The eye is great but I think Pete is correct; the sharpening has been over cooked. Look at the weird halo around the left foot/leg extending up the rear end and under the tail. You can also see this effect on the top of the tit’s back. Go back to the original shot and re-apply the unsharp mask with a little less intensity. Otherwise it is a nice shot and like I said the detail in the eye is very good.
Yeah I’d agree with Noely, looks like the original exposure had to be tweaked too much. You’re better off shooting RAW, over exposing by a stop to getthe shadow detail and drawing back in the highlights when you process the RAW file.