Using lower in create index

I've been trying to create an index on a varchar field and I've tried
using the following to create the index.

create table subject (
  name varchar(85)
);

create index subject_idx on subject using btree(lower(name) text_ops);

Gives me an error that the function lower(varchar) doesn't exist. I've
tried
placing a text(name) to force the arg to a text value, but get a syntax
error.

Anyone have Ideas on creating a lowercase index on a field that isn't
always lowercase?

Pierre