Musannaf Ibn Abi Shayba 18:163

Abu Bakr narrated to us, he said: Abdullah ibn Numayr narrated to us, from Muhammad ibn Ishaq, from Makhul, who said: They used to assign the [full] blood money for the two eyelids if they were removed from the eye, and that is because there is no remaining [utility] for the eye after them. If they were separated, they would assign one-third for the lower [eyelid] and two-thirds for the upper [eyelid]. And that is because it [the upper eyelid] is more protective of the eye than the lower one; it closes and shields it.