I had that after a cataract operation and it was caused by extremely dry eyes.
Its awful I had to squeeze drops in every couple of hours before I could open my eye without feeling it was tearing a bit off like you have said.
1. You may have dry eyes.
2. You may have a corneal dystrophy most commonly basement membrane disorder
3. you may have scratched your cornea and it didn't heal properly.
4. You may sleep with your lids slighly open causing the cornea to dry out.
5. You may sleep under a fan or heating/cooling vent that drys the eye.
The problem is often called recurrent corneal erosions. see an Eye MD.
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