Introduction
Plastics are synthetic materials created from organic polymers that are commonplace in daily life and crucial in medicine. Nevertheless, Recent developments have highlighted the ubiquitous nature of microplastics produced by decomposing current plastic goods. Microplastics may cause oxidative stress, microbial dysbiosis, and inflammation in people, according to a growing body of research.
The terms “microplastics" and "nanoplastics" refer to the tiny particles produced during the breakdown of all plastics. "microplastic" was originally used to refer to tiny plastic fragments found in marine sediments in 2004. These come in primary and secondary microplastic forms. Small-produced microplastics, including resin pellets and microbeads, are considered primary microplastics. When bigger plastic particles like plastic bottles or bags break down, secondary microplastics are created.
What Are the Sources and Routes of Exposure to Microplastics?
One potential environmental source is exposure to fluids or the environment with microplastic contamination. Polypropylene, polyethylene, polystyrene, and polyethylene terephthalate are the most commonly discovered microplastics in the environment. Estimates of these particles' half-lives vary depending on their polymer makeup, the surrounding environment, and their thickness.
For example, low-density polyethylene has a half-life of 3.4 years in the ocean and 4.6 years when buried. The half-life is significantly decreased in the presence of environmental conditions like heat and UV irradiation. There are airborne microplastics in vehicle exhaust gas. Other sources include landfills, incinerators, industrial pollutants, fertilizers used in agriculture, and synthetic fabrics.
Microplastics have also been found in the surgical context, and it is considered that their prevalence in the hospital environment results from the widespread usage of plastics. It is probable that eye drops contain microplastics, given the numerous reports of microplastics coming from commonplace things like bottled water and ubiquitous plastic packaging. This is concerning because those who have chronic conditions like dry eye disease and glaucoma, which call for repeated and extended eye drop instillation, may unintentionally expose the ocular surface to microplastics included in topical ophthalmic formulations. This exposure is significant yet rarely recognized.
What Is the Impact of Microplastics on the Ocular Surface?
According to in vitro studies, polystyrene microplastic particles could be taken up by human corneal and conjunctival epithelial cell lines, with the microplastics settling around the cell nuclei. Reductions in tear volume, tear film break-up time, and loss of corneal epithelial microvilli and desmosomes occur when the murine ocular surface is exposed to particulate matter 2.5 (PM2.5) environmental pollutants, which can contain microplastics. On the ocular surface, elevated TNF- and NF-B p65 levels suggested ocular surface disorders resembling human dry eye disease.
What Are the Proposed Mechanisms of Tissue and Cell Damage?
It is well known that inflammation plays a significant pathogenic and aggravating role in the development of dry eye disease. Inflammation and dry eye disease can be brought on by oxidative stress. People with dry eyes have increased oxidative stress indicators such as malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), which are late lipid peroxidation markers. The severity of the condition was significantly linked to MDA levels. In particular, inflammatory cell infiltration across the ocular surface was linked to the formation of reactive oxygen species (ROS).
Microplastic exposure in the intestine raised the expression of glutathione S-transferase 4 and lipid peroxidation while decreasing catalase and glutathione reductase, indicating that oxidative damage is a major mechanism causing epithelial damage brought on by microplastics.
Changes in the ocular surface microbiota have been linked to ocular surface disorders. For instance, patients with dry eye disease associated with meibomian gland dysfunction have higher abundances of Firmicutes and Proteobacteria, and lower levels of Actinobacteria. In contrast, patients with aqueous tear-deficient dry eyes have an increased abundance of Brevibacterium and a decreased amount of Pseudomonas. The ocular surface microbiome may significantly influence the etiology and progression of ocular surface disorders because it is likely to maintain homeostasis and modify ocular surface immune function.
Conclusion
Plastics are widely available and generally cheap to manufacture. Plastics continue to be used in various industries, including healthcare, for various purposes. With the extensive use of topical ophthalmic formulations, surgical tools, contact lenses, and syringes for intraocular therapeutic drug administration, the field of eye care is not an exception. A growing body of research suggests that microplastics and nanoplastics may negatively influence human health by altering the microbiota or immunology of the ocular surface or by inducing oxidative stress or cell death.
