Hi elsa269,
I used to work in a day surgery unit where they carried out this operation. In all my time assisting with this procedure (6 months) I did not come across this happening. As the procedure is done under local anaesthetic it is imperative that the patient does not move their eye, could this have happened? Does your dad remember much about it or did he try to switch off? I think you should press the hospital for answers and dont be scared to do so. Did they give a reason for having to wait 6 months to replace the lens? It seems excessive.