If you use hard light from the side such as an off camera flash, you'll be able to see more detail in the ridges of the iris, you'll also be able to get rid of some of the grain and have greater DOF with brighter light.
I've taken a similar shot but it was a while ago and before I bought my macro lens... time to redo it. :)
I did have a light from the side, but it wasn't an external flash as I don't have one, just a bright desk lamp. Wish my equipment fund was bigger! :)