Verificar parte decimal de un número

'Limpia la parte decimal del número
    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        Dim z As String = "0,9990"
        Dim x As String = z.Split(",")(1)
        Dim y As Double = x / Math.Pow(10, z.Split(",")(1).Length)
        Dim n As String = y.ToString("0." + New String("#", 10))
        MessageBox.Show(n.Split(",")(1))
    End Sub