How to read only field amount by type in Expense Claim

How to change amount field disable or enable by type in Expense Claim. Let’s say I want to disable field amount, if expense_type == “abc”. Thank you

you can hide that Field In Custom Form

Thank you for your answer, I try do by your answer eval:doc.expense_type=="abc". But if I choose another type, field amount is hidden.
I want to, If expense_type==“abc”, amount read only and if not “abc”, amount enable again.
Thank you