Before you can use Eclipse and the Isight Design Gateway to debug an Isight extension, you must configure both for debugging.
Specify the Isight Design Gateway as an external tool for remote debugging in Eclipse as described in Configuring the Isight Design Gateway for Remote Debugging.
Specify the Isight extension that you want to debug as a Remote Java Application inside of Eclipse as described in Configuring the Isight Extension as a Remote Application in Eclipse.
If necessary, verify that the extension .jar file in the Isight library contains the most recent metamodel XML as described in Updating the Extension File.