Detection of apoptosis in CEC. The criteria used to assess apoptosis are illustrated for CEC stained for DNA with EthD-1 (a, b, and c) and by TUNEL assay for DNA fragmentation (e, f, and g). The CEC on the left is normal and nonapoptotic, as evidenced by normal pattern of chromatin staining (a) and negative result in TUNEL assay (e). The CEC in the middle shows evidence of early apoptosis with some chromatin condensation (b) and TUNEL positivity (f). A CEC that is frankly apoptotic has marked chromatin fragmentation and condensation (c) and strong TUNEL positivity (g). These images were acquired by confocal microscopy, after which we constructed three-dimensional images from multiple sections (d and h) to highlight the difference between the nucleus of a normal (h) versus an apoptotic (d) CEC.