What's this on her eyes?

This dark red-ish or light brown-ish stuff appears in her eyes. Maybe it's similar to what we got in our eyes when we wake up from sleep?

Is it something unusual or to be worried about? Should I take her to a vet?

This dark red-ish or light brown-ish stuff appears in her eyes. Maybe it's similar to what we got in our eyes when we wake up from sleep?

Is it something unusual or to be worried about? Should I take her to a vet?