на мой взгляд...

[gavyarii.livejournal.com]

Я только изучаю... and I really cannot put many sentences together, but have been listening to Russian music and radio so I can understand much more. One phrase I hear a lot is "на мой взгляд" and I know what this means.. but why is it "взгляд" and not "взгляде", or is this for some reason accusative? Or is it some sort of idiomatic construct?

Oh and thank-you for those who added other examples, these would also be appreciated.