It’s common knowledge that it takes two eyes to see 3-dimensional images. So have you ever wondered how a one-eyed cat like Ashton gets around without bumping into things?
I know it was a concern I had when I realized she was going to lose her eye. But it’s surprising how well she compensates!
Let’s start with how most cats see.
Binocular Vision
The concept of binocular vision brings to mind a cat using a pair of field glasses. But the term binocular actually just means to see through two eyes, the way a normal cat does.
Each of your cat’s eyes sees a slightly different image because they are next to each other, and the image projected on the retina of each eye is slightly offset. Your cat’s brain puts the two slightly different images together into a single three-dimensional image.
Perceiving the three-dimensional image is called stereopsis. This three-dimensional sight helps your cat catch fast-moving prey, since they can more accurately judge distances when it’s time to pounce.
The side-to-side displacement of your cat’s eyes is easier to gauge using vertical lines and contours, which is why cats, as predators, have pupils with vertical slits.
Vertical pupils that can open wide when hunting also help maximize the contrast between the sharpness of the object your cat is focusing on and the blur of the out-of-focus objects in the foreground and background. Those also help your cat measure distance so that every pounce, whether it’s on a mouse or on a wand toy, is accurate.
Monocular Vision
Seeing with only one eye, the way Ashton does, is called monocular vision. Hearing “monocular vision” may bring to mind a cat wearing a monocle, but both monocular and monocle use the same word prefix, “mono” meaning singular.
When a cat can only see out of one eye, three-dimensional sight isn’t available to help judge how far away objects are, but there are plenty of other cues a cat can use instead:
- Focusing – Whether focusing on an object makes the eye work to focus near or far.
- Detail in objects – The texture detail of an object is more visible as an object is closer. Father objects show less detail and are more indistinct.
- Relative size – An object looks larger when it is nearer. Objects moving toward the cat look like they are growing larger.
- Light and shadow – Both light and shadow help judge the height and position of an object.
- Brightness – Closer objects appear relatively brighter than further objects.
- Motion – Nearby objects seem to move faster than farther objects when moving at the same speed. This is called as the parallax effect.
- Linear Perspective – Parallel straight lines appear to meet in the distance. The further separated the two parallel lines are, the closer the object is.
All of these are cues that a cat with two eyes uses to help judge distances to objects, too. In a sense, a cat using monocular vision only loses one of the many tools to help navigate the world.
Research and Further Reading
Annual Review of Neuroscience, The Analysis of Stereopsis
Science Advances, Why do animal eyes have pupils of different shapes?
Unviersity of Calgary, Monocular Cues
Image credits: depositphotos/RasulovS, c-foto, kuban_girl
Wow, this is all really interesting to know!
Mum just loves to come over and visit you Ashton.
It is amazing how adaptable animals can be. They never say poor me they just say okey dokey what new things can I do/learn
Hugs madi your bfff
Super interesting with terrific graphics. Thanks for explaining this. XOCK, Lily Olivia, Mauricio, Misty May, Giulietta, Fiona, Astrid, Lisbeth and Calista Jo
This is something I feel like I should’ve already known – but never crossed my mind. Thank you for sharing!
Thanks so much for the information! My 4 year old cat, Joey, is blind in his right eye, and your post explained a lot of things I never knew about cats with monocular vision.
We learned something new!
Fleurp had some issues when she was a kitten, but she over came them pretty quickly.
I also want to say, AWESOME! photos for this post.. just awesome
Very interesting ! We learned a lot ! Purrs
very interesting (and appropriate considering our conversation last week – haha)
Know a human with monocular vision. And reading about it for us is very informative. And Ashton, my mom is one of your best fans. xoxox
I agree, that really was pretty interesting!
this izza interesting post guys !!!! thanx for sharin; we R gonna tell a pal
oh ours with monocular vision, two head yur way N reed thiz !! ♥♥♥
Fascinating! Um, Ashton, you gonna bat that green mousie anytime soon?
This is a very interesting post!
How interesting to know how cats with only one eyes compensate to see.
This was very interesting. Before I was married I had a cat that lost an eye and it never slowed him up in any way. He was a prolific mouse hunter.
That was fascinating.
That’s so interesting! You’re such a special little lady, Ashton!
This is so interesting! And the pics in the post were purrfect picks, they’re great.
Excellent post, Ashton is an amazing kitty.
I’ll bet Ashton is the best hunter in your family.