Using VIM in read-only mode as the viewer in cscope

Question

I tried setting the environment variables VIEWER/EDITOR to: '/usr/bin/vim -R', but, I got the error:
Cannot exec vim -R: No such file or directory

Is there a flag in cscope to open up files in read-only mode? Or, can the EDITOR/VIEWER be set to VIM in read-only mode? Thanks in advance!