Sleepies, eye gunk, eyeboogers… Whatever you call them, the proper name for that gunk that collects in the corners of your eyes is rheum. It’s exuded from your eyes while you sleep (as you know) but also your nose and mouth. When it comes from your eyes it’s primarily made of mucus discharged from your cornea or your conjunctiva. It doesn’t only happen when you’re asleep though! During the day our blinking flushes the mucus away into the nasolacrimal duct along with your tears over the Habs losing again.
If you have more rheum than most, you may be suffering from one of a few different conditions. Conjunctivitis (pink eye), chlamydia, infection of the eyelid (blepharitis) and more can all cause an excess of rheum, especially in your eyes.
If you’ve ever woken up unable to open your eye for the amount of eye goop present, you’re not alone. Not only because it’s happened to me several times, but also because it is a very common side effect of pink eye.
Dogs are dichromates whereas humans are trichromates. That means that our eyes contain 3 different types of cone cells, each of which are responsible for detecting a unique colour (for a description of both rods and cones, click here). That’s why every colour you can think of is a combination of the 3 primary colours.
But dogs only have 2 types of colour-sensing cone cells, and instead of them sensing red, blue or yellow, they’re tuned to violet and yellow-green. This means that dogs have less sensitivity in their green, yellow and red detection than humans. But conversely, humans have less sensitivity in their blue and purple detection than dogs.
And cats? Well they are a bit of a mystery. We know that they have at least two types of cone cells, one tuned to violet and one to green. But there have been studies the showed evidence of a third type of cone cell, one sensitive to light at 500 nm (greenish-blue to us). Other studies have rejected this finding, and yet others have found evidence of a cone cell sensitive at 610 nm(red to us). Currently, it’s believed they have vision similar to rhesus monkeys, called photopic trichromatic vision. In essence, they likely see similar colours to us, but not quite in the same clarity or saturation.
Cats’ and dogs’ vision systems evolved to help them hunt. They’re better at seeing movement than still objects; they see best in low light rather than bright; and they have larger visual fields (up to 270° compared to the 180° of humans!)
Cats and dogs also have evidence of their previous nictitating membranes, or third translucent eyelids, in the corners of their eyes. These would once have allowed them to maintain their sight on prey when hunting without their eyes drying out.
So when you throw a red ball into a green field, Rover sees a yellow ball being thrown into a white or gray field. Those colours just aren’t that different, so don’t be too surprised when he can’t find the ball that’s obvious to you!
Rabbits and hares are pretty cute, but they’re also fascinating.
Rabbits’ physiology is perfectly adapted for their needs. Being prey animals, rabbits need to be very aware of their surroundings. Their large ears and good hearing are well known, but did you know they also have vision that encompasses almost 360 degrees? Their eyes are situated high on the sides of their faces, giving them only a tiny blind spot directly in front of them. They even sleep with their eyes open, blinking only their nictitating membranes, or clear third eyelids, to keep their eyes moist.
Even if they can’t see or hear a predator, rabbits can probably smell them. They are obligate nasal breathers, meaning they breathe only through their noses. This way, they can always smell their environment, even when eating.
When they do smell, see or hear a predator, rabbits have to be able to make quick escapes. To help with this bunnies have very large back feet, and hinged skulls to absorb shock. Their cranial hinge allows rabbits to run at speeds above which the impact of their feet would rattle their brain around.
Remember, rabbits might be impressive, but they’re impressively bad Easter presents. Bunnies are the most abandoned pet in North America, and that’s not a statistic you want to contribute to.