Quiz: About blindness in dogs


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2 replies
  1. Sina
    Sina says:

    Thank you for this amazing website!
    I do not understand why the presented dog has an incomplete PLR on both sides. I thought that the PLR should have also been negative on both sides. It would be great if you can explain me the pathophysiology.

    • neuropetvet
      neuropetvet says:

      Hi, Sina. Thanks for the compliment!

      It is not uncommon for a functionally blind animal to have an intact PLR if they have a prechiasmal disease (i.e., retina, optic nerve, optic chiasm). Severe disease may lead to an absent PLR. However, the afferent fibers for PLR seem to be more resistant to disease than the visual pathway fibers and it only takes a few intact axons to generate a PLR. As a result, while the PLR may be abnormal, it is often still present.

      The PLR is rarely abnormal in animals with postchiasmal lesions as the afferent PLR fibers have already left this common pathway toward the midbrain.

      Hope this helps!

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