Refresh visible Bound only

Hi All,
I have application using GridControl and support real time data update. However, I find there has a performance issue if row count more than 500. I would like to know if it could only refresh the visible Grid instead of refresh the whole grid. I try to use GetVisibleBound to get the visible Grid for refresh. However, it always return the Bottom value as 483. So it doesn't help much.
Kindly to have all your advice.
Thanks
Derek

grid.TopRowIndex, grid.LeftColIndex, grid.VisibleLayout.LastVisibleRow and grid.ViewLayout.LastVisibleCol mark the boundaries of the visible cells in a GridControl.

Cool. It works

I am trying to refresh only the visible area as well. Sometimes the FirstRowIndex returns a wrong value. In my case it is 2 instead of 1. So, even if try to refresh the range 0 to X virtual grid is still oblivious to the request. When I set it to 1 the row still does not get refreshed.
LastVisibleRow returns 0 sometimes.