Custom field 'applies to' users or group

Hi ,

I’m working on a approval workflow project which includes 20 users and around 30 custom fields .It is required that different custom field should be visible to different users . I tried doing so by using user rights & group rights it had no effect on permission level of custom field and for now each of the user is able to view all the custom fields when a ticket is created .

Please help me with the issue .