Abstract
Purpose :
Keratoconus(KC) is characterised by irregular astigmatism due to focal thinning and protrusion of the cornea. Inflammatory factors in the cornea and tear film have been shown to correlate with disease severity. The resident tissue microbiomes can influence the immune status in other organs, but has not been described in human ocular disease. We analysed the resident ocular surface microbiome of KC patients in relation to their tear molecular profile.
Methods :
Approval of Institutional Ethics Committee and written informed consent from the subjects were obtained prior to sample collection. Swabs from the lower corneal fornix was obtained from 15 healthy controls and 34 KC subjects. All subjects underwent topography, visual acuity and ocular surface examination. Tear samples were collected using Schirmer’s strips. Microbiome analysis was performed by V3-V4 amplicon sequencing followed by bioinformatics analysis of long read non-chimera sequences to obtain operational taxonomic units corresponding to phyla, class order, family and genus. 39 molecular factors were measured from Schirmer’s strip tear extracts by multiplex ELISA on Flow Cytometer.
Results :
We identified 21 phyla, 53 classes, 103 orders, 213 families and 515 genus in our cohort. Four phyla, Actinobacteria, Proteobacteria, Firmicutes and Bacteroidetes, were dominant across the groups. Actinobacteria reduced across KC grades but Alphaproteobacteria increased across KC grades compared to controls. Propionibacterium was the predominant genus, followed by Corynebacterium and Staphylococcus. Lactobacilli, Streptococcus, Rothia and Brevibacterium were reduced across KC grades compared to controls. Dienococcus, Brevundimonas, Phycicoccus and Bacillus increased across KC grades. IL8, CD121 and MPO levels significantly correlated with Actinobacteria (p<0.05). Proteobacteria positively correlated with IL17A and IL12 (p<0.05). Bacteroidetes correlated with Perforin levels (p<0.05).
Conclusions :
The data uncovers a unique microbiome signature of KC that also correlated with disease severity suggesting a causal relationship with the pathology. The association of certain phyla and genera with tear molecular factors indicate that there exist underlying interactions of the immune mediators with resident microbiome on the ocular surface which may be pathologic in KC.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.