Autofill The Cells

I have this code present, however the autofill part needs to work by looking at the cells to the right & i dont know how to do this

Sub Merge()
Application.ScreenUpdating = False
Columns("A:A").Select
Application.CutCopyMode = False
Selection.Insert Shift:=xlToRight
Range("A10").Select
ActiveCell.FormulaR1C1 = "=IF(ISBLANK(RC[1])=TRUE,"""",RC[1]&RC[2])"
Selection.AutoFill Destination:=Range(Selection, Selection.Offset(0, -1).End(xlDown).Offset(0, 1))
Columns("A:A").Select
Columns("A:A").EntireColumn.AutoFit
Application.ScreenUpdating = True
End Sub