Night Vision: How a Cat's Eyes Function

The eyes of a cat are perhaps the most intriguing part of the feline morphology. Who has not seen the shining eyes of a cat lurking in the dark of the night? Have you wondered how the common house cat has such good vision in dim light conditions?

The answer lies in the way a cat's eye is 'built'. Those shining eyes are visible because of an extra layer at the back of each eye. This layer of reflective cells is technically called the Tapetum Lucidium. The cells are a yellowish color, and this layer of the feline eye works just like an intensely bright mirror that reflects light onto the cat's retina. In addition, cats have approximately three times more rods in their eyes when compared to people. The rod cells on the retina are used by the eye for vision in dim lighting conditions. Thus, the additional rods in the cat's eye enable its night vision to be at least six times better than our human eyes. Cats also have more nerve cells in their brains devoted to vision receptors than do humans.

The eyes of a cat also have a third eyelid. This eyelid is normally 'tucked in' at the inner corner of the cat's eye. This is called a nictitating membrane and assists in both extra protection for the eye and helps in cleaning.

A cat cannot see in complete darkness. There must be a least a low level of light for a cat's eye to have some vision. However, our eyes are so restricted in our level of night vision that we often think that a cat can see in total darkness. We do share some vision features with the cat, however. Cats, like humans, have binocular vision and peripheral vision. These features enable cats to have excellent depth perception and distance judging accuracy. These qualities of vision, coupled with the additional dim light vision capabilities enable the cat to be, to a degree, nocturnal in habit.

Cat's eyes, remarkable as they are, can be afflicted with serious problems. Cat owners should become aware of the signs of eye problems. Conjunctivitis is a serious and highly contagious (cat to cat) eye condition that manifests itself as an inflammation of the membrane that covers both the inner lining of the eyelid and the white of the eye itself. Isolate any cat with this condition from others in your household, if possible. This condition can be caused by bacterial, fungal, or viral infections. Terramycin Ophthalmic Ointment, used in the treatment of conjunctivitis,is an over the counter antibiotic available from vets or online.

Cats also share cataracts and glaucoma with their human companions. Cataracts tend to show up in elderly and diabetic cats. Veterinary diagnosis and treatment is required in cases of cataracts. Glaucoma, or excessive pressure on the interior of the eye, is the result of too little fluid drainage. Again, check with your vet for prevention and treatment.

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