Validate text box input

[CoachBarker]

I have a text box that I would like to validate the format entered.

To valiate the format of a Full Name as LastName, FirstName [MI] i do this using indexOf to check that the format is correct

 ' Check PatientFullName
If Me.txtPatientFullName.Text = "" Or Me.txtPatientFullName.Text.IndexOf(",") < 0 Then
     MessageBox.Show("The Doctors Name is mandatory and must be in the  
     format: LastName, FirstName [MI]")
     Me.txtPatientFullName.Clear()
     Me.txtPatientFullName.Focus()
Exit Sub
End If

I want to validate the format of this: Dr. FirstName LastName

I know I have to use indexOF and substrings but can't figure it out. This is what I have. I just just do not know how to figure the spaces for the First and Last Name.

 ' Check Doctors Name 
If Me.txtDoctorName.Text = "" Or Me.txtDoctorName.Text.StartsWith("Dr. ") Then
     MessageBox.Show("The Patient Name is mandatory and must be in the
     format: Dr. FirstName LastName")
     Me.txtDoctorName.Clear()
     Me.txtDoctorName.Focus()
Exit Sub
End If

Any help?

Thanks
CoachBarker