Musannaf Ibn Abi Shayba 18:186

Abu Bakr narrated to us, he said: Muhammad ibn Bakr narrated to us, from Ibn Jurayj, he said: 'Ata' said regarding the eye: "Fifty [camels as blood money]." I said: "And if some of its vision is lost and some remains?" He said: "It is calculated according to what was lost." He said: "One covers the healthy eye, then one looks with the other. Then one covers the other, and one looks with the healthy eye, so what was lost from it is calculated." I said: "His eye became weak from old age, then it was injured." He said: "Leave it alone."