Elsevier

The Ocular Surface

Volume 16, Issue 2, April 2018, Pages 198-205
The Ocular Surface

Review Article
Effects of environment pollution on the ocular surface

https://doi.org/10.1016/j.jtos.2018.03.001Get rights and content

Abstract

The twenty-first century is fraught with dangers like climate change and pollution, which impacts human health and mortality. As levels of pollution increase, respiratory illnesses and cardiovascular ailments become more prevalent. Less understood are the eye-related complaints, which are commonly associated with increasing pollution. Affected people may complain of irritation, redness, foreign body sensation, tearing, and blurring of vision. Sources of pollution are varied, ranging from gases (such as ozone and NO2) and particulate matter produced from traffic, to some other hazards associated with indoor environments. Mechanisms causing ocular surface disease involve toxicity, oxidative stress, and inflammation. Homeostatic mechanisms of the ocular surface may adapt to certain chronic changes in the environment, so affected people may not always be symptomatic. However there are many challenges associated with assessing effects of air pollution on eyes, as pollution is large scale and difficult to control. Persons with chronic allergic or atopic tendencies may have a pre-existing state of heightened mucosal immune response, hence they may have less tolerance for further environmental antigenic stimulation. It is beneficial to identify vulnerable people whose quality of life will be significantly impaired by environmental changes and provide counter measures in the form of protection or treatment. Better technologies in monitoring of pollutants and assessment of the eye will facilitate progress in this field.

Introduction

Air pollution is a serious health issue that impacts quality of life, as long term exposure is associated with respiratory and cardiovascular problems [[1], [2], [3]], as well as increased hospital admissions and healthcare spending [4,5]. These phenomena have been observed in the west as well as in Asia [6], and with urbanization, such problems are expected to worsen with time [7]. In severe cases, pollution can even increase mortality [[10], [8], [9]], and adversely affect intrauterine growth [11]. By improving environmental conditions, it has been shown that health indicators can respond favorably [3].

According to the World Health Organization, air pollution consists of different particulate including particulate matter (PM), ozone, carbon monoxide (CO), nitrogen dioxide (NO2) and sulfur dioxide (SO2). The number after PM refers to the aerodynamic diameter of the particles; i.e. PM10 refers to particles <10 μm, and PM2.5 refers to particles less than 2.5 μm PM10 is generated from construction and road dust, whilst smaller particles (PM2.5) is derived from combustion sources such as wood and biomass fuels. Regardless of the type of pollutant, pollution is an widespread issue as it can affect occupations both outdoors [12] and indoors [13].

Air pollution can affect the eye, causing complaints of eye redness, irritation, watering, foreign body sensation, and blurring of vision; however the link to the environment is sometimes overlooked by eye professionals [14]. Since the ocular surface can be easily examined, it can serve as an indicator of the impact of pollution on health [15,16]. Despite the importance of the effects of pollution on the eye, contemporary research in this area has not been reviewed recently in regards to associations of the types of pollution with clinical signs and symptoms [17,18].

We aim to conduct a literature review of publications in the last 10 years. The search strategy was to retrieve relevant English articles published in Entrez Pubmed from November 2007 to January 2017, using the keywords “ocular surface”, “pollution”, “dry eye”, “conjunctiva” and “cornea”. Review articles published previous did not have the same scope (individual review described only symptoms or limited to clinical signs) and were not included in this current report [19,20].

Section snippets

Environments affecting the eye

Involvement of pollution on the ocular surface has been summarised in 5 population surveys (Table 1). These studies involved whole cities or towns and it is difficult to know which ecosystem within the geographical area is relatively more affected by pollution. These 5 studies were selected as they represent environments where there are chronic exposures to typical pollutants in their respective regions with primary focus on ophthalmic consequences. Therefore, we will next examine studies which

Methods of assessing ocular surface

There are a variety of methods for assessing effects of environment on the ocular surface. The biggest complaint is dry eyes are the symptoms are measured with different scoring questionnaires available, such as the Ocular Surface Disease Index (OSDI), Standard Patient Evaluation of Eye Dryness (SPEED) and Symptom Assessment iN Dry Eye (SANDE). These questionnaires assess the reported frequency of eye irritation, dryness, tearing or blurring of vision. These standardized questionnaires make it

Mechanisms

Some mechanisms causing ocular surface problems are toxicity, oxidative stress, and inflammation from gases and traces of particles in the atmosphere (Fig. 1).

Human studies

Limitations exist in human studies, as air pollution is very difficult to control and standardize. Many different living and environmental factors exist in a polluted city, and some may be unrelated to the pollution. For example, people may be living in a more stressful environment or have less time for physical exercise and proper diet. Potential confounding factors also include seasonal effects like atmospheric pollen exposure and genetic differences. In addition, large population studies

Conclusion

Air pollution has a significant impact on ocular surface, and in people predisposed to immune triggers, it is likely to incur marked morbidity and reduce quality-of-life. Although the loss of immune tolerance and involvement of pro-inflammatory cytokines are suspected to play a role, the detailed mechanisms through which air pollutants interfere with tear film, cornea and conjunctiva still remain unclear. At the present moment, it is unclear if the composition or the immunological regulatory

Conflicts of interest

Nil.

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