My eyes are misbehaving. The morning starts clear and sharp but by mid-afternoon the computer screen grows hazy. The words in the book I’m reading begin to blur. I rub my malfunctioning orbs to clear the film that seems to coat them without success. The optometrist appointment is next week.

A human eyeball is a remarkable instrument. Among mammals human beings are creatures with truly sharp vision and  good color vision as well. We are able to distinguish fine gradations of color in the green, red, and blue spectrum. Most other mammals can see color, but cannot discriminate well between red and green. 

So how does this all work? When I open my eyes in the morning, light enters through the cornea located at the front of the eye. Behind the cornea is the colored membrane called the iris. Within the iris is the black dot known as the pupil, which in fact is a circular opening that can expand or contract to control the amount of light entering. Behind the cornea is a space filled with wobbly tissue called the vitreous humor. After passing through the pupil, light travels through the vitreous humor before striking the retina.

The retina is a marvel. It is composed of millions of light-sensitive cells known as rods and cones. Rods allow us to see in poor light, though only in black and white; cones can perceive color and fine detail. When light gets to the rods and cones, they convert its energy into an electrical signal that goes to the brain via the optic nerve. 

Seeing is a pretty complicated system and is often prone to malfunction. Myopia (nearsightedness) occurs when the  light coming through the cornea and lens focuses at a point in front of the retina rather than on it. Farsightedness or hyperopia occurs when light focuses slightly behind the retina; objects at a distance appear clear while those up close are blurry. Presbyopia happens as we grow older and muscles around the eye’s lens weaken and fail to readjust the lens’s shape from seeing at a distance to up-close vision; that’s when we start using reading glasses.

Now consider the eyes of a whale. Whales live in a world of water where color wavelengths diminish and disappear with depth. Their eyes and pupils are huge because they need to gather as many photons of light as possible to see in the water. To capture even more available light, there is a surface at the back of a whale’s eye, called the tapetum lucidum, that acts as a mirror bouncing more light to the animal’s photoreceptor cells. 

Whales do not see color, only gradations of dark and light. Some New England whales, such as humpback and right whales, often get entangled in nets, ropes and other gear related to commercial fishing. Keeping them away from such gear could reduce the number of entanglements while allowing fishermen to continue to fish. So a few years ago researchers at the New England Aquarium conducted an experiment to learn if whales could distinguish among different color ropes and thus avoid them. After recording 101 whale encounters, they found that the whales were more aware of red and orange-colored objects, which they see as high-contrast black shapes against the ocean’s background light, than objects of other colors. The scientists hypothesized that such a difference might be due in part to the fact that whales in New England waters feed upon zooplankton species that are predominantly orange-colored. 

I wonder what perception is like for a whale. Eyes on both sides of its head must give it a slightly discordant view of its watery world. And what do my, admittedly faulty, eyes perceive as I peer at my face in the mirror, at my friend’s eyes across a table, at sunlight illuminating dust motes in the dining room? The rods and cones duly stimulate my optic nerve but what, truly, do I see?