Eye Dissection

EYE The eye is an extension of the brain It helps us take in light information from our surroundings. This is how!

Eye brain proximity Can you see : the optic nerve bundle? Spinal cord?

What are the parts of the eye?

Cornea- transparent membrane that covers iris and pupil Cornea- transparent membrane that covers iris and pupil. Refracts light into the eye. Clear portion of the Fibrous Tunic.

Sclera- “whites” of the eye that forms outer covering or Fibrous Tunic Sclera- “whites” of the eye that forms outer covering or Fibrous Tunic. It protects the eye & gives the eye its shape. Sclera Cornea

Can you find the fibrous tunic on your eye?

Can you find the extrinsic muscles around the eye? How many are there?

Can you find any other accessory eye structures?

Can you find the Optic Nerve? What does it do?

Why does the eye have so much Adipose connective tissue surrounding it?

Using the eye’s weight & gravity, trim all excess adipose, muscles, & accessory structures away from the eye. Leave the Optic nerve in tact. When you’re finished, your eye should look like the eye below.

1. Place the eye in the dissecting pan so the cornea is facing you. 2 1. Place the eye in the dissecting pan so the cornea is facing you. 2. Hold the eyeball gently w/your thumb & forefinger & using your scalpel, pierce the cornea just large enough for your scissors. 3. Using your scissors make a transverse cut through the cornea & then empty the Aqueous Humor from the anterior chamber of the eye onto your lab tray. Aqueous Humor is the nutritious fluid between the iris and the cornea. As we age, it breaks down and we begin to see “floaters”

Allow the aqueous humor to flow onto your tray.

Using your scalpel, pierce the sclera inferior to the cornea & iris Using your scalpel, pierce the sclera inferior to the cornea & iris. Then using scissors, carefully cut around the superior portion of the eye.. Do not squeeze the eye too tightly, so as not to push the lens &/or vitreous humor out of the eye. Lift the eye & turn it as needed to make the cut.

As you are cutting the top off of your eye, what 3 structures are you cutting through?

After completing the cut, carefully remove the front of the eye and lay it in your dissecting pan. Place the back part of the eye in the pan with the inner part facing upward.

Look @ the Internal Eye Structures – Anterior Section

Place the cornea on the hard surface of the dissecting tray (below the blue mat). Using your scalpel, make small cuts into the cornea & describe the sound it makes. It should crunch like you were cutting into an onion.

Can you see the Pupil- hole that light passes through & the Iris- colored muscle of the eye that controls the size of the pupil, thus controlling the amount of light that enters the eye. Note the oblong shape of the sheep pupil, in humans the pupil is circular. Cow Eye Iris Pupil Sheep Eye Human Eye

Using your fingers or tweezers, gently pull the Iris away from the interior, anterior portion of the eye that you just removed. Notice the color of the iris & the ciliary bodies on the edges of the iris..

Notice the Ciliary bodies on the dorsal aspect of the Iris & attached to the lens.

Ciliary Muscles- produces aqueous humor and controls lens shape Suspensory Ligament- hold the lens in place. Lens- Focuses & magnifies the image onto the retina. It is elastic so change in shape allows for focus on objects close up or far away

Separate the Lens (the marble looking structure) from the vitreous humor. Leave the vitreous humor in the tray.

Vitreous Humor- transparent jelly-like fluid that fills the posterior eye and nourishes it & holds the retina in place.

What does the Lens do?

Remove the lens and place against newspaper to see that it is a magnifier!

Retina AKA: Sensory Tunic Blind Spot- site of optic nerve connection Full of photo receptors which are sensitive to: Cones- Colour Rods- Dim light/black & white

Optic Disc is the area where optic nerve enters the retina Optic Disc is the area where optic nerve enters the retina. Can you find it? Which photo receptors are found there?

Choroid Layer- lies between the sclera and the retina & is the black layer. It provides the blood supply to the eye therefore it’s called the what layer? Tapetum lucidum- iridescent film under the retina that provides animals with “night vision”

Tapetum Lucidum

Can you identify the parts? 1. Cornea 2. Sclera 3. Optic Nerve 4. Iris 5. Pupil 6. Sclera 7. Ciliary Body 8. Choroid 9. Tapetum Lucidum 10. Retina 11. Lens 12. Vitreous Humor

Clean up! Scrape all eye parts into the trash can. Wash w/soap & water all instruments; dry them & return them to the teacher. Wash the tray & mat w/soap & water; Dry them & put them back on your table. Wipe down your table w/the table cleaner (in the spray bottles) & return your lab instructions. Wash & dry your gloves & goggles & return them to their proper place.