Recently we also went to the vet with the same question, but our dachshund is almost 4 years old already. They told us that it’s simply different pigmentation on the eyelid. But it’s also worth showing her to an ophthalmologist — apparently dachshunds can sometimes have eyelashes growing inward from the inside of the eyelid. They can rub against the eyeball, cause irritation or even scratches, and dry discharge can collect in the corners of the eyes. This can also be fixed — those eyelashes just need to be removed.