My friend got the implanon and had to get it removed because it caused her to go blind, and not be able to move her face (kind of like a stroke) and have all these other issues. She was having daily lumbar punctures to reduce her cerebrospinal fluid pressure, and they thought about putting a shunt into her brain to drain the excess fluid
but things settled a little bit. She now just has weekly lumbar punctures.
She still has no peripheral vision but her eyesight has improved a lot.
Just be wary of getting something synthetic implanted into your arm!