Quantitative correlation between the reduction of nitroblue tetrazolium and the oxygen uptake of corneal cells

We wished to measure the amount of reduced nitroblue tetrazolium (NBT) formed in corneal cells and to relate it to the viability of the cells in terms of their oxygen uptake. Two full-thickness corneal discs of identical size (3, 4, 5 or 6 mm in diameter) were cut from the eyes of guinea pigs. One disc was processed for the measurement of its reduced NBT and cellular nitrogen content; the other was processed for the measurement of its oxygen uptake and deoxyribonucleic acid (DNA) content. As the diameter of the corneal disc (that is, the number of cells) increased, the quantity of reduced NBT, nitrogen and DNA and the oxygen uptake increased proportionality. Since each of these measures correlated positively with each other (P less than 0.01) we were able to estimate the number of viable cells in a given cornea by measuring the amount of reduced NBT (formazan granules) formed in the cells.