Previous studies have shown that a topical application of IBMX, a non-selective phosphodiesterase (PDE) inhibitor, increases tear secretion and decreases tear film osmolality through CFTR activation in dry eye patients, and that CF patients with defective CFTR exhibit tear film abnormalities more frequently than normal subjects [13,14,15]. This evidence concerns the gene ALDH7A1 and Keratoconjunctivitis sicca.