What can I do if my co-worker is falsely accusing me ?

What can I do if my co-worker is falsely accusing me ?
A co-worker asked me to cut some lenses for her, which I did and was very happy for her to have them even my OM states that I was very excited of the frame she chose and happy to cut her lenses, gave them to her on a Friday told her give them a try if you feel there's something wrong let me know ill help you out. Monday rolls around I am in my OM office cause my co-worker states that I have threaten her life? That the glasses where made purposely wrong, that sh couldn't see, however when the glasses where read, they match her exact prescription and PD they had been read by numerous people ( opticians & doctors) she her self (co-worker) read them and is still accusing me of such things, I come to find out that our OM called HR and I am getting written up for the incident (I was never given the HR departments number to make a claim for myself) no disciplinary action has been taken against my co-worker at all my OM said that if it persisted then she could take action. She (co-worker) has now told everyone in the office, I have yet to talk to HR since my OM has not given me the number everything has to go through her ??? I do not take lightly such accusations what can I do ?