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A pain in the eye: what’s the category?

Recording electrical signals from the eye of a living mouse may become a little easier with the use of an electrode mesh that can be injected into an animal’s eye. The basic technique, as recently described1, is to perform an intravitreal injection into the rear of the eye where the mesh then unfolds onto the retina. Wires attached to the mesh and an external electrical recording device exit the eye at the lateral canthus.

The new technique was being proposed for use at Great Eastern University where Dr. Tom Villanueva, the attending veterinarian, was presenting the details of the technique to the IACUC. Dr. Brad Collins, an IACUC member, interrupted him to ask if the wires that exit from the eye are painful to the mouse. “I’ve seen videos of the surgery and aftercare” said Villanueva, “and it doesn’t appear to bother them. They don’t paw at the eye, they seem to act normally in the cage, they have normal ocular pressure and a normal pupillary reflex.”

“That may be true,” said Collins, “but if I had a wire protruding from the corner of my eye, I wouldn’t be a happy camper. I don’t know how much it would hurt, but I’ll bet it would bother me. What pain category is being proposed for this protocol?”

“USDA category D,” responded Villanueva. “The surgery is performed under anesthesia, and we will be giving buprenorphine for three days post-op.”

“Well, I’m still concerned,” Collins said. “If we believe that a procedure that’s painful or distressful to a human is likely to be painful or distressful to a mouse, then I think this should be category E, due to unalleviated distress from the wires attached to its eye and acutely altered vision from the presence of the mesh.”

“I disagree,” Villanueva answered. “As far as I know this procedure has never been performed on humans, so I don’t see how you can make that correlation. The investigator was trained on the technique at a lab where it’s being used and he knows what he’s doing, so I think it’s best to let the committee discuss the protocol and vote on it.”

If you were a member of the Great Eastern IACUC, are there additional questions you would ask? From the information currently available, which pain category do you think is appropriate for this study?


  1. 1.

    Hong, G., Fu, T.-M., Qian, M., Viveros, R. D., Yang, X., Zhou, T., Lee, J. M., Park, H.-G., Sanes, J. R. & Lieber, C. M. Science 360, 1447–1451 (2018).

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Correspondence to Jerald Silverman.

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Silverman, J. A pain in the eye: what’s the category?. Lab Anim 48, 97 (2019).

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