Ibn al-Musayyib (may Allah have mercy on him) said regarding the eye of a one-eyed man: If his remaining eye is put out deliberately, there is retaliation (qisas), and no more than one eye like it is taken in retaliation; if he accepts blood money for it, then there is the full blood money, because it is all that remains of his sight.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16297