Is testimony valid if the witness became blind after undertaking to bear witness to an act?

Primary text

If a witness undertakes to testify regarding an act and subsequently becomes blind, it is permissible for him to testify concerning that act, provided he knows the person being testified against by name and lineage. This position is held by Al-Shafi'i. The justification is based on prior evidence and the fact that blindness is the loss of a sense that does not preclude religious obligation (taklīf). Therefore, it does not invalidate the acceptance of testimony, similar to deafness. This situation is distinct from judging, for which conditions of perfection, such as hearing and Ijtihad, are required, which are not required for testimony.