Which animal has the best eyesight? - Thomas W. Cronin
The animal kingdom boasts
an incredible diversity of eyes.
Some rotate independently, while others
have squiggly-shaped pupils.
Some have protective lids,
others squirt blood.
But which creature has the best sight?
Which sees best in the darkness?
Which sees the most detail?
Which animal sees the most color?
And finally,
which detects motion the fastest?
All eyes take in sensory stimuli
in the form of waves of light.
To convert these into everything we see,
eyes focus incoming light
onto photoreceptors.
These cells translate light
into neural signals
and send them to the brain,
where they’re finally processed.
The eyes that see best in darkness
are those that capture
as much available light as possible.
Colossal squids have
soccer-ball-sized eyes—
the largest known in existence.
These may help them spot
the faint glow of sperm whales
as they disturb light-producing organisms.
Some fish have eyes that are unique among
vertebrates because they use mirrors.
For the brownsnout spookfish,
each eye has an upward-facing lens
and a downward-pointing mirror
composed of tiny crystal plates
that efficiently gather light.
They can see up and down simultaneously,
and may perceive distinct shapes,
even in the ocean’s depths.
Back on solid ground,
arctic reindeer have adaptations
to deal with months of darkness.
The backs of reindeer eyes change color,
from gold in summer to blue in winter.
Their blue-backed eyes are about
1,000 times more sensitive to light.
This may allow reindeer to recognize
important things in the snow
like urine and lichen.
When it comes to the sharpest vision,
birds of prey soar above the competition.
To capture the most detail, an animal must
have lots of photoreceptors in its eye,
as well as increased
visual processing power.
Raptors have an especially deep fovea—
a depression in the back of their eye
that fits more photoreceptors.
So, Peregrine falcons have vision that’s
more than twice as sharp as a human’s.
They’re able to zero in on a rabbit
from more than three kilometers away.
When crowning the creature
with the best color vision,
the picture gets complicated.
Different photoreceptors are sensitive
to specific waves of light,
meaning the colors we see
are largely determined
by what kinds of photoreceptors we have.
Presumably, the more types of color
photoreceptors an animal has,
the better its color vision.
Dogs have just two types.
Humans have three.
And we are far outdone
by some birds, fishes, and insects.
Bluebottle butterflies have at least
15 types of photoreceptors.
Seven of them are attuned
to distinct blues and greens,
which researchers think might help them
track each other during high-speed chases.
Mantis shrimp have a whopping
16 kinds of photoreceptors,
with five reserved just for the
ultraviolet, or UV, spectrum,
which humans can’t see.
But experiments suggest
that the mantis shrimp’s ability
to discriminate between colors
is more limited than you might expect.
Exactly how they use their complex eyes
is a mystery.
Meanwhile, with just four kinds
of color photoreceptors,
goldfish actually excel at discerning
subtle differences in shades.
Finally, insects have mastered the ability
to see the world... on the fly.
The fastest motion vision
requires photoreceptors
that quickly sense changes in light,
and a brain that rapidly
processes the information.
A movie shot at 24 frames per second
gives us the perception
of near seamless motion.
But insects would see a slideshow.
Fly photoreceptors register changes
10 times faster than we do,
making them especially hard to catch.
These animals have some
of the best vision we know of,
but there's no winner across the board.
Each category has different top contenders
because vision requires tradeoffs.
So, some eyes are highly specialized,
while others, like ours,
perform decently in many categories.
From eyes the size of soccer balls
to those that see in UV—
the ways of looking at the world
are as varied as the life forms in it.
