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]. The gene discussed is CFTR; the disease is cystic fibrosis.