Position these correctly in the center of an egg-shape and voilà! Instant realistic human.
This is possible because human eyes are nearly symmetrical within themselves. You can use the same shape for both eyes and few people will notice. Not so with other animals.
making my avatar: the eyes I was using weren’t human. Animal eyes are more akin to two teardrops pointing away from eachother, than two copies of two intersected teardrops. So, I went back to my model and tried to trace his eyes.
Turns out I suck at tracing things on the computer. I was tempted to say “screw it” and do whatever I wanted, but looking closely, the tracing had actually given me something to work with.
There are several interesting things about this tracing. The first is that, yes, mice’s eyes also have corners (the teardrop tips). However, these corners aren’t even close to being aligned (like they are in humans); they lie on a line from the nose to the ear; a line whose slope depends on the slope of the nose bridge. I also noticed that the lowest point in the line for the lower eyelid, and the highest point in the line for the upper eyelid aren’t in the center (so the thing can’t be based on a perfect circle)
Yes, I know that by showing you things from the finished drawing I’m sort of cheating. I just need you to focus on the eye, and know where it is. The vertical line marks the center, the dots are the highest and lowest points, respectively; and the diagonal line is the slope between the corners of the eye.
Now, in the real mouse, the entire eye is black, taken up by the pupil. There is no iris and no white. That is okay in the drawing if you want people to think of it as an animal, but I was trying to create a character here. People take a lot from the eyes, so I needed something more human.
I therefore forsook realism for the possibility to connect with my audience. I divided my eye into half using a circular curve, and that into half again.
I chose a couple placeholder colors: blue for the iris, black for the pupil, and a reddish-brown for the fur, and compared the effect of replacing my models head with the one I had drawn.
The fact was, my drawing was squinting slightly. This was because I had drawn along the inside of the eyelid; the eye’s line color was now serving the role of the actual eyelid, making the eye seemed more closed. I needed the mouse to open its eyes more, but the model couldn’t do that, it was a photograph. However, since I had learned how the eye was shaped, I just had to make sure to follow those rules so that it would seem like it was the actual eyelid doing it.