How the ocular microbiome may shape outcomes in keratoplasty

Corneal transplant candidates exhibit a distinct ocular surface microbial profile characterized by increased diversity and enrichment of opportunistic bacteria compared with healthy controls, according to findings published in Cornea.¹

Diversity and community composition

In this single-centre case–control study, Astolfi et al, of the Alma Mater Studiorum University of Bologna and IRCCS Azienda Ospedaliero-Universitaria di Bologna, Italy, collected conjunctival swabs from 54 adults scheduled for lamellar or penetrating keratoplasty and 16 healthy controls immediately before surgery. Microbial DNA from conjunctival samples was characterized using 16S rRNA gene sequencing of the V3–V4 hypervariable regions. Within-sample diversity was quantified by the Shannon index, while compositional differences between groups were assessed using Bray–Curtis dissimilarity and PERMANOVA.

Pretransplant patients showed significantly higher alpha diversity than healthy controls (P = .04), and beta diversity analysis confirmed distinct microbial community structures between groups (P = .002), accounting for 2.5% of total compositional variation. Taxonomic analysis identified enrichment of Enterobacteriaceae, Pseudomonas, and Escherichia–Shigella in the patient group, while Bacteroidota and Bacteroidia predominated in healthy subjects.¹ The authors noted that on the ocular surface, elevated microbial diversity may reflect dysbiosis, potentially driven by disrupted epithelial integrity, altered tear film composition, or changes in local immune responses.

Role of decompensation and surgical history

No significant differences in alpha or beta diversity were observed between decompensated and nondecompensated patients (P = .73 and P = .72, respectively), suggesting that the degree of endothelial decompensation does not substantially alter microbial community structure within the pretransplant population. However, when decompensated patients were stratified by surgical history, those with a history of penetrating keratoplasty had markedly higher microbial diversity than patients whose only prior procedure was phacoemulsification with intraocular lens implantation (P = .03), a finding the authors attributed to long-term changes in ocular surface physiology following full-thickness corneal transplantation.¹

Comparison between decompensated and nondecompensated subgroups revealed that nondecompensated patients had higher relative abundances of Firmicutes (28.2% vs 15.9%, P = .001) and Bacilli (23.4% vs 13.7%, P = .006), while Gammaproteobacteria were enriched in decompensated cases (18.7% vs 32.4%, P = .004).¹ The authors noted that the higher abundance of Bacilli in nondecompensated patients may point toward microbe-based strategies for corneal disorder prevention, given the probiotic properties of some species within this class.

Implications for preoperative assessment

The authors acknowledged several limitations, including the exploratory, single-centre design; small sample size; cross-sectional methodology precluding causal inference; and 16S rRNA sequencing resolution limited to the genus level. They called for confirmation in larger prospective cohorts.²

The authors concluded that the ocular surface microbiome is altered in patients awaiting corneal transplantation in patterns associated with chronic corneal disease and surgical history, rather than with the degree of endothelial decompensation. They proposed that preoperative microbiome profiling could inform perioperative management and risk stratification for postoperative complications, consistent with evidence linking microbiome dysbiosis to increased mortality following solid organ transplantation.^1-3

The authors reported no conflicts of interest or funding to disclose.

References

1. Astolfi A, Potenza M, Ciavarella C, et al. Distinct ocular surface microbial profiles in corneal transplant candidates. Cornea. Published online June 12, 2026. doi:10.1097/ICO.0000000000004088

2. Potenza M, Moramarco A, Astolfi A, Ciavarella C, Fontana L, Versura P. Ocular surface microbiota and corneal transplant outcome: is there a link? Biomedicines. 2025;13(4):972. doi:10.3390/biomedicines13040972

3. Swarte JC, Li Y, Hu S, et al. Gut microbiome dysbiosis is associated with increased mortality after solid organ transplantation. Sci Transl Med. 2022;14(660):eabn7566. doi:10.1126/scitranslmed.abn7566