Review articleNon-invasive objective and contemporary methods for measuring ocular surface inflammation in soft contact lens wearers – A review
Introduction
The use of contact lenses is one of the primary risk factors associated with corneal and ocular surface inflammatory events [1], [2], [3], [4]. It has been reported that soft contact lens related corneal inflammatory and infiltrative events occur in 7–44% of wearers per year and are associated with significant morbidity and economic cost (>$175 million US dollars in 2010, USA) [1], [5], [6], [7]. Contact lens induced adverse events can be inflammatory and/or infectious in nature [2], [8]. Contact lens wear can induce hypoxic or mechanical stress on the ocular surface and may also act as a vehicle for microbial inoculation, leading to pathogenic events ranging from subtle epithelial injury and infiltration by pathogens, antigens and white blood cells to the most severe microbial keratitis (MK)[9].
It has been hypothesized that a contact lens on the eye induces an ocular surface inflammatory process. Efron has comprehensively shown how contact lens wear can lead to the five cardinal signs of inflammation (mild and severe) that are clinically seen on the ocular surface namely- rubor (redness), calor (heat), tumor (swelling), loss of function (Functio laesa) and dolor (pain), which is encompassed as discomfort [10], and this is consistent with the Merriam- Webster dictionary definition of inflammation. Even though the forms of inflammations are mild in successful contact lens wearers, cardinal signs, such as hyperaemia [11], increased ocular temperature when wearing contact lens [12], [13], symptoms [14], and corneal oedema in subjects who wear low oxygen transmissibility contact lenses [15], can be more readily observed than in non-contact lens wearers. These milder forms of inflammation can be managed by altering the contact lens material, fitting, decreasing wearing time and instillation of artificial tears [13], [15], [16], [17]. However, in severe cases, the contact lens induced inflammation can lead to adverse events that warrant discontinuation of lens wear [18].
A large proportion of soft contact lens wearers report ocular dryness and discomfort [19], [20]. It has been stated that this, so-called, ectopic corneal pain could be due to subclinical inflammation with the presence of normal tear secretion and corneal sensitivity [21], [22]. Contact lens wear has been shown to induce higher ocular temperature and conjunctival hyperemia, which supports the notion that soft contact lens wear induces ocular surface inflammation, along with other compromised ocular surface parameters, such as lower tear stability and higher ocular surface staining [13], [23], [24], [25].
This manuscript aimed to review the findings of these non-invasive contemporary techniques for detecting inflammatory responses at the cellular and molecular levels, including a) Ocular inflammatory response related to contact lens wear in humans; b) Recent objective methods used to evaluate the inflammatory responses on the ocular surface; and c) Potential factors that may be related to the risk of ocular inflammatory events in contact lens wearers.
Section snippets
Ocular surface inflammation in contact lens wear
The proposed mechanism driving this contact lens related inflammatory response can be described in two main steps: First, the ocular surface releases pro-inflammatory molecules and proteins [2], [26] in response to the presence of a contact lens. These proteins then modulate the ocular surface (i.e, migration of antigen presenting cells and changes in the morphology of conjunctival cells) and these changes further drive the inflammatory cascade, in a vicious cycle (Fig. 1) [27]. These
Evaluation of ocular surface inflammation at the cellular and molecular level
In this section, the methodology of sample collections and analyses of tear inflammatory mediators, conjunctival cell morphology, including goblet cell density and epithelial squamous metaplasia, and antigen presenting cells on the ocular surface and the effects of contact lens wear are discussed.
Factors affecting ocular surface inflammation
Contact lens wear related factors, such as duration of wear, lens power, replacement schedule and lens materials [1], [178]; and behaviors and non-modifiable patient factors, such as age and sex, must be taken into consideration when investigating contact lens related ocular surface inflammation. For example, the peak prevalence for contact lens induced corneal inflammatory events occurs in 15–44 years old [178], [179], [180], [181]. However, the effect of age and innate immune system in
Conclusion
Recent improvements in technology have significantly increased the ability to quantitatively and objectively assess the inflammatory status of the human ocular surface in vivo. This manuscript provided a review of contemporary techniques to measure the inflammatory responses on the ocular surface during contact lens wear, and highlighted the potential limitations of techniques and challenges comparing results across studies, suggesting that standardizing test methods and interpretations are
Conflict of interest
The authors have no proprietary or commercial interests in any concept or product discussed in this article.
This review did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors.
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2019, Experimental Eye ResearchCitation Excerpt :A certain degree of MMP-driven ECM remodelling may be a necessary step for cornea healing, but an imbalance in this tightly regulated process may, in the long term, result in the progressive weakening of the cornea (Fig. 2). Eye rubbing and contact lens wearing have a clear link with ocular surface inflammation (Chao et al., 2017; Greiner et al., 1985). Although KC is generally considered a non-inflammatory eye condition (Krachmer et al., 1984), this is still under debate (Galvis et al., 2015; Ionescu et al., 2016; McMonnies, 2015).