I call her Rasputin, because she's Siberian too!
That's Sasha, our oldest of three Siberian cats. Her right eye is permanently dilated--a defect from birth. We noticed it when she was a kitten, and after a visit with a vet eye specialist, realized it was a rather harmless imperfection that could not be corrected.
Frankly, you forget about it because her eyes are rather dark to begin with.
But then you snap a flash like that and see the flackback from the back of her retina and it's rather eye-catching!