Mean Hb percentage and Hb content in sectors 3, 5, 8, 9, 12, 15, 19, and 21 (which mostly correspond with the outer ring of the papilla) calculated by the Laguna ONhE program were significantly lower in PD patients than in healthy controls (t-test with Bonferroni correction, P < 0.002). Here, GSTM1 is linked to Parkinson disease.