iPad pixel/bright spot issue

As illustrated, the screen backlight diffuser may have partially delaminated. The only remedy is replacement of the screen assembly.

You might be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to assess and test your iPad. If repair is required, you will be in the best possible place to explore your available options:

Genius Bar Reservation and Apple Support Options - Apple

Please keep us updated once your issue is solved. I am facing a similar issue on my ipad too. Its been there for atleast 2 years now. It was a large patch like yours but recently it has become normal in two bands with the patch persisting in between. If I press near the patch it appears to spread.