Figure 1. Help from one eye to its neighbouring eye.

a, The human ocular system. b, When the limbus is permanently damaged, as in the example of a patient shown, conjunctival cells invade the cornea to form a protective epithelial layer. This abnormal ‘rescue’ attempt leads to the formation of new blood vessels, chronic inflammation, stromal scarring and, finally, corneal opacity and loss of vision. c, Pellegrini, De Luca and colleagues¹ find that transplantation of corneal stem cells obtained by culturing cells taken from the limbus of the healthy eye regenerates a healthy cornea and permanently restores a patient's normal vision, as shown.