Does the patient have vision?

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When pet parents come into the clinic with a pet presenting with dilated pupils or blindness, it can be scary for the patient, client, and even the veterinary team. In an emergency, or if there is no ophthalmologist readily available to refer the patient to, is the team at your clinic up to date on how to move forward with a patient who cannot see?

During her lecture, “In the Dark: Why Is My Pet Blind,” at the 2023 New York Vet Show on November 8-9 in New York, New York, Becky Telle, DVM, DACVO, from Veterinary Eye Center of NYC reviewed with attendees the common causes of ophthalmic blindness and mydriasis in canine and feline patients, the urgency of and prognoses for these conditions, and how veterinary teams can help during such stressful moments.¹

Patient history and assessment

As with any veterinary team trying to diagnose a patient, getting the full history is crucial to understanding what is going on. Asking the pet’s parents whether the blindness came on suddenly or gradually can help determine the cause. The veterinary team can ask clients whether they noticed the blindness when the pet’s environment changed. This question can lead teams to understand that the pet has become blind gradually because it was unable to learn its new environment, causing it to bump into objects and leading owners to believe the blindness was acute.²

Once the history is noted, if the veterinary team were to call an ophthalmologist, Telle says the first thing they would ask is whether the pet has visual. To do this, Telle will utilize a maze test depending on the patient, but said just watching the animal enter the examination room can provide insights

“So, let’s go through tests of functional vision, which are the maze tests, tracking, and the menace response,” Telle said. “So, the maze test: [Sometimes] we don’t always even set up…a full maze for our patients in every situation. But you can…do this by just watching them walk into the room. How is the owner leading them? Are they on a leash? Are they carrying them—just notice their behavior before you even put your hands on the patient. Also, talk to your technicians and assistants to see how [the patient] was behaving outside in the waiting room. Those things can be really…important. And then also doing a maze test in lit rooms vs a dim room,” Telle said.

“Tracking is one that we all know: to have the tossing of balls in front of their face or dangling a string toy for the cat,” she continued. “Then the menace response that we all know and love, where you kind of move your hand toward their eye and [they’re] going to blink, that tests the cranial nerve[s] 2 and 7. Owners love to do this one, too, but they usually don't assess it correctly."

Telle explained that for the menace test, pet parents will most likely hit their pet's face unintentionally as they are moving their hand toward their eyes, causing them to blink. Instructing them how to do this properly can help you and your team get a better assessment of patients. After physical tests, if an illness or infection is suspected because of the pet’s blindness, veterinary teams can perform other tests such as blood work, x-rays, and infectious disease testing.³

Possible diagnoses

According to Telle, retinal degeneration is a progressive neurological disorder that is more common than most professionals think. For Telle and her team, the most common form of this is progressive retinal atrophy (PRA). PRA is an inherited disease that causes blindness in dogs, and it slowly progresses, beginning with a decreased ability to see well at night. Although it is not painful, there is no cure, and most dogs have adapted to their vision loss.⁴

“So, we typically see night vision blindness to start out, and then the loss of the day vision over time... as it progresses along. And then we’ll see those retinal changes [to] the tapetal hyperreflectivity, the retinal vessel attenuation, and some optic nerve atrophy. This is that…poodle, who they bring in, [and say] she’s just not seeing as well. And then [an] important question you want to ask them? Do you think there’s a difference when you turn the lights off? And almost always they’ll say, yes, she needs a night light or whatever. That’s really going to help you determine, ‘OK, we’re probably dealing with a PRA here,’” Telle said.

Pets diagnosed with PRA will commonly present with dilated pupils, abnormal reflective eyes when a light is shining on them, hesitance going downstairs, bumping into things or having clumsiness in new surroundings, not wanting to go outside or into a room if it is dark, and cataracts forming in both eyes. When it comes to PRA, genetics can play a role in whether a pet will have this disease. There is testing available for all known variants, but it is not known how many variants there are. However, some forms do not have any known genetic variants, which means a dog can develop the disease even if they were negative for known variants.

Telle also informed attendees that the loss of vision tends to be slow, which means some patients suffering from PRA may never fully go blind. From experience, she noted that smaller dogs tend to adapt better to PRA than bigger dogs, but it is still seen in bigger dogs such as Labradors.

In conclusion

Because there is no cure for PRA, management and compliance from owners is key for quality of life. Once a pet has received these diagnoses,⁴ teams can advise the family to add supplemental lighting inside and outside the home, try to limit moving furniture, block steps with safety gates, guide pets when they are in unfamiliar areas, and train the pet with verbal commands.

References

1. Telle B. In the Dark: Why Is My Pet Blind. Presented at: New York Vet Show; November 8-9, 2023; New York, NY.
2. Ofri R. Doc, will my pet see again? Assessing acute blindness. DVM360. January 6, 2020. Accessed February 15, 2024. https://www.dvm360.com/view/doc-will-my-pet-see-again-assessing-acute-blindness
3. Beal A. Blindness in dogs. PetMD.com. December 8, 2023. Accessed February 15, 2024. https://www.petmd.com/dog/conditions/eyes/blindness-dogs
4. Progressive retinal atrophy. Cornell Richard P. Riney Canine Health Center. Published September 9, 2022. Accessed February 15, 2024. https://www.vet.cornell.edu/departments/riney-canine-health-center/canine-health-information/progressive-retinal-atrophy