How can I fix blurry vision after using my iPad Air?

I reiterate my recommendation to consult your optician - as they are best qualified to offer appropriate advice.

If you believe your iPad to be defective, you might otherwise 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 test and assess your iPad. If a display fault or other defect is identified, you'll be in the best possible place to explore your available options:

Genius Bar Reservation and Apple Support Options - Apple

You would be best advised to consult your ophthalmologist/optician.

You may require eyeglasses to correct your reading vision - or, if you already wear eyeglasses or contact lenses, may need a revised prescription.