The interaction between a contact lens and the ocular surface is key to achieving success with lens wear. Over recent years, we have become far more cognizant of this intimate relationship. Abnormalities in the ocular surface that are often associated with dry eye disease can create great challenges to contact lens wear. Additionally, contact lenses can significantly exacerbate signs and symptoms of ocular surface and dry eye disease. Finally, certain contact lenses may be therapeutically used to address ocular surface diseases for specific cases.
We will explore what the research is telling us about this critically important relationship between contact lenses and ocular surface disease. Evidence-based clinical practice will help eyecare professionals to both manage ocular surface disease for their contact lens patients and to know when to incorporate specific contact lens designs to address appropriate cases of dry eye and ocular surface disease.
Meibomian Gland Dysfunction
Although there may be no significant difference in the incidence of meibomian gland dysfunction (MGD) between contact lens wearers and non-lens wearers, contact lenses can impact the structural and functional integrity of the meibomian glands (Alghamdi et al, 2016; Arita et al, 2009). Contact lens wear, and specifically duration of wear, has been associated with a decrease in the number of functional meibomian glands (Arita et al, 2009). It is unclear whether the physical wear of contact lenses alters meibum composition and/or whether there is a relationship between meibum composition and contact lens comfort (Arita et al, 2009).
A cross-sectional study by Machalińska et al (2015) that compared meibomian gland characteristics in soft contact lens wearers and non-lens wearers reported that contact lens use was associated with abnormal meibum composition and more extensive meibomian gland stasis. Meibum quality scores highly decreased as contact lens wear duration increased. These findings highlight the importance of routinely evaluating meibomian gland integrity and expressibility to ensure early intervention for any underlying or advanced MGD (Machalińska et al, 2015).
Tear film lipid deposits can occur on the surface of all contact lenses, but they can especially occur with silicone hydrogel materials (Hagedorn et al, 2015). The lipids from individuals who have MGD tend to deposit irregularly on the surface of a contact lens, whereas lipids from patients who have healthy glands spread more uniformly on the lens surface (Hagedorn et al, 2015). Further research is needed to determine the extent of interindividual variability in meibum composition, whether this relates to contact lens comfort, and how contact lens wear potentially alters meibum composition (Hagedorn et al, 2015).
There are conflicting reports relating to the possible association between contact lens wear and meibomian gland dropout (Efron et al, 2013; Downie and Craig, 2017). Changes to meibomian gland structure have been reported to be associated with contact lens wear and are evident most during the first couple of years of contact lens wear, after which the gland structure remains relatively constant over longer wear periods (Alghamdi et al, 2016; Downie and Craig, 2017). Performing meibography scans of the superior and inferior lids is extremely relevant in assessing baseline and progressive meibomian gland structural changes and intervening to aid in reduction of meibomian gland dropout (Downie and Craig, 2017).
Human tear film has a vastly complex structure consisting of multiple layers, including the lipid layer on the surface and a thicker, aqueous-mucin phase, which increases in mucin concentration toward the corneal epithelium (Downie and Craig, 2017). The health of the tear film and of the ocular surface affects the likelihood of achieving successful contact lens wear. Contact lens discomfort and dryness are the most frequent reasons why contact lens wearers drop out of contact lenses (Young, 2004). Comprehensive clinical assessment of tear film integrity and ocular surface health is therefore essential prior to fitting contact lenses to enable the ocular surface environment to be optimized for successful lens wear.
These criteria should also be evaluated over the course of contact lens wear to ensure that optimal lens-wearing conditions are maintained. Additionally, practitioners should address subjective complaints and objective clinical findings when necessary (Downie and Craig, 2017).
When fitting and evaluating contact lenses for our patients, we must emphasize the importance of early and accurate diagnosis of dry eye disease for successful long-term GP and soft contact lens wear.
The application of a contact lens to the eye can alter the integrity of both the tear film and the ocular surface microenvironment. In essence, a contact lens artificially compartmentalizes the tear film into pre- and post-lens layers in situ, affecting its biochemical and biophysical characteristics and reducing tear stability (Downie and Craig, 2017; Craig et al, 2013).
At approximately two microns thick, the pre-lens tear film is thinner than the pre-corneal tear film is by approximately one micron, which likely exposes the tear fluid to more rapid destabilization (Downie and Craig, 2017; Chen et al, 2010). Therefore, subjective awareness of ocular dryness and symptoms of discomfort are common with contact lens wear; contact lens wearers tend to experience these symptoms more frequently compared to non-lens wearers. Asymptomatic contact lens wearers show a higher basal tear flow rate than symptomatic wearers do, helping to counteract the loss of tear fluid from the higher tear evaporation rate witnessed in contact lens wear (Downie and Craig, 2017).
Evaluation of the conjunctiva should include an assessment for the presence of lid-parallel conjunctival folds (LIPCOFs), which are an indication of ocular surface dryness. Additionally, because LIPCOFs are located adjacent to the lid margin, they can impede the formation of a normal tear reservoir (Downie and Craig, 2017).
Most contact lens types (excluding corneal GPs) completely cover the cornea and extend onto the bulbar conjunctiva, moving on the conjunctiva with each blink. This interaction with sustained contact lens wear results in conjunctival changes at the clinical and cellular levels. It is also associated with contact lens discomfort. The bulbar conjunctiva is important in the maintenance of tear film integrity and mucin production (made by goblet cells along the conjunctival epithelium) (Markoulli and Kolanu, 2017). It is this exact mucus that comprises the innermost layer of the tear film.
Anything that puts stress on the goblet cells may interfere with mucin production, thus disrupting the tear film and resulting in symptomatic dry eye (Markoulli and Kolanu, 2017). At the cellular level, contact lens wear has been shown to cause conjunctival metaplasia, which is caused by mechanical friction. Goblet cell density decreases following a three- and six-month period of contact lens wear; this is typically worse in symptomatic wearers, but it is reversible once contact lens use is discontinued (Markoulli and Kolanu, 2017).
It is interesting to note that the practice of orthokeratology lens wear has been shown to improve comfort and to increase goblet cell density one month after the termination of silicone hydrogel lens wear (Markoulli and Kolanu, 2017). This may suggest that orthokeratology could be considered an alternative (for the right candidates) for those patients who are intolerant of daytime-use contact lenses (Markoulli and Kolanu, 2017).
At the clinical level, the use of contact lenses interferes with the thin tear layer so that direct contact with the ocular surface (i.e., the conjunctiva) is inevitable. This is evidenced by conjunctival staining, conjunctival indentation, conjunctival epithelial flaps, and conjunctivochalasis (Markoulli and Kolanu, 2017).
The stress of contact lens wear on the conjunctiva and the presence of contact lens discomfort suggest that close monitoring of remarkable conjunctival findings at follow-up visits may assist in detecting those patients who are more likely to develop contact lens awareness/discomfort. In addition, managing the friction responsible for these findings may prevent possible contact lens wear dropout (Markoulli and Kolanu, 2017).
Practitioners cannot attempt to successfully manage patients with contact lenses without paying careful attention to the status of the ocular surface and the tear film. Treating pre-existing ocular surface anomalies and addressing problems that are exacerbated by contact lens wear will dramatically increase the likelihood of optimal lens wear outcomes. CLS
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