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Vet_Dr.Drea, Dog Veterinarian
Category: Dog Veterinary
Satisfied Customers: 371
Experience:  Boarded, licensed, and accredited veterinarian. Interests: general medicine, ophthalmology (eyes).
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I have a 15-year old Shih Tzu, she was a rescue. She was diagnosed

Customer Question

I have a 15-year old Shih Tzu, she was a rescue. She was diagnosed with glaucoma in her right eye, the pressure was 53 the first time. She was prescribed three eye drops, Dorzolamide 3 x daily, Timolol Maleate 2 x daily and Latanoprost 2 x daily. I have been meticulous in adhering to this schedule. After several weeks her eye pressure was 23. Last Monday, May 25, her pressure was 43 and yesterday it was 53 again. I contacted the MSU Vet. Section and took her into emergency. The ophthalmologist took her eye pressure and it was "11" - a drop of 42 from just several hours prior. I do not see/understand how the pressure could drop so drastically in such a short of time.
The ophthalmologist at MSU said he did not think she had glaucoma but a growth behind the eyeball, such as a cyst, tumor etc and suggested an MRI.
Can you give me an explanation of how the pressure could fluctuate so drastically from hour to hour, week to week? I am trying to get several other opinions before putting her through an MRI.
Thank you for any help you can provide.
Submitted: 2 years ago.
Category: Dog Veterinary
Expert:  Vet_Dr.Drea replied 2 years ago.
Hello, as a licensed veterinarian with a special interest in ophthalmology I am happy to assist you!
I know the pressure changes can seem unbelievable, but such drastic and quick changes absolutely can happen. Eye pressure is complexly regulated in the body through a balancing act of fluid production and fluid drainage, fluctuations in which can occur quickly. The medications to treat glaucoma act by either helping drainage or slowing production of fluid, and as such, can cause swings in pressure by changes the amount of fluid in the front part of the eye. These changes, either by the body or by the medications, can change the amount fluid in the front part of the eye quickly just like you can quickly change the level of water in your sink by turning down the faucet or opening up the drain. Additionally, if there is a mass behind the eye, this mass can cause changes in pressure based on how it pushes against the eye (which could be influenced by many things, for example, how she is holding her head which could change the position of the mass against her eye). I hope that makes sense!
As for whether or not to pursue an MRI, I can certainly understand your reservations and it is difficult for me to say without seeing her whether that would be my recommendation. However, I can tell you that I have personal experience with the ophthalmology team at Michigan State (I am assuming that is the school you are referring to?) and they are truly a top notch, brilliant team. I have full confidence in their abilities and would defer to their recommendation. Certainly a mass behind the eye (which is not as uncommon as it might sound) can happen, especially in an older pup like your girl, and can cause changes in eye pressure by pushing on the eye and taking up the space (the "orbit") in the skull that should be for the eye. Unfortunately, there are limited other options for getting a good image of the orbit and they are inferior, so if the suspicion is a mass there I would agree that an MRI is by far the best route to take.
As far as "putting her through" an MRI, I can tell you that MRIs are quite simple and are NOT painful or uncomfortable for the pet. They are simply like a fancy x-ray. The only difference is that to keep them perfectly still for long enough to perform the MRI, they are put under anesthesia, so there is the slight risk of anesthesia. However this risk is VERY small and MSU also has a wonderful anesthesia team that would monitor her through the entire procedure to make sure she does well under anesthesia. Since she would be under anesthesia, she wouldn't even know the MRI happened- she would simply go to sleep for a little bit and a little while later wake up and be back with you.
I hope that information helps! Please feel free to respond with additional questions or concerns. Once you are happy with my answer please remember to rate my answer so I receive credit for my time.
All the best!
Dr. Drea