What is the ruling when one who is sound in both eyes intentionally injures another's blind eye?
Chapter on Retaliation (Qawad)
Al-Mughni
Book of Wounds
Primary text
If a person with two sound eyes deliberately injures another person's eye that is already blind (a'war), the injured party is entitled to retaliation (qisas) in kind, which means the offender's sound eye is removed. Additionally, the injured party receives half of the blood money (diyah). This ruling is established by Ahmad. The rationale is that the offender has deprived the victim of all sight in that eye, and the light lost, which would command a full diyah if taken from a sound eye, cannot be fully restored by retaliation due to the impossibility of taking two eyes for one or substituting a right hand for a left. Therefore, compensation for half the lost light is necessary. Evidence is found in the general ruling of the Almighty: {And the eye for an eye} (Quran 5:45).
Supporting text
There is an alternative possibility stating that the injured party receives only the retaliation (qisas) of the existing blind eye without any additional compensation, or alternatively, accepts the full blood money as compensation, similar to the case where one cuts off a sound hand of a person whose other hand is paralyzed. This is because the 'extra value' (the potential sight in the sound eye being injured) is undifferentiated here and thus has no specific compensation, analogous to the excess quality of a sound limb over a crippled one.