Cat-Eyes

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Literature

Please note, that most of the literature about the anatomy of cats is in English.

Important note:
Some articles are based on experiments done with cats: We are strictly against all animal experiments, which harm the animal. But, even it is very tough to read such articles about animal experiments, they provide necessary information to understand the cat's anatomy better.

 

American Scientist Online: Helga Kolb: How the retina works 
 
Anatomy of the eyes. Note: Dogs have the same anatomy. 
 
Freie Univeristät Berlin: Diss.: Non-invasive assessment of the feline retinal morphology by OCT 
 
Georgia Veterinary Specialists, Albert Schweitzer Center: Feline corneal sequestrum 
 
Harvard Medical School, Boston: Cat colour vision, one cone process or several? 
 
HighWire Press, Stanford university: Literature list to physiology of cat eye 
 
Internet Journal of Ophthalmology and Visual Science: Ruhr university Bochum: Visual Cortex Defects in Albinos. Albinos, mainly affected are cats with Siamese points. 
 
Journal of Neuroscience: Control of Müller glial cell proliferation and activation following retinal injury 
 
Medical College of Wisconsin, Milwaukee: Color Vision. This article for dogs goes also for the cat. 
 
New York Times: Encyclopedia: Retina 
 
NIH (National Institutes of Health): Ruth Heidelberger: Synaptic transmission at retinal ribbon synapse 
 
OMIA (in NBCI) Online Mendelian Inheritance in Animals: Waardenburg syndrome 
 
Petplace.com: Protusion of the third eye lid. Articles are written by veterinaries. 
 
Red Atlas: List of eye diseases. This is a list from human ophthalmology, but the cat can have many of these diseases. Many pictures. 
 
Retina International (University of Regensburg: German partner): Retina International's Scientific Newsletter: Animal Model Database Domestic Animals 
 
The distribution of rods and cones in the retina of the cat (Felis domesticus) 
 
UC Davis: Eye diseases common in Humans and Animals 
 
University of California, Berkeley: Reconstructed movie showing animal view of world 
 
University of California, Santa Barbara: Amino Acid Signatures in the Normal Cat Retina 
 
University of California, Santa Barbara: Distribution of S- and M-cones in noraml and experimentally detached cat retina 
 
University of Erlangen-Nürnberg: Pathogenesis of glaucomas (German). This is from human medicine, but also cats may have glaucomas. 
 
University of Florida, Gainesville: Feline ophthalmology 
 
University of Leipzig, Paul-Flechsig-Institute for Brain Research. Very interesting articles about several nerve cells of the Retina (in German). 
 
University of Pennsylvania, Philadelphia: Functional Architecture of the Rode-Cone Network 
 
University of Pennsylvania, Philadelphia: Literature list with full articles. 
 
University of Sydney: A Strong Correlation Exists between the Distribution of Retinal Ganglion Cells and Nose Length in the Dog. Why should it be different in cats? 
 
University of Tübingen, Dr. Kröger: Why the cat has slit-like pupils (German) 
 
VeterinaryPartner.com: Horner's syndrome. Articles are written by veterinaries. 
 
VetMedCenter: Anatomy of the eye. 
 
Waltham: Small Animal Ophthalmology: Vision in Animals, what do Dogs and Cats see? 
 
Webvision. This is a site for human medicos, but it provides many diagrams, drawings and microscopic pictures from cats. 
 

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Cat-Eyes
Cat-Ears
Skeleton of cats
Cat-Heart
Cat-Vibrissae

The Eyes of cats

 

Eye Click on the number to get a short description.

 

Click somewhere in the picture to enlarge the picture.

What do cats see?

The cat is a nocturnal animal, thus the amount of rods (17, Retina: No 2) is much higher than that of the cones (17, Retina: No 3).

Vision field

Vision field of a cat (200° in total) is much less when compared to preys, because the cat is a predator (9, lens) and has to look into forward and downward direction when hunting. Her eyes are forward-faced and relatively large.
The vision is, compared to humans (180° in total), larger. Horses have a vision of 305°, dogs that of 250° in total.

Binocular overlapping in cats and humans is about 140°, in dogs only between 30°-60°.

Acuity

Visual acuity is the ability to see the details of an object separately and not blurred. Acuity is measured in "cycles per degree", which means how many lines one can distinguish as being separate in a degree of the visual field. Humans see 30 cycles per degree, horses 18, dogs 12 and cats 6. Acuity in cats is 0.2 times as that of humans, 0.33 as that of horses and 0.5 times as that of dogs.

Acuity

If normal humans without vision impairment have an acuity of 20/20  - i.e. an object having a distance of 20 feet can be seen sharply, then a dog has 20/75 , and a cat has between 20/100 and 20/200. That means: if normal humans can see an object sharply in a distance of 100 feet, a cat will see the same object sharply in a distance of 20 feet.

Calculation of acuity in feet is based on the method of Snellen: 1)

metric
meter
decimal Snellen
feet
   
6/3 2,0 20/10    
6/4,5 1,5 20/15    
6/6 1,0 20/20 humans
6/7,5 0,8 20/25    
6/9 0,67 20/30    
6/12 0,5 20/40    
6/15 0,4 20/50 dogs  
6/30 0,2 20/100 cats
6/60 0,1 20/200  
6/120 0,05 20/400    

Flicker rate

is the number of images per second that the image can be seen in motion and not as single images following each other.
In humans the flicker rate is lower (50 Hz) than in dogs and cats (70-80 Hz).
Usual television has a flicker rate of 60 Hz, which means dogs and cats see separated images following each other.

Such measurements are made by an ERG (electroretinography) and make sense to detect PRA or glaucoma.

Accommodation

In dogs: 2-3D (50 to 33 cm)
In cats:  4D (25 cm)
In children: 14D (7cm).
That means, cats have a relatively slow accommodation to see objects in nearer distances, a reason why they also use their other senses such as touch and smell.

Distribution of rods and cones

In cats there are about 25 rods to each cone.
Human eyes have four rods to one cone.

In cats rod density in the area centralis equals about 463,000 cones/mm2, and 250,000/mm2 on the periphery near the ora serrata.
The density of cones in the area centralis is about 27,000 cones/mm2, and 4000/mm2 in the periphery.

In humans rod density peaks at 150,000 rods/mm2 at a distance of about 3-5 mm from the foveola.
Cone density in the foveola is about 150-180,000 cones/mm2.

In dogs cone density in the area centralis is about 10,000 cones/mm2.

Note:
Cats do not have a Fovea centralis like humans, they have a streak called area centralis.

Which colours do cats see?

Distribution of S-cones and M-cones

There are 3 types of cones in humans:
S = short waved light: blue
M = medium to long waved light: yellow
L = long waved light: red

It is common sense that cats only have S-cones and M-cones (like dogs).

83%-88% of the cones in cats are M-cones, those are cones sensible for yellow.

Cats are not colour-blind, but they see their surrounding like humans, who are colour-blind for red-green, a cat cannot distinguish red colours.

For a cat the world is coloured in fuzzy pastels.
As the cat is a nocturnal animal it does not need an exact discrimination of colours.

colour vision
If the colour red is deleted from the spectrum, a cat would see the world like that.

Why do the eyes of cats glimmer in the darkness?

Cats as well as dogs have a layer behind the retina (17) called Tapetum lucidum (16). This layer works like a mirror and reflects the light rays back to the retina, thus working like an amplifier.
And that makes some sense, because the cat is a predator and is active during dawn and darkness, and must be able to recognize objects also in weak light intensities.

The Tapetum lucidum reflects the light rays back hitting it, for example light from reflectors, what we notice in the dark as glimmering of the eyes.
The tapetum also reflects flash-light when we take an image of the cat, it reflects in turquoise-blue to yellow-green and not in red as human eyes do.

There are colours in cats, where the tapetum might be degenerated or even missing, like in white cats (preferably with blue-eyes and odd-eyes), but also in cats with an extreme amount of white (like Van-cats), and also in albino-varieties which have a Siamese-pattern.
The tapetum is an important part of the cat's eyes and enables its night vision.

 
 

1) Hermann Snellen
19.02.1834, Zeist – 18.01.1908, Utrecht
Dutch ophthalmologist from Utrecht
He received his doctor's degree in 1858 at the university of Utrecht, where he was appointed as professor for ophthalmology in 1877. His scientific researches were about astigmatism, glaucoma and eye diseases.
He became famous for his eye charts, which make it possible to measure the visual acuity.

Snellen table 

Hermann Snellen
Source: Wikimedia commons
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