What iphone app was used to edit this?

Let me know!

You don't say why you're assuming it's an iPhone app. It could simply be software (like Photoshop). I have not put Photoshop on my new computer, but give me just one complete photo of an eye, and I could even make that in a Word document, then capture and save it as a jpeg. All it is, is the same image staggered and piled one on top of the other. In Photoshop, it would be done in layers, then it would be flattened.

There are a few ways that could be done. It's some pretty simple editing. I've included an image I just now made without any photo editing software (or app). It's made from one image of an eye, that is put in Pages (word processing app for Mac). Then I used a capture tool (Word has one) to capture and then save it as a jpeg image. It's not perfect but just showing that special apps aren't required. Even with apps and software, working with images and graphics magical… Most of the time some knowledge working with editing images is required.