Tear collection presents alternative to conjunctival swabs

A study by Dr Arunasri et al from the Brien Holden Eye Research Centre, and The Cornea Institute, both at L V Prasad Eye Institute, compares the tear microbiome of healthy adults to the ocular surface microbiome obtained using conjunctival swabs. The study opens up the possibility of using tear samples instead of conjunctival swabs, especially for patients in pain due to injury or infection. 

The ocular microbiome—the diversity of microbes that live on the ocular surface—has a role to play in understanding the healthy and diseased states of the eye. The standard tool to sample microbiota from the ocular surface is a conjunctival swab, where a swab is rubbed on the conjunctiva to collect the sample. This is a direct method and greatly reduces the risk of contamination from other sources. However, the procedure for collecting conjunctival swabs can be painful for patients with an injury or infection. There is a need for a less-invasive method of sample collection from this ocular region.

A new paper by Dr Arunasri Kotakonda and her colleagues from L V Prasad Eye Institute presents an alternative, a less invasive sample collection method to establish the ocular microbiome: sampling tears. The paper addresses three potential issues: identifying the microbiome that constitutes a healthy eye; noting any variation based on age and gender; and measuring differences between tear samples and conjunctival swabs. The study looked at 15 healthy participants (nine male and six female), aged 20-52 years. 

The paper reports several interesting findings. After identifying the different bacterial genera that constitute the tear microbiome, the authors identify their abundance and distribution. While previous studies had found differences in the ocular microbiota between children and older adults, the present study finds homogeneity among adults of 20-52 years age. The group also notes no significant differences in the microbial communities of the left and right eye, nor do they find any variation based on gender or age within this cohort. These findings add to the small but growing literature documenting the microbiome of a healthy eye. Such a baseline will be important to understand the impact of dysbiosis in a diseased eye. 

For the primary purpose of comparing the similarity of a tear sample with that of a conjunctival swab, the group used conjunctival swab data from their previous study. Despite significant differences in abundance, the group found that nearly all the genera obtained through swabs correlated with that found in tears. Pseudomonas, Corynebacterium, and Staphylococcus that are common commensals of the ocular surface were similarly abundant in both samples. Though they do not explain why, the group found that Bacillus and Lactobacillus were more abundant in tears.  

This paper establishes the broad similarities between the microbiota identified using conjunctival swabs and tears. This sets the stage to explore less-invasive techniques like tear collection to identify the bacterial microbiome of the ocular surface. 

'This study helped in identifying a less invasive sampling method to study the ocular microbiome,' says Dr Arunasri Kotakonda, the corresponding author for the paper. 'This research will benefit all ocular microbiome researchers in collecting ocular samples without compromising on quantity and quality. It will help in understanding the dysbiosis or the imbalance of the microbiome in healthy compared to various ocular diseases.' 

Dr Shivaji Sisinthy, Distinguished Scientist, Prof Brien Holden Eye Research Centre, and an author on this paper, says, 'the findings that the tear microbiome is a gross reflection of the microbes present on the conjunctiva and additionally that the tear microbiome is not influenced by confounding factors like age, gender and the eye it is collected from makes it a convenient, non-invasive method for sampling compared to the traditional swab method.'

Pal S, Vani G, Shivaji S, Donthineni PR, Basu S, Arunasri K. Characterising the tear bacterial microbiome in young adults. Exp Eye Res. 2022 Jun;219:109080. doi: 10.1016/j.exer.2022.109080. Epub 2022 Apr 17. PMID: 35443208. 

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