Saw the vet and she told me my horse has multiple "stuff" in his eyes that makes him unable to see in bright lights name of the condition?

Update: The vet said it wasnt serious but i just like knowing whats wrong.
Apparently whatever it is, it has nearly completely covered his 1 pupil(i believe) and he only has 1 of the stuff in his other eye.
I was just wondering if anyone knew the name of what this stuff in his eye could be?
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