To observe the anatomical structures of a cow’s eye.
HOW DOES IT WORK?
The eye will be dissected to reveal certain anatomical structures that have been covered in theory. The student will look at the superficial anatomy and muscle attachments of the eye, they will then proceed to cut the eye open so that the internal anatomy of the cow’s eye can be examined. These structures include the
- aqueous humor
The lens will also be removed and examined in respect to how it is able to magnify and bend light.
- Dissection board
- Dissection scalpel and blade
- Dissection blunt-end scissors
- Metal dish
- Absorptive towels
- Latex gloves
To be supplied by the educator:
- Sheet of newspaper
- Waste bag for disposing of dissected eyes
- Cow’s eyes
- Soap, towels and warm water for hand washing
- Examine the outside of the eye. You should be able to find the sclera, or the whites of the eye. – This tough, outer covering of the eyeball has fat and muscle attached to it.
- Locate the covering over the front of the eye, the cornea. – When the cow was alive, the cornea was clear. In your cow’s eye, the cornea may be cloudy or blue in colour.
- Cut away the fat and muscle, this may only be necessary if fat is covering the cornea of the eye and is in your way. Fat around the backside of the eye can be left alone.
Flip the eye over to find the optic nerve where it exits out the back of the eye. It will be stronger and more rope-like than the surrounding fat tissue.
- Hold the optic nerve in the palm of your hand and the eye in between your index finger and thumb. Use a scalpel or scissors to make an incision in the cornea. The cornea is tougher than it appears and may require some force to puncture, be careful when using the scalpel. Once the cornea is broken, clear liquid will leak (or squirt) out – this liquid is the aqueous humor.
- Use a scalpel or scissors to make an incision in the sclera so that you can cut around the outside of the eye. Your goal is to separate the eye into a front and a back half.
- Separate the inner parts of the eye:
- The gelatinous liquid in the middle of the eye is the vitreous humor, which will also contain a hard, sphere-shaped lens.
- Find the cornea (which you punctured in step 1) and then the disk-shaped iris behind it.
- The iris will be dark in colour and contain a centre opening, the pupil.
- The image below shows how each part of the eye appears when it has been separated compare this to the components you have removed.
- The back of the eye has two layers, a very thin layer of cells that is easy to scrape off (and may fall off on its own), which is the retina. Behind, the retina is a blue, reflective layer known as the tapetum.
- The retina will converge at a point on the eye where it connects with the optic nerve. This is the optic disk. It may be easiest to find by scraping off the retina and locating the spot where it remains closely attached.
- Flipping the eye over will also show how that spot is directly in front of the optic nerve.
In the process of dissection the following anatomical structures where identified: aqueous humor, sclera, cornea, iris, pupil, vitreous humor, retina, optic nerve, blind spot and tapetum. When the lens was held up to the light the image on the other side was seen upside down, but when placed directly on a page it only magnified the image.
- Be cautions when dealing with the dissection scalpels and scissors. These items are sharp.
- When done with the experiment, wash hands thoroughly to prevent any spread of bacteria from the meat to yourself.
- If you have cuts or any flesh wounds on your hands, use examination gloves provided to prevent infection.
- Do not consume any of the left over after the dissection.