Postgres - expression index is not returning column names

[r-work]

I have the following index (example):

CREATE INDEX idx ON test_table (lower(column1))

When reading the schema, looking at test_table indexes, for that index the column name is lower (see attached screenshot).
Basically, it's neither returning the expression nor the column name.
Not sure what would be the best way to handle this, maybe just return the expression if the index is an expression?

[martinjw]

The underlying query we do is joining pg_catalog.pg_index , pg_catalog.pg_class and pg_attribute, the last gives us the attname which here is... "lower". Somehow there has to be a way to read from the pg_catalog tables that the index is a function, but that will take some research.