Alterations of ocular surface microbiome in glaucoma and its association with dry eyeOriginal paper
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease, four years before the first published case study.
Read MoreWhat was studied?
This study examined how the ocular surface microbiome changes in glaucoma, dry eye disease, and both conditions together. Researchers analyzed conjunctival swabs using 16S rRNA amplicon sequencing. They targeted the V1 to V3 region and clustered sequences into operational taxonomic units at 97 percent identity. Bacterial load was also quantified by 16S copy-number qPCR. The team compared alpha diversity, beta diversity, taxonomic composition, and predicted metabolic pathways across four groups. This is described as the first study to characterize the ocular microbiome in glaucoma patients who also have dry eye.
Who was studied?
Participants were 72 adults over 40 years old, recruited at Habib Bourguiba University Hospital in Sfax, Tunisia, between May 2021 and May 2023. Conjunctival swabs were taken from both eyes. The cohort included 31 healthy controls and 41 patients: 13 with glaucoma only, 15 with glaucoma plus dry eye, and 13 with dry eye only. Most glaucoma patients used intraocular-pressure-lowering drops preserved with benzalkonium chloride. Women were overrepresented in the dry eye groups. Of 144 eye samples, 139 yielded usable sequences.
What were the most important findings?
Sequencing revealed 28 phyla and 785 genera. Three phyla dominated across groups, at 67.47 percent, 17.14 percent, and 13.73 percent of total abundance. The most abundant phylum reached 82.21 percent in healthy controls but fell to 53.04 percent in the glaucoma-plus-dry-eye group. Beta diversity differed significantly between healthy controls and all three patient groups. The glaucoma-plus-dry-eye group showed higher alpha diversity than controls. Bacterial load by qPCR was significantly lower in glaucoma-only and dry-eye-only groups. Opportunistic, largely Gram-negative bacteria increased across all patient groups, most sharply in the combined group.
What are the greatest implications of this study?
The results indicate that ocular surface dysbiosis accompanies both glaucoma and dry eye disease, and that the two conditions together produce the most disturbed microbiome. Because the glaucoma-only group was also altered, the shifts in glaucoma are not simply due to dry eye. Predicted pathways pointed toward a pro-inflammatory environment, including lipopolysaccharide biosynthesis linked to Gram-negative bacteria. Preservatives such as benzalkonium chloride may drive these changes. The study was small, single-center, and lacked treatment-naive glaucoma patients, so preservative effects cannot be fully separated. Larger studies with species-level sequencing are needed.