Chapter 16 Hands-On Lab Cow Eye Dissection

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Hanna Heim Todd Ward BIO 2101 07 December 2023 Chapter 16 Hands-On Lab Cow Eye Dissection Introduction In this hands-on lab you will dissect and observe a cow eye. The eye specimen and the dissecting tools are in the lab kit you ordered early this semester. Make sure you watch the following videos and before starting this lab.  Safety use of scalpel : Proper Scalpel Use  How to take photographs of specimens : Photographing a Specimen  Demonstration of a cow eye dissection: Detailed Cow Eye Dissection: Part II (Jr. High, High School and College R eview) You may also choose to play this video a second time, pausing as needed, while you perform the dissection. Preparation Preview the dissection instructions on the following pages and the content on the dissection mat. For more detailed information on safety and disposal, please refer to the Mammalian Eye Dissection Investigation Manual. Follow these steps to prepare your work space: 1. Clean the work area. 2. Put on your safety glasses, gloves, and lab apron, and keep them on during dissection and cleanup. 3. Lay the pad on the work area with the white, absorbent side facing up. 4. Lay out all dissecting instruments on the pad. 5. Place the dissecting tray in the middle of the pad so that any spilled fluid will be absorbed. 6. Position the dissection mat so it is easy to reference. Page 1 of 15

Hanna Heim Todd Ward BIO 2101 07 December 2023 Dissection Photo Requirements As proof of individual work, you are required to create a Student Information Card that will be displayed in every dissection photo you take . This card should be written on a physical piece of paper/notecard and contain the following information:  Your full name  Your student S #  The date your lab is performed MM/DD/YY Important Note on Academic Honesty All labelled images must represent your own original work and may not be copied from another student or images found online. Page 2 of 15

Hanna Heim Todd Ward BIO 2101 07 December 2023 Cow Eye Dissection A. Superficial View (fatty tissue attached) Unpack the eye and place it on the dissecting tray. Use the two photos in the upper left-hand area of the front of the dissection mat as a reference. The photo on the far- left depicts an eye that is still covered in fatty tissue. The photo to the right depicts an eye that has had its fatty tissue removed. Using the dissection mat as a guide, locate each of the following structures. 1. cornea 2. sclera (if visible) 3. extrinsic eye muscle (if visible – you do not need to identify specific muscle names) 4. protective fat layer 5. optic nerve (if visible) Photograph the eye, in its original condition with all fatty tissue still connected, from a lateral view. Make sure your Student Information Card is in view. Label each of the structures listed above, and insert your labelled image in the box below. Page 3 of 15

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Hanna Heim Todd Ward BIO 2101 07 December 2023 B. Superficial View (fatty tissue removed) Use scissors and forceps to carefully remove excess superficial fatty tissue from the outside of the eye. If you didn’t watch the demonstration of a cow eye dissection on page 1, please watch this clip to see how to remove the fatty tissue: Detailed Cow Eye Dissection: Part II (Jr. High, High School and College Review). Using the photos in the upper left-hand area of the front of the dissection mat as a guide, locate the following structures. 1. optic nerve 2. sclera 3. cornea Photograph the eye from a lateral view. Label each of the structures listed above, and insert your labelled image in the box below. Page 5 of 15

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Hanna Heim Todd Ward BIO 2101 07 December 2023 C. Internal View (anterior structures) Carefully slice the fibrous outer tunic of the eye into an anterior half and a posterior half along a frontal plane, as shown on the front upper right area of the dissection mat, but cut closer to the cornea (about 1 cm away from cornea). Watch this video for an example: Eye Dissection . Do not cut deeply into the eye or squeeze it too tightly. This will help avoid damage to the delicate internal structures of the eye. It is easiest to begin the cut with a scalpel and finish with the scissors. The watery fluid that comes out as you make the incision is the aqueous humor. As you cut, notice how tough the protective sclera is. Lay the posterior half carefully to the side. Examine the interior surface of the anterior half of the eye. Photograph and label the following structures and insert your labelled image in the box below. 1. lens 2. sclera 3. ora serrata Page 7 of 15

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Hanna Heim Todd Ward BIO 2101 07 December 2023 D. The Lens Observe the lens with its attached suspensory ligaments (hard to photograph). Gently remove the lens and squeeze it between your fingers. Observe the softness of this lens compared to a camera lens. Photograph the lens . Label the lens and insert your labelled image in the box below. NOTE: If you’d like, pat the lens dry on the absorbent pad and allow the lens to dry overnight. Come back tomorrow and check the magnification on some printed text. Page 9 of 15

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Hanna Heim Todd Ward BIO 2101 07 December 2023 E. The Cornea Orient the anterior half of the eye so that the cut portion is in contact with the tray and the cornea is facing up. Gently cut out the cornea at the point where it meets the sclera, as shown on the back of the dissection mat. Lay the cornea aside and observe the iris, the darkly-pigmented ring that is revealed when the cornea is removed. Just posterior to the iris is the ciliary body , which connects the iris with the serrated tissue disk known as the ora serrata . Use forceps to gently remove the iris and ora serrata as indicated and place them on the dissecting tray. Photograph these structures next to each other (see dissection map for reference). Label the following structures, and insert your labelled image in the box below: 1. cornea 2. iris 3. ciliary body (if visible) 4. ora serrata 5. sclera (small ring) Page 11 of 15

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Hanna Heim Todd Ward BIO 2101 07 December 2023 F. Internal View (posterior structures) Pick up the posterior half of the eye (from C) and examine its internal structures. If the jelly-like vitreous humor remains in the eye, gently slip it out. Identify the retina , which contains the photoreceptor cells. If the retina rolled up in itself, do not try to move it – it is extremely delicate – just take a picture with the tapetum visible. Locate the optic disc ( blind spot ), which is the beginning of the optic nerve, often the retina is still attached to the optic nerve. Notice the darkly pigmented choroid (tapetum is part of it). Photograph the posterior half of the eye, and label the following structures, using the dissection mat as a reference. Insert your labelled image into the box below. 1. retina (might be rolled up) 2. tapetum 3. choroid 4. optic disc (blind spot) Page 13 of 15

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Hanna Heim Todd Ward BIO 2101 07 December 2023 Disposal and Cleanup 1. Dispose of any excess fluids down the drain with the water running. Allow the faucet to run for about 30 seconds to dilute the fluids. 2. Place the specimen in its storage bag and seal tightly. If you are finished working with your specimen, put the bag into an opaque trash bag for disposal in the household garbage. 3. Rinse and carefully air dry the dissection tools, and return the materials to your equipment kit. 4. Sanitize the workspace with isopropyl alcohol (or other non-bleach disinfectant) and paper towels. If this is insufficient for removing grease during cleanup, use soap and water, followed by more alcohol/disinfectant. Page 15 of 15

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Chapter 16 Hands-On Lab Cow Eye Dissection

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