Chicken with unusual symptoms

Hi,
    My light Sussex hen had been displaying the following symptoms:
Monday evening she was fine. Tuesday morning didn't leave the coop, on further investigation, I found that she had gone blind (literally overnight). Took her to the vets, who said she had an extremely high temperature. Took her back today, temperature (even after antibiotics) was still high. She was put to sleep. Puzzling, any ideas anyone what this could have been?