Correlation tests of SP-A1 and CH demonstrated a significant positive relationship between the two in keratoconic eyes [mild (keratoconus) group: r = 0.366, P = 0.043; moderate group: r = 0.537, P = 0.003; severe group: r = 0.818, P < 0.001; Figure 4]. This evidence concerns the gene C4B and keratoconus.