Disturbing the balance: effect of contact lens use on the ocular proteome and microbiome

Abstract

Contact lens wear is a popular, convenient and effective method for vision correction. In recent years, contact lens practice has expanded to include new paradigms, including orthokeratology; however, their use is not entirely without risk, as the incidence of infection has consistently been reported to be higher in contact lens wearers. The explanations for this increased susceptibility have largely focused on physical damage, especially to the cornea, due to a combination of hypoxia, mechanical trauma, deposits and solution cytotoxicity, as well as poor compliance with care routines leading to introduction of pathogens into the ocular environment. However, in recent years, with the increasing availability and reduced cost of molecular techniques, the ocular environment has received greater attention with in‐depth studies of proteins and other components. Numerous proteins were found to be present in the tears and their functions and interactions indicate that the tears are far more complex than formerly presumed. In addition, the concept of a sterile or limited microbial population on the ocular surface has been challenged by analysis of the microbiome. Ocular microbiome was not considered as one of the key sites for the Human Microbiome Project, as it was thought to be limited compared to other body sites. This was proven to be fallacious, as a wide variety of micro‐organisms were identified in the analyses of human tears. Thus, the ocular environment is now recognised to be more complicated and interference with this ecological balance may lead to adverse effects. The use of contact lenses clearly changes the situation at the ocular surface, which may result in consequences which disturb the balance in the healthy eye.

Proteomics Unravels the Regulatory Mechanisms in Human Tears Following Acute Renouncement of Contact Lens Use: A Comparison between Hard and Soft Lenses

“…Ultimately, an inability to tolerate DNA damage will lead to cell death 18 . The use of hard contact lenses frequently confers mechanical damage on the cornea because they are designed to move on the eye when the wearer blinks, which could pose a significant risk of epithelial cell death and consequently lead to alterations in tear constituents 5 , 22 , 23 . Interaction of tear film with the epithelia has been shown to be pivotal in maintaining homeostasis of the ocular surface and cells at the anterior segment of the eye contribute to the tear film composition to exert protection from various insults to the eye 24 .…”

“…Soft CLs are in contact with both conjunctiva and cornea and thus, may provoke abnormal dryness of these tissues by destabilizing the structure of the tear film, particularly within the protective lipid layer which functions to impede evaporation 31 – 33 . An elevation of tear osmolality as an adaptive mechanism to the use of CLs has been associated with the development of dry eye 5 . Furthermore, the augmentation of normal levels of existing regulatory molecules is often a host defence mechanism in response to antigenic stimuli and foreign objects such as CLs 12 .…”

“…The activation and influx of additional new components or augmentation of existing components in tears are also attributable to the frictional interaction and movement of the eyelid with the CL over the ocular surface 12 . Hard CL wearers are more exposed to fricto-mechanical stimulation than their soft counterparts owing to the material stiffness and movement of the lens edges during blinking, which could have resulted in minor injury to the cornea, however modest though that may be 5 , 11 , 23 . Although a large majority of VTN originates from conjunctiva, other main endogenous reservoirs of VTN include tear film and the basement membrane of corneal epithelium 41 , 42 .…”

“…Currently, there are approximately 14 million CL wearers worldwide and this number is growing steadily every year 3 , 4 . Albeit fascinating technological advancements in improving the quality and biocompatibility of the lenses over the years, CLs are still foreign objects on the ocular surface, which alter tear homeostasis by disrupting tear film stability and changing the levels of tear molecular constituents 5 , 6 . It is, therefore, not surprising that CL-induced inflammation is one of the major causes of morbidity in the United States of America 7 .…”

The Role of Hypoxia in Corneal Extracellular Matrix Deposition and Cell Motility

“…Pathologies such as diabetes, herpes simplex virus infection, dry eye syndrome, and limbal stem cell deficiency can cause a transition to a hypoxic state, where oxygen levels are at or below 8% for various time periods (Boost et al ., ; Kanda et al ., ; Kim et al ., ; Sanyal et al ., ). Under these conditions, vascularization of the cornea may occur.…”