Novel Assay Assessment of Oxidative Stress Biomarkers in Patients with Keratoconus: Thiol-Disulfide Homeostasis. 
To investigate systemic oxidative stress by evaluating thiol-disulfide homeostasis using a novel automated homeostasis assay in keratoconus patients.  Twenty-eight patients with keratoconus and 30 control subjects of a similar age and gender were enrolled in the present study.  The native thiol, total thiol, and disulfide levels and the disulfide-native thiol, disulfide-total thiol, and native thiol-total thiol ratios were analyzed and compared between the keratoconus and control groups using a novel automatized spectrophotometric assay.  The median serum native thiol value was 441.5 (362.6-488.1) in the keratoconus group and 467.8 (401.8-564.6) in the control subjects.  The median serum total thiol value was 467.9 (375-580.6) in the keratoconus group and 503.3 (437.7-578.5) in the control subjects.  The median serum disulfide value was 20.1 (6.2-46.3) in the keratoconus patients and 16.7 (1.1-20.8) in the controls.  There were significant differences between the native thiol, total thiol, and disulfide levels of the keratoconus patients and controls (p = 0.001, p = 0.04, and p = 0.03, respectively) and the disulfide-native thiol, disulfide-total thiol, and native thiol-total thiol ratios of these two groups (p = 0.02, p = 0.01, and p = 0.001, respectively).  We found no significant correlation between age and any of the thiol-disulfide parameters (p > 0.05 for all values).  There is an imbalance in the systemic thiol-disulfide homeostasis in KC patients.  This metabolic imbalance may play an important role in the pathogenesis of keratoconus; thus, it can be discussed in terms of the prevention, diagnosis, and the possible treatment for keratoconus.