Microbiome Of Pterygium

Pterygium is a disorder of the ocular surface characterized by abnormal conjunctival growth. Although ultraviolet light exposure is recognized as the primary risk factor, the precise pathogenesis of pterygium remains incompletely understood. To gain deeper insight into the mechanisms underlying its development, we analyzed pterygium tissue and compared it with healthy conjunctival controls. Given that the conjunctiva is continuously exposed to environmental factors and is colonized by diverse microorganisms, it is plausible that certain microbial populations may contribute to pterygium formation. Accordingly, this study aimed to identify and characterize microbiota constituents potentially involved in the development of pterygium.

We enrolled patients undergoing primary pterygium surgery at the Department of Ophthalmology, University Hospital of Split, between September 2017 and January 2019. Control samples were collected from patients undergoing cataract surgery between September 2021 and January 2022.

Excised pterygium tissue overlying the cornea and control samples of healthy conjunctiva adjacent to the corneoscleral junction were collected at the start of surgery to minimize contamination and tissue manipulation. Microbiota composition was analyzed using metagenomic sequencing of pterygium specimens to identify microorganisms potentially associated with the condition. In addition, fluorescent in situ hybridization was performed to visualize Malassezia species in the collected samples.

Metagenomic sequencing identified an increased prevalence of the fungus Malassezia restricta in five pterygium samples, a finding further confirmed by in situ hybridization. The CHIT1 gene, involved in antifungal defense mechanisms, showed the highest expression levels in these five pterygium tissues compared with healthy conjunctival controls, supporting a potential role for Malassezia restricta in pterygium pathogenesis. Gene expression profiling further revealed an IL-33 and IL-4–associated transcriptional signature, accompanied by an elevated presence of M2 macrophages, underscoring their contribution to fibrosis, a hallmark characteristic of pterygium.

The identification of Malassezia restricta in pterygium specimens, together with the associated molecular alterations, offers new insights into the ocular microbiome and suggests a potential role for Malassezia in the pathogenesis of pterygium.