This post was written by Shannon Falli Lasser, one of our Mountainside parents. Shannon facilitated a cow eyeball dissection lab with the Elementary students.
“Is it going to explode on us when we cut into it?!” They asked the question with nervous excitement as we embarked on our dissection journey. “No,” I assured them, “it won’t exactly explode, but there will be plenty of vitreous humor to examine once it’s opened.” This question – and others that followed – made it clear that the children were very much engaged in the lesson at hand. All were eager to get down to the serious business of cow eyeball dissection!
The children were split into small groups representing a cross-section of ages. Each group got seated in the science area of the classroom and did a quick blind spot experiment on themselves to get the ball rolling. (This was a guided experiment, consisting of holding a card with graphics in front of one eye while closing the other eye and pulling the card closer. At a specific point, one of the graphics disappeared and the brain filled the void with background information.) We then talked about how the cow eyeball is very similar in structure to the human eyeball and compared it to the structure of an insect’s eyeball… The insect eye was so unlike the human eye, it would never do as a specimen. A child posed the question: “Why does the insect have so many eyes all around, anyway?!” To which a second child replied after some thought: “…I think it has to be able to see all around in every direction because it’s, like, the primary food source of… everything!” Well said, young scientist.
Gloves on, scissors in hand, and away they went…
Their first task was to remove the periorbital fat and connective tissue around the eyeball itself. They noted the differences between fat and muscle tissue – what it looked like, how it felt, how easy it was to cut. They noted the optic nerve at the very back of the eyeball and avoided cutting it. Some children dove right into the cutting responsibilities, others chose to observe from a short distance. Still others thought they’d prefer to simply observe, but were drawn into a more active role later, after checking things out a bit.
Their next task was to make an incision posterior to the cornea and all the way around the circumference of the eyeball. At the mention of the word “cornea,” one child piped up to share her experience of scratching her cornea. The students listened intently to her details – she wore an eye patch for two weeks while it healed! It was painful then, but it’s all better now.
Once the front and rear sections of the eyeball could be separated, the children were met with their new favorite sensory experience – the vitreous humor. A gel-like substance, this prompted conversations surrounding what flavor it might be, what flavor of Jell-O they all preferred, how it looked just like egg white (was it made of the same substance?), and how they could almost feel the gel through their surgical gloves. Some moved the humor back and forth in their hands for the rest of the dissection, stopping only to make incisions and then going right back to that captivating substance.
We then examined the front half of the eyeball, noting the color of the cow’s (and our neighbor’s) iris and noting the fact that cow pupils are oval-shaped, while ours are circular. We talked about how the lens can be pulled by ligaments to change its shape and how it’s soft in life, but hard in a preserved specimen. We saw that there is aqueous humor between the lens and the cornea and that all of it is clear in a healthy, living eye to let light in, but cloudy in our specimen. “How much does a cow eyeball specimen cost?” one student wanted to know. We discussed that there are a range of prices, depending on quantity ordered, but generally far less than $5 per eyeball.
Now at the midpoint of the dissection, we moved back to the vitreous humor and removed the rest of it from the back half of the eyeball. We noticed how the retina pulled away from the back of the eye once the vitreous humor was removed. It fell away in all but one spot – the blind spot. This is where the axons of the nerve cells bundle up and travel back through the optic nerve to the brain for interpretation. (There are no photoreceptor cells here and that’s why it’s blind). This prompted conversations about what would happen if we separated a cow eye from its brain – could the eye still see? What if we transplanted a cow eye onto another brain, then what? What if we switched cow eyes and put the left one in the right one’s orbit? All good questions for follow up research!
Have I mentioned yet that one student observed every session, eagerly devouring new details? My guess is that this young scientist could have conducted the dissection without any guidance at all by the end of the three days.
The next layer we discovered was the blue-iridescent tapetum. This was a real hit for its sheer beauty! We talked about the fact that humans don’t have this layer and that it occurs in nocturnal animals and those active at dawn and dusk to aid them in night vision, reflecting the light. We peeled it off to see how thin and fragile it was. One student decided to take it home in a Ziploc bag with some vitreous humor – she wanted to see how long it would retain that color in a moist environment. Some very interesting questions came out of this layer, like: “If a human worked at night a lot, would the tapetum eventually grow to help him or her see in the dark?” “Could it evolve that way?” Hmmm…
It was clear to me that, while the children’s hands were busy with the dissection tasks of cutting and probing, their minds were thinking things through on quite another level.
Now nearing the end of the planned dissection, it was evident that some young scientists wanted to carry the research further. So, they were welcomed to bring down the dissecting microscope and look at things a bit more closely. “The lens looks like it’s made up of tiny hairs!” “The optic nerve looks like the stem of a plant!” “I see tiny critters in the vitreous humor – oh, wait, I think that’s just muck.”
Yes, this dissection got our young scientists’ minds moving. It was fun to watch and listen as they conducted their research and came up with interesting new questions and points of view. My favorite question, though, came at the end of the three days. It was while I was cleaning up the sharp dissection instruments:
“So, was that the last eyeball?” one student asked.
“Yes, just a little cleaning left and then we’ll pack it up. Did you enjoy it?” I asked.
“Yes! Can we dissect a frog next time?!” This last question was music to my ears ☺.