The Oskar & Klaus blog is back! Our first post is a guest piece that tackles the topic of feline eyes and common ocular conditions, such as Oskar's microphthalmia that we're often asked about. It was created for us by Dr. Travis Strong, a knowledgeable veterinarian and animal eye surgeon; he's truly an expert in cat ophthalmology! Enjoy this picture of Oskar and read Dr. Strong's words below, and if you have additional questions, please leave them in the comments at the end.
MICROPHTHALMIA AND PHTHISIS BULBUS
Hi, my name is Travis Strong, and I'm an animal eye veterinarian based in Toronto, Canada. I want to thank Mick for extending me an invitation to provide a quick overview of some feline ocular conditions that might be of interest to the followers of Oskar's journey and now of the equally majestic Klaus.
Mick asked if I could discuss microphthalmia, as this was the presumptive ocular diagnosis in Oskar, and I think that's a great place to start. Microphthalmia means "small eye," and it ranges from extremely small, nonvisual eyes to slightly small, visual eyes. If there are only subtle changes, microphthalmic eyes might be visual, but severely small eyes are often nonvisual and have concurrent abnormalities within the eye, including cataracts and retinal detachment. Microphthalmia is more common in horses and dogs than cats, but we do rarely see it in felines. This rarity only adds to the uniqueness that was Oskar!
Generally speaking, microphthalmia occurs from one of two mechanisms during embryologic development. In the first mechanism, the optic vesicle, a balloon-like outpouching of the future brain that becomes the retina and other ocular tissues, is simply too small, leading to an eventual eye that is smaller than normal. Hereditary mechanisms are often suspected or proven to be the cause of this form of microphthalmia, although toxins and infectious causes might also be responsible in some cases. In the second form of microphthalmia, the optic vesicle might have formed normally, but the early eye doesn't form a tight seal, thus causing fluid to leak continuously out of it, leading to the inability of the eye to expand like a water balloon when being filled up. As a result, the eye remains small instead of taking on its normal size.
Microphthalmia should be differentiated from phthisis bulbus, a fun but difficult to spell and pronounce term for an eye that has shrunk secondary to chronic inflammation. Intraocular inflammation is common in cats, being induced by an array of pathologic conditions, including traumatic, infectious, and immune-mediated causes. For instance, a cat that was hit by a car leading to a traumatic ocular injury might develop severe intraocular inflammation that over time will lead to scarring and shrinking of the eye. If a cat's history is unknown, it can sometimes be rather difficult to differentiate true microphthalmia from phthisis bulbus. Many cases of presumptive microphthalmia are actually cases of phthisis bulbus, as the latter is more common, and it is possible that this might be the case for Oskar. Given that Oskar's mom had subsequent kittens with small eyes, it is more likely that true microphthalmia was the cause of Oskar's small, nonfunctional eyes.
I hope this was of some interest to you all. If it was, I'd be happy to occasionally discuss feline eyes and additional ocular abnormalities. Thank you and make it a great day!