These Unusual Cat Twins Are The Prettiest Cats On The Internet.

Think you're seeing double? Think again! These pretty kitties are blond twin sisters from Russia.

Iriss and Abyss, known together as @sis.twins on Instagram, are two blond twin sister cats based in Saint-Petersburg, Russia. Besides their beautiful white coats, you will be enchanted by their matching cases of complete heterochromia.

Complete heterochromia describes the condition in which one iris is completely different from the other. It can be hereditary, but it can also develop soon after birth. A cat with complete heterochromia is commonly referred to as an 'odd-eyed cat.'

Other types of the condition include partial heterochromia, when part of one iris is different from the rest, and central heterochromia, when the inner ring of the iris is different from the outer area.

According to the American Academy of Opthalmology, most of those born with the condition won't bear any other symptoms. In some cases, however, heterochromia may be a symptom of another condition.

It can also be acquired later in life through eye injuries, diabetes, and other causes. In the case of actress Mila Kunis, a surgery to correct her cataracts and poor vision resulted in acquired heretochromia.