How was the teenager Bao Qingtian Gongsun Ce blind?

In the story of Young Bao Qingtian 2, Gongsun Ce is blind. The plot only says that he "suddenly suffered from a strange disease", so he is "blind", but it does not explain the cause, but it paves the way for the great influence of blindness on him. For example, a dialogue between Gongsun Ce and Zhan Zhao was arranged at the beginning of the story. Gongsun Ce asked Zhan Zhao what is the difference between human eyes and animal eyes, and Zhan Zhao asked Gongsun Ce whether he cherished his eyes.