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What does the cat see?

The cat is a nocturnal animal, thus the amount of rods (see: Retina) is much higher than that of the cones (see Retina).

Vision field

The Vision field of a cat (200° in total) is much less when compared to preys, because the cat is a predator (see: lens) and has to look into forward and downward direction when hunting.
The 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.

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:

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 glaucomas.

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, 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, that means a cat needs more rods, because it is a nocturnal animal.
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.

Hermann Snellen
1834–1908, Ophthalmologist from Utrecht

Which colors can a cat 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 color-blind, but they see their surrounding like humans, who are color-blind for red-green, a cat cannot distinguish red colors.

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

If the color red is removed from the spectrum, a cat would see the world like that.

Why do the eyes of a cat glimmer in darkness?

Cats as well as dogs have a layer behind the retina called Tapetum lucidum. 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 colors 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.

Cats are born blind

The pupil is covered by the pupillary membrane = Tunica vasculosa lentis, which is a residue from the embryonic developmental phase and disappears a few days after birth.
The eyes are sealed and will open between 9-12 days after birth.
Cats born with open eyes mostly die within the first days, they have a bad survival prognosis.
If the eyes are not opened after the 12th day, the risk of severe inflammations associated with pus is quite high. The eyes can be bathed with camomile tea to be opened, the procedure must be repeated several times between 1-2 days, because the eyes have the tendency to get sealed again.

Persisting hyperplastic Tunica vasculosa lentis
or persisting pupillary membrane (PPM) or Membrana pupillaris persistens (MPP)
In the pupillary membrane around the lens there are often residual vessels originating from the embryonic development. The vessels start at the iris and are spanned over the pupil, or even over the cornea and the lens causing cloudiness of the lens. Sometimes these vessels can be so fine that one cannot detect them without a magnifying glass. Usually these embryonic vessels degenerate and disappear within the first weeks after birth. In ill cats these vessels cause cloudiness of the lens or even may affect the vitreus body and the retina. Depending on the development of the disease it is scaled from 1-6, a scale between 2-6 shall not be used for breeding any more. There is no therapy, in some rare cases an operation of the cloudy lens might bring some improvement.
Persisting ... remaining
hyperplastic ... adenoids of mucous membrane