The vision simulator was an invention by Doc Brown that consisted of a chair and a viewing apparatus. It allowed the viewer to view the world though the lens of an infected eye.

When Marty McFly used the vision simulator to simulate Doc's dog Einstein's vision, he noted that everything resembled cats. Thus, Doc humorously referred to this infection as cat-aracts.

The infection was cured using distilled juniper berries, which are often used to combat bacteria, so Einstein probably had a bacterial infection in his eyes.


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