predator’s physical senses determine the manner in which it hunts. Wild
canids, for instance, favor their sense of smell – you can see this as they trot
along the hedgerows, noses in the air, reading the wind. Bears, too, lead with
their noses. Anyone who’s watched them ‘taste the air’ as they approach a
food source won’t be surprised to learn that they’re nearsighted.
With the forest cats of the Northeast – the bobcat (Lynx rufus), the Canadian lynx
(Lynx canadensis), and the once-common, now-extirpated cougar (Puma concolor)
– eyesight is the most highly developed sense, followed by sound and, lastly, smell.
This manifests in stealth. By stalking, slinking, sneaking, they position themselves for
explosive, catapulting attacks of two to five bounds within a few seconds.
A cat’s general repertoire of senses is the same as ours, and our eyes are structurally
similar. Light waves pass through the cornea, aqueous humor, pupil, lens, and vitreous
humor to the retina in that order. Functionally, their eyes, like ours, behave as a
camera with the pupillary muscles controlling the quantity and quality of light that
reaches the retina.
And yet, eons of nocturnal and crepuscular hunting have led to the evolution of
some highly specialized and adaptive ocular features. First, a cat’s field of vision is 200
degrees, as compared to a human eye’s 180 degrees. This enables cats to recognize
movement more quickly than we can. In hunting prey, avoiding detection, or escaping
predation, this is a great advantage and explains why people rarely see a wildcat while
they are walking in the woods. The cat most assuredly sees you first, allowing its
avoidance by using cover and always staying in the shadows.
Secondly, while cats’ vision in broad daylight is comparable to our own daytime
vision, in reduced- or dim-light conditions, cats see six to eight times better than we
do. This superior night vision has allowed forest cats to flourish over the millennia as
dominant – sometimes apex – mammalian predators.
Innumerable adaptations facilitate a cat’s keen night vision. The reflective yellow-green glow of a cat’s eyes when exposed to a light beam in darkness comes from a layer
of reflective cells behind the retina, called the tapetum lucidum. These cells contain
a reflective crystalline matrix of amino acids, minerals, and riboflavin (Vitamin
B2). Light that fails to be absorbed by the retina’s photoreceptor cells on first-time
exposure gets a second chance for absorption on the rebound. Thus, each photon
of light becomes two photons in dim light. (You’ll remember from science class
that the definition of a photon, where it relates to optics, is a unit of incident retinal
illumination equal to the illumination from a surface area of one square meter with the
brightness of one candle as seen through a pupillary aperture of one square millimeter
. . . or maybe you won’t; the larger point here is that humans can only imagine the
definitive visual detail these phantoms of the forest perceive as they peruse their
domain beneath a darkened forest canopy with only a trace of starlight.)
In cats, as compared to diurnal mammals, the retina’s area centralis contains a greater
number of modified dendritic photoreceptor cells known as rods. These rods are
WHAT CATS’ EYES
TELL US ABOUT
THEIR SOULS By Alcott Smith
Lynx eye: The word lynx originated from the Greek word “lychnos,” meaning “lamp” or “light;” it pertains to the
iridescence of their eyes when illuminated at night.