This is either a spelling or a pronunciation anomaly; I’m not sure which. Why is “eye” pronounced as the letter “I”?
Looking at the Etymonline entry:
c.1200, from O.E. ege (Mercian), eage (W. Saxon), from P.Gmc. *augon
the g in Old English ege would be the voiced velar fricative /ɣ/. This sound does not exist in modern English as it was palatalised to /ʝ/ and later became /j/, which we usually write with y.