This looks like it was converted from an old dialect of Basic. The only thing I see as "odd" is the & Chr(8), since the check for < 32 would catch all the common Ctl chars, including Bksp, anyway. But my guess is that it was converted and modified a couple of time to end up with that. The Dim Index As Short = textBox1.GetIndex(eventSender) line looks like something left over from a previous mod or from some debugging effort. It doesn't look like Index is used at all.
CQ de W5ALT
Walt Fair, Jr., P. E. Comport Computing Specializing in Technical Engineering Software