How to get hidden passages using the eye?

Hello, I need a little bit more help. Sorry for the spam.

My problem now is, how do you get hidden passages only seen when you get the eye powerup? For example, http://i830.photobucket.com/albums/zz228/xanioz/help.png?t=1299956663 (not my level). The circled red is a passage that only appeared after I got the eye powerup. How do I get these in my own levels?

Thank you for the help!

The ghost passages are actually made of two objects. The object 17 of the ghost bank (The one that looks like a square with "XWALL" written on it) that makes the player pass trough that tile if he haves the eye. And the objects 18-21 of the ghost bank that simply serves as a visual tip of where you can pass trough the wall.

Do note, that not having the eye means you can't pass through the XWALL object.

If you don't have the eye powerup, and you use the XWALL powerup, those walls will be solid.

You can however, use the eye to mark secret passages that are always accessible, by simply not putting tiles on the 3rd layer, but on the 4th. The objects 18-21 are then only visual markers.