Sulayman bin Yasar (may Allah have mercy on him) says: In a bone-exposing wound (mudihah) the head and the face are equal. If some further disfigurement also occurs in the face, an increase will be made in proportion to the disfigurement, up to half the compensation for the bone-exposing wound, and that is 25 dinars.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الديات / 16201