GSTM1 and glaucoma: Whereas some studies have found a significantly higher frequency of the GSTM1 null genotype in patients with POAG, especially in smokers compared to controls [51,52,53], others have reported increased risk with a GSTM1 positive phenotype, or in combination with a GSTT1 null genotype, [54,55] or did not find any association with the risk of glaucoma [56,57,58].