Reasons to Use the Dissection Video and Accompanying PowerPoint Presentation

Reduce the number of specimens used by a class Increase the quality of the dissection for the students Review opportunity, increasing the learning experience

for the students Student unable to dissect due to pregnancy or

hypersensitivity to the preservatives Student chooses not to dissect due to ethical/moral

reasons

Dissection 101:

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Dissection 101:

As an educator you are responsible for the implementation of the dissection activity described in the video and

PowerPoint. You must have safety procedures and rules established for your classroom and make sure all of the students follow the rules to ensure a safe environment.

South Dakota Public Broadcasting and Dakota State University cannot in any way be responsible or liable for

any injury as a result of performing the described dissection. Complete the dissection if you feel it is

appropriate and safe for your individual class. Have fun and stay safe!

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Safety Considerations

Age appropriate activity for the children in your care Material Safety Data Sheet (MSDS) available for accident

reference Poison control number/phone readily available Latex free gloves, eye protection and apron/lab coat Eyewash station, shower and sink Sharp instruments (cut away from self and others) Sharps and specimen(s) disposal Encourage students to report all accidents Basic science laboratory rules (strictly enforced)

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Dissection 101:

Cow Eye

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Exterior of the Cow Eye External Orientation

Side view

Cornea: Anterior protective covering of the eye; transparent allowing light to enter;

appears cloudy due to preservation process

Essential Fat: White/grey in color; provides protection/cushion

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Getting Started

Use a scissors or scalpel to remove the excess fat from the eyeball (capsule); always cut away from yourself

The extrinsic muscles, which are used to move the eye, should also be removed (appear marbled, similar to the look and texture of a raw steak or roast)

Do not remove the optic nerve

Dissection 101:

Cow EyeOptic nerve

Extrinsic muscles

Student Cuts:• YouTube• SDPB

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Optic nerve, chord-like structure protruding from the back of the eye; carries nervous signal from the retina to the

posterior (occipital) region of the brain

Dissection 101:

Cow Eye

Dissection 101:

Cow Eye

Continue using a scissors or scalpel to remove the fat, connective tissue and muscle from the back of the eye Clic

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Dissection 101:

Cow Eye

Use the point of a scissors or a scalpel to make an incision through the layers of the eye capsule (similar to figure 1); there are three layers from the exterior: sclera, whitish/grey, continuous with the transparent cornea, choroid, thin dark black layer and the retina, thin greyish/pink layer

Use a scissors to dissect the entire circumference of the capsule (see figure 2); do not cut toward the cornea

Figure 1 Figure 2

Student Cuts:• YouTube• SDPB

Dissection 101:

Cow Eye

Using steady pressure, pull the two sections slowly apart Click

Vitreous humor: Jelly-like material, provides

shape/support for the eyeball; helps hold retina in place

Dissection 101:

Cow Eye

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Many times the greyish/pink retina is attached to the vitreous humor, carefully remove/scrape the retina from the vitreous

humor and lay it on the back of the eyeball. Click

Vitreous humor removed, retina against the

back of the eyeStudent Cuts:

• YouTube• SDPB

Using your finger or a forceps, carefully scrape any of the jelly-like vitreous humor that is attached to the front of the eye

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Dissection 101:

Cow Eye

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Retina: Nervous tissue, location of the photo receptors (cones for sharp color vision and rods for night, dark/shaded vision); light energy converted to electrical impulse; the retina is continuous

with the optic nerve which leaves the back of the eye carrying the nervous impulse to the brain

Dissection 101:

Cow Eye

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Retina

Optic nerve

Optic disc (blind spot): location on the retina where the retina attaches to the optic nerve, sight does not occur at this

location because there are no cones or rods present

Dissection 101:

Cow Eye

Many laboratory books label the fovea centralis/macula, which is the location in eye where the sharpest vision occurs; the fovea centralis/macula

is dense with cones and is the location of focus during lighted conditions, like reading; the fovea centralis/macula appears as a depression in the

retina, but it is very difficult to find(Note: know the function for the quiz, identification is not required )

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Dissection 101:

Cow Eye

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Choroid: Dark layer of the eye, rich with blood vessels; reduces

scattering of light and provides nourishment for the eye

Choroid shown folded forward in this image

Many vertebrates like the cow, deer and cat have a tapetum lucidum which is an iridescent, reflective layer found on the choroid; the

tapetum lucidum aids in the reflection of light toward the retina, increasing the ability to see at

night; the human choroid does not have a tapetum lucidum

Dissection 101:

Cow Eye

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Sclera: Tough protective outer layer of the eye which gives the eyeball its shape; the white part of the human eye; continuous with the transparent cornea; the sclera has blood vessels (may

appear bloodshot); the cornea does not have blood vessels

Cornea

Dissection 101:

Cow Eye

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Anterior Identification

Using a dissection probe, carefully remove the lens from the anterior of the eye

Lens

Suspensory ligaments: Hold the lens in place, attaches

lens to ciliary body

Note: Aqueous humor, a transparent fluid produced by the

ciliary body is located between the lens and the cornea; the fluid provides shape for and nourishes

the cornea and it also provides nourishment for the lens; the fluid will release as the lens is

removed

Student Cuts:• YouTube• SDPB

Dissection 101:

Cow Eye

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Using a dissection probe, carefully remove the choroid, ciliary body, and iris from the anterior of the eye; these structures will be removed as one unit

Dissection 101:

Cow Eye

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Cornea: Anterior protective covering of the eye; transparent allowing light to enter; appears cloudy due to preservation process; lacks blood vessels, nourished by aqueous humor;

continuous with sclera

Dissection 101:

Cow Eye

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Lens: Biconvex structure that focuses light on the retina through a process called accommodation

Dissection 101:

Cow Eye

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Lens

Lens

Far Object

Close Object

Retina

Retina

Muscles of the ciliary body contract toward the lens (Figure 1), resulting in less pull on the lens. The lens bulges to its natural form resulting in the light rays bending more for closer objects. The muscles of the ciliary body relax pulling away from the lens causing the lens to flatten for distant objects (Figure 2).

Ciliary Body

Iris

Pupil

Figure 2

Figure 1

Dissection 101:

Cow Eye

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Iris: Structure of the eye which controls the size of the opening into the eye which is called the pupil. The pupil gets larger when the radial

muscles of the iris contract in dim light. The circular/sphincter muscles of the iris contract to reduce the size of the pupil for brighter light. The

iris is the colored structure of the human eye.

Pupil: Opening of the eye, allows light to enter. The diameter of

the opening is controlled by the iris. The pupil is the dark center

of the eye; the pupil is black because light enters but it does

not leave.

Ciliary body

Dissection 101:

Cow Eye

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Microscopic View of the Iris, Ciliary Body and Pupil

Anterior view, closest to the cornea Posterior view, closest to the lens

Ciliary bodyIris

PupilPupil

Dissection 101:

Cow Eye

Retina

Optic nerve

Choroid with tapetum lucidum

Iris Pupil

Cornea

Sclera

Lens

Vitreous humor Click

Review Main Structures

Dissection 101:

Produced by Dakota State University and South Dakota Public Broadcasting

Cow Eye