What causes the thinning of nerve fibers in the eye? Those were my results from oct.

Nerve fibers. Thin nerve fibers can sometimes be seen in glaucoma and other nerve diseases of the eye. You should take the results of an oct with a grain of salt. Although it is a very good test, the results are not always indicative of a disease, and should only be used when also taking into account your medical and eye history, as well as the results of your eye exam.
Could be normal. Thinning of the nerve fiber layer occurs in a number of disorders, most notably, glaucoma. However thinning of the nerve fiber layer can also be a normal variant. The location and pattern of the thinning can help determine this. Discuss it with your ophthalmologist.