Sruthi Srinivasan, PhD, BSOptom is a Research Assistant Professor at the Centre for Contact Lens Research, University of Waterloo.The prevalence of symptomatic dry eye in contact lens wearers is about 50-80%.1,2,3,4,5 Discontinuation from lens wear is primarily due to symptoms of discomfort and dryness.6,7,8,9 Increased tear evaporation and osmolarity,10,11 inflammation,12,13,14 and a non-wetting contact lens surface15,16 are some of the causes that have been proposed for the prevalence of dry eye in contact lens wearers.
Meibomian gland dysfunction: A major cause of dry eye
Recognition that meibomian gland dysfunction (MGD) is a major cause of evaporative dry eye has focused attention on the importance of examining the meibomian glands. However, MGD is often under-diagnosed and overlooked. There are mixed reviews in the literature on the association between MGD and contact lens wear.
Korb and colleagues reported that obstruction of the meibomian gland orifices is detected more frequently in contact lens intolerant patients than in asymptomatic contact lens wearers.17 Ong and others concluded that contact lens wearers develop MGD after six months.18 However, they found no significant difference between the meibomian gland lipids of contact lens wearers and non-wearers.19 Nichols and Sinnott20 found no significant structural changes in the meibomian glands of contact lens wearers reporting dry eye compared to contact lens wearers without dry eye symptoms. Studies conducted by a few other researchers failed to show significant differences when comparing the frequency of MGD between contact lens wearers and non-contact lens wearers.21,22 A recent study has shown that contact lens wear is associated with a decrease in the number of functional meibomian glands, which may also contribute to dry eye.23
The current definition of MGD
Earlier descriptions of MGD and its grouping were modified by the International Workshop on MGD, in 2011. The current definition of MGD proposed by the workshop report is as follows:
MGD is a chronic, diffuse abnormality of the meibomian glands, commonly characterized by terminal duct obstruction and/or qualitative/quantitative changes in the glandular secretion. This may result in alteration of the tear film, symptoms of eye irritation, clinically apparent inflammation, and ocular surface disease.24
The report of the Subcommittee on Epidemiology of MGDand Associated Risk Factors for MGD25 also concluded that the overall estimated frequency rate for MGD in contact lens wearers is not significantly different from the rate in non-contact lens wearers, suggesting that contact lens wear may not increase the risk for MGD. Nevertheless, limitations in size, design, and analysis conducted in studies related to MGD and contact lens wear prevent any sort of conclusive statements at this point.
Assessing MGD
Validated questionnaires (e.g. the Ocular Surface Disease Index) are needed for the assessment of symptoms and to monitor the progression of MGD26; however, the diagnosis of MGD solely with questionnaires is difficult because many of the symptoms presented by contact lens wearers with MGD echo the everyday complaints by contact lens wearers. Several non-contact, user- and patient-friendly instruments that allows for non-invasive, rapid evaluation of MG structure along with multiple other diagnostic functions are available. Evaluation of the eyelids, the tear film and the ocular surface using slit lamp biomicroscopy in conjunction with the use of specialized instruments will prove to be beneficial in determining the etiology of the underlying symptoms. Using instruments that apply a controlled amount of pressure on the lids to examine the meibomian gland secretions27 and the use of non-contact, patient-friendly meibographic (Figures 1a and b) techniques (upper and lower lid meibography),28,29,30 confocal microscopy in the assessment of the acinar density,31,32 and analysis of the lipid layer using interferometry are useful in determining the status and severity of MGD.
Figure 1a: Meibography of the upper lid of a CL wearer
Figure 1b: Meibography of the lower lid of a CL wearer
The majority of clinical trials on MGD conducted in the past have considered contact lens wear an exclusion criterion. Hence, the impact of contact lens wear on meibomian gland acinar changes, the quality of the meibum produced by the meibomian gland and its impact on lipid layer thickness and quality need further exploration. Laboratory analysis of meibum in symptomatic and asymptomatic contact lens wearers with MGD is also required. If MGD is prevalent in contact lens wear and this association can be linked to dryness and discomfort, it may be possible to reduce the number of dropouts.
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