Thread: Creating case insensative Index

I am receiving  the following errors on creating an index using lower() on a
varchar field

db1=> create index fieldindexlower on table1(lower(fieldvalue) varchar_ops);
ERROR:  BuildFuncTupleDesc: function 'lower(varchar)' does not exist


Do I need to convert the field to "text" or are there other options ?

Thanks,
Vince