Central corneal thickness and the risk of primary open-angle glaucoma: a Mendelian randomisation mediation analysis

Background The association of central corneal thickness (CCT) with primary open-angle glaucoma (POAG) remains uncertain. Although several observational studies assessing this relationship have reported an inverse association between CCT and POAG, this could be the result of collider bias. In this study, we leveraged human genetic data to assess through Mendelian randomisation (MR) the effect of CCT on POAG risk and whether this effect is mediated by intraocular pressure (IOP) changes. Methods We used 24 single-nucleotide polymorphisms (SNPs) associated with CCT (p value<5x10(-8)) from a genome-wide association study (GWAS) (N=17 803) provided by the International Glaucoma Genetics Consortium and 53 SNPs associated with IOP (p value<5x10(-8)) from a GWAS of the UK Biobank (UKBB) (N=97 653). We related these instruments to POAG using a GWAS meta-analysis of 8283 POAG cases and 753 827 controls from UKBB and FinnGen. Results MR analysis suggested a positive association between CCT and POAG (OR of POAG per 50 mu m increase in CCT: 1.38; 95% CI: 1.18 to 1.61; p value<0.01). MR mediation analysis showed that 28.4% of the total effect of CCT on POAG risk was mediated through changes in IOP. The primary results were consistent with estimates of pleiotropy-robust MR methods. Conclusion Contrary to most observational studies, our results showed that a higher CCT is associated with an increased risk of POAG.