Cytochrome P450 1B1 (CYP1B1) can oxidise a variety of structurally unrelated compounds, including steroids, fatty acids, and xenobiotics as well as activating a range of procarcinogens. A specific substrate is the female sex hormone estradiol-17beta (EST17b) which is 4-hydroxylated to 4-hydroxyestradiol-17beta 4OH-EST17b). Defects in CYP1B1 can cause glaucoma disorders such as Glaucoma 3, primary congenital, A (GLC3A; MIM:231300), Glaucoma, primary open angle (POAG; MIM:137760), Glaucoma 1, open angle, A (GLC1A; MIM:137750) and Peters anomaly (PAN; MIM:604229). These disorders cause a progressive optic neuropathy characterised by visual field defects that ultimately lead to irreversible blindness (Li et al. 2011, Sarfarazi et al. 2003, Vincent et al. 2001).