CCNA2 and glaucoma: The expression of p16 was found to be significantly elevated in a rat model of glaucoma, also, delineating a time point corresponding to ongoing RGC death.4 In addition, the cell cycle proteins cyclin A is expressed in reversibly damaged cells in vivo after transient focal ischemia, which regulate entry into and progression through S phase.12 RGC senescence as a phase before RGC death may refer to the expression of cyclin A, while RGCs are typically described as terminally differentiated.