Fig. 2. Light microscopic analysis of mitochondrial membrane function in normoxic and hypoxic human corneal epithelial cells. HCEC were cultured for 3 days in 20% (A) or 2% (B) oxygen, 5 days in 20% (C) or 2% (D) oxygen, or 7 days in 20% (E) or 2% (F) oxygen before processing for apoptosis detection using the MitoLight^TM technique. In each overlay in this Figure the green fluorescence represents cytoplasmic pools of a lipophilic cationic dye. The red fluorescence represents dye that has accumulated in mitochondria. Cells containing red-labeled mitochondria are scored as viable cells while those that lack labeled mitochondria and are uniformly green in color are scored as apoptotic. Note that at 5 and 7 days in culture, the normoxic cells appear to be smaller in size compared with the hypoxic cells.