemical studies examined two areas, first changes in the levels of inflammatory mediator MMP-9 in tears and second, the composition of meibum in the context of CL wear. The level of MMP-9 was relatively higher in early years of CL wear whereas meibum composition analysis did not reveal any specific changes with CL wear.