Try the code below:

 

               If Not txtDescription.ToolControls("FontName") Is Nothing Then
                    Dim dropdown As CuteEditor.RichDropDownList
                    Dim richitem As CuteEditor.RichListItem
                    dropdown = DirectCast(txtDescription.ToolControls("FontName").Control, CuteEditor.RichDropDownList)
                    richitem = dropdown.Items(0) 'the first item is the caption  
                    dropdown.Items.Clear() 'clear the items from configuration files
                    dropdown.Items.Add(richitem) 'add the caption 
                    dropdown.Items.Add("Arial", "Arial")
                    dropdown.Items.Add("Verdana", "Verdana")                     
                    dropdown.Items.Add("Tahoma", "Tahoma") 
                    dropdown.Items.Add("<span style='font-family:Tahoma;font-size:12pt'>Tahoma</span>", "Tahoma", Tahoma") 
                End If