That pane doesn't actually matter*, it's a shield to stop people from fucking with the middle and outer panes.
The outer pane takes the full brunt of the cabin pressure.
You'll see a tiny hole on the middle pane (evidence of it's inability to withstand pressure cabin pressure). It's job is to 'let' the outer pane take all the pressure, while preventing moisture buildup.
*it matters in a world where people freak out and shout shit like 'I'm telling you right now, that motherfucker is not real!'
Google can suck my fat fucking graphenis