Protective lab gear such as goggles, aprons, and gloves
Table covering, if desired
Cutting utensils and a tray are included in the kit, however, you can order the specimen on its own if your school has scalpels and scissors on hand for you to use.
Gather materials and put on gloves, aprons, goggles, and masks. I typically require aprons and goggles, but allow gloves and masks to be optional.
Locate the fat and muscle around the eye. Using their scissors, help students remove it, informing the students that “fat cushions the eye.”
Locate the cornea on the front of the eye. Instruct that “The cornea protects the eye like a windshield.” Using the scalpel, help students to slit the cornea. Take care not to slit too deeply. “The liquid that comes out is the aqueous humor which gives nutrients to the eye. It also helps give the eye its shape.”
Locate the sclera, another protective layer. Using the scalpel, make a slit in the sclera on the side of the eye. Use the scissors to cut all the way around and remove the cornea.
Locate the iris right behind the cornea. Help students remove it. It is very thin and might come apart. That is ok. Explain that the iris is the color ring in our eye and is a muscle that can contract and expand to let in more or less light as needed to see. The pupil is in the center and although it appears black when you look in the mirror, it is simply a hole in the middle of the iris.
Remove the hard lens from the rest of the eye. Explain that it has a jelly-like substance that surrounds it. This is the vitreous humor, and it is clear so that light can pass through it. The vitreous is made up of protein and water.
Explain that the lens focuses the light in your eyes. It is soft on the outside but hard on the inside, and it grows new layers each year. If you can, look through the lens and discuss what you see. The lens also acts as a magnifier.
Remove the remaining vitreous humor from the eye. Flip the eye inside out, and notice the retina hanging from the back of the eye. Explain that it is made up of cone cells that give us central vision and help us see color (Cone = Color + Central vision + Clarity – “the 4Cs”) It is also made up of rod cells that help detect whether or not light is present.
The retina connects in one spot on the back wall of the eye, and this is known as your “blind spot” if you have vision because light cannot hit this point on the back of your eye. The vitreous pushes the retina back and makes it lay flat on the back wall of the eye. If you get folds, wrinkles, or scar tissue on the retina, your vision will be distorted. Compare to saran wrap. If you look through a flat piece, you can see through it, but once it gets crinkled, it’s hard to make out the images on the other side. Sometimes this can happen with retinal reattachment surgery.
The retina becomes the optic nerve. Find the optic nerve on the back of the eye. It is like a cable that carries information from your eye to the brain. If it’s too small or becomes damaged, the signals cannot get where they need to go.
Locate the tapetum. It is a reflective layer on the back of the eye that causes animal’s eyes to appear as though they are glowing. Humans do not have this. The back walls of our eyes are black to absorb light.
Assist students in cleaning up their materials. You can save the scalpels and scissors for reuse, but they have to be sterilized and dried with care because they rust easily.
Provide students with the Cow Eye Dissection Lab, and allow them time to answer the questions. Discuss as appropriate.
For younger students, you could do a teacher led dissection with exploration as the focus. Afterwards, you might offer the Edible Eyeball activity as an informal assessment.
Discuss the etiologies of each student’s visual impairment, correlating the impacted part of the student’s eyes to the various parts dissected from the specimen.
Encourage students to draw a diagram or write a narrative about how the eye sees.
Make a video of the student discussing each part of the eye to share with families and friends.
Research the differences between animal eyes and human eyes.