Excel VBA - Check if a file is open

Question

I am using this function to check if a file is open. However, it errors out with error no. 53 if the file specified as input doesn't exist. I need to add a condition, to skip the file, if it doesn't exist on the hard drive.

Public Function IsFileOpen(FileName As String)
Dim iFilenum As Long
Dim iErr As Long
On Error Resume Next
iFilenum = FreeFile()
Open FileName For Input Lock Read As #iFilenum
Close iFilenum
iErr = Err
On Error GoTo 0

Select Case iErr
Case 0:    IsFileOpen = False
Case 70:   IsFileOpen = True
Case Else: Error iErr
End Select
End Function