What can I do if my father is asked to take avastin (bevacizumab) injection for retina damage/ nerves block. Is it safe?

Safer than blindness. If Avastin (bevacizumab) has been advised, it is likely because of the presence of blinding disorder such as macular degeneration. Although there is risk with drugs injected into the eye, the risk of blindness from not treating is substantially higher. Discuss your concern with his ophthalmologist.