Eyes, Eyes, Baby - Day 2
Lesson 4 of 9
Objective: Students will understand the function of the eye and its ability to adapt.
RAP - Review and Preview
I call students to the gathering area. We talk about the previous lesson, where they watched me complete a dissection. I show them my diagram of the eye and we talk about each part and its function again.
I remind students about lab safety and we move to groups to complete our eye dissections.
It is a good idea to do a second dissection today, as well, while students do theirs in groups. I always have lots of parent helpers in the room with these kinds of activities, especially when using a razor/scalpel. These are cow eyes from a online lab supply website. Cow eyes are easy to handle as they are large. There is only one difference between a cow eye and human eye so easy comparisons are possible.
I remove the parts of the eye in the following order:
- I cut away the muscles and fat, while telling students what they do.
- I cut a slit across the cornea of the eye to release aqueous humor. This gives form to the eye.
- I cut through the sclera to cut the eye in half. The front of the eye is the cornea.
- As you open the eye from the back, you can remove the iris and show students the hole in it, that is the pupil. The pupil lets the light into the eye.
- Remove the cornea and with the iris out of the way, you can see the lens.
- Remove the lens and look through it, it shows images upside down.
- Place the lens on a piece of printed paper and the words are magnified.
- Remove the lens and the remaining goop – vitreous humor. You can now see the retina. This contains the light sensitive cells that detect light.
- The retina is attached in one spot. This is where the retina joins the optic nerve.
- The optic nerve carries messages to the brain.
- If you remove the retina, you can see a layer of blue-green. This is the tapetum, this reflects light back through the retina to increase light for night vision. We don’t have tepetum, but cats and cows do. That is why their eyes shine when light is shined on them at night.
I have students lay out each piece of the eye on a piece of paper and label it so we can talk about it after the dissection. I find, stopping and talking again about the parts of the eye, makes it difficult for younger students to complete the task. I would rather walk them through it and then go back and discuss each part.
I have students take a picture of each part of the eye so we can make a computer collage of it. I use Comic Life software to do this, but there are many ways to do this.
I call students back to the gathering area. We talk about how amazingly complex the eye is and how sensitive all those parts are. We talk about why it would be important for eyes to adapt to their environment. We talk about how light can harm vision and how animals protect themselves from taking too much light into their eyes.