POLG and keratoconus: Distribution of genotypes and alleles of the g.46438521G>C—NEIL1, c.2285T>C—PARP-1, c.–1370T>A—POLG, c.580C>T—XRCC1 and c.1196A>G—XRCC1 polymorphisms and odds ratio (OR) with 95% confidence interval (95% CI) in patients with KC and controls.