Figure 5. An example of the influence that choice of HKGs can have on the apparent changes in Tkt gene expression levels. Only data from the second time point of each treatment is shown, but is representative of that disease model, i.e., D5 for S-CorNV, D6 for CB-CorNV Balb/c and CB-CorNV C57Bl/6, D7 for CaK, AfK and PCI. The y-axis is for ratio of the Tkt expression levels in disease model corneas to that in control corneas that were obtained via direct comparison of non-normalized C_t (none) or C_t normalized using each optimal HKG or HKG pair proposed by geNorm or NormFinder, plus ACTB and GAPDH. Please note that the optimal HKGs or HKG pairs were different among models as shown in Table 4. When a HKG pair was used, the geometric means of relative expression levels against each HKG was used.