Eye Dissection

Cow’s eye dissection
AIM ~
To locate and distinguish specific parts to an eye of a cow, in particular, its lens.
OBSERVATIONS ~
Before actually beginning the dissection of the cow’s eye, we were about to sketch a fairly relative picture of our observing’s of the exterior body of the eye. The eye, having almost completely being sheltered in fat and muscle, was quite firm and only the cornea and optic nerve was identified. By further cutting down the fat, we were able to spot a rather tough pinkie white outer covering of the eyeball, which we later discovered to be known as the sclera. We also noticed the blue covering over the front of the eye, known as the cornea, which became cloudy after death. Finally beginning the dissection, we made an incision in between the sclera and cornea which took much effort as it was quite tough. However once slit, a clear liquid named the aqueous humour was able to ooze out. Dissecting further, we were able to remove the lens, the iris and the pupil. The iris, suspended between the cornea and lens, came out as a rather brown coloured circle. The pupil, distinguished as the dark circle in the centre of the iris was rather quite oval. The lens was a tiny blob of white which resembled an ice capsule but however had a rather pasty soft, smooth and easily damaged texture. When splitting the eye in half, we were able to discover its rather liquid-filled chamber in which a black, jelly-like substance called the vitreous humour seeped out. Deep near the end of the inner eye with all the vitreous humour removed, was the retina. Shaped like a bowl, the light blue retina contained red blood vessels which are assumed to receive the oxygen transmitted from the blood. The eye was quite warm, considering its defrosting methods and emitted little odour which in turn suggest that its rotting stage hasn’t yet begun.

DISCUSSION ~ 1. The cornea of your eye is clear. The cornea of your dissected eye is cloudy. Why?
No oxygen via the bloodstream is being sent to the eye because the living organism’s system is dead and stops working, thus clouding it. 2. Why is it important for the cornea and lens to be clear? What would happen if it wasn’t clear?
It is very important that both the cornea and lens are clear as this allows the light to pass directly through the front of the eye to the retina. If it were black for example, the light would be restricted and without being able to see light, our vision would also be restricted. For another example, if the lens were clear but however was damaged in any fashion with maybe a scratch, what we see will also be affected. 3. In dim light, the pupil opens wide to become larger. Why is this important? What would happen if it didn’t do this?
The pupil can choose to alter its size in response to light intensity by constricting and increasing its size in the dark by dilating. If the pupil was restricted and unable to alter its size due to the luminosity rates in the external environment, we would be exposed to too much light which could make us prone to discomfort and affect our ability to see clearly. At the same time, if we were exposed to low luminosity rates without our pupil changing in size, we would not be able to see in dim light. 4. In regards to question 3, would you consider this to be an adaptation? Explain.
Yes. The pupil’s ability to adapt to the luminosity rates in our environment enables us to be able to withstand bright light and darkness. Without this adaptation, we would not be able to see in dim light and we would be prone to sight abnormalities.
Conclusion ~
Overall, the dead eye of a cow was seen to be cloudy signifying its loss of life and lack of intake of oxygen. The eye was discovered to be mostly filled with fluids of the vitreous and aqueous humour. The eye overall was discovered to be quite firm considered its shelter of fat and muscles. As such, cutting through the eye took quite an effort. It was also discovered that the eye contained another protective outer covering called the sclera. The pupil was also discovered to be able to adapt the light conditions in its environment, in which makes it possible to see in dim light and prevent damage to the eyes through emitting of high luminosities. The cornea and lens was also noted to be clear in which only then would be able to successfully pass through the cornea and lens to the retina for the image to be visually seen.

#1 LENS
The lens is a clear transparent capsule containing fibers and the cytoplasm of epithelial cells. The lens is also elastic and readily changes shape when a force is applied around its perimeter. The function of the lens is to gather incoming light and focus it on the retina. Cataract, associated with aging, occurs when the lens becomes cloudy. This condition is treated by replacing the cloudy lens with an artificial one.
#2 Cornea
The cornea is the anterior region of the outer covering of the eye. This region bulges forward and because of its transparency acts like a window. Besides transmitting light, the cornea also helps to focus the entering light rays. Astigmatism, a condition where the image is not properly focused on the retina, is caused by abnormal curvature of the cornea. Corneal grafts, depending on the availability of donated tissue, are used to treat injuries and scarring to this region of the eye.
#3 Sclera
The sclera covers the remaining 84% of the outer covering of the eye. It is composed of connective tissue and small blood vessels. In addition to providing mechanical support the sclera serves to help anchor the muscles that move the eye.
#4 Vitreous Humor
The vitreous humor fills the central cavity of the eye. It is a clear jellylike substance that helps to maintain the shape of the eye and to support the inner structures such as the retina and lens.
#5 Optic Disk (blind spot)
There are no light receptors in this region of the retina. Instead, nerve cell fibers carrying impulses from the retinal receptors leave the eye in this region and enter the optic nerve. Blood vessels continuous with the retina also enter and leave the eye through the optic disk.
#6 Optic Nerve
The optic nerve, formed from retinal nerve cell axons, transmits impulses from the light receptors of the retina to the brain.
#7 Choroid Coat
The middle layer of the eye includes the choroid coat, ciliary body and iris. The choroid coat is located just beneath the schera and is joined to it. Blood vessels travel throughout the choroid coat bringing oxygen and nutrients to the surrounding tissues. Cells making up this layer produce dark pigments that absorb excess light keeping the interior of the eye dark. In some animals, not humans, the choroid has a reflecting layer (tapetum) that causes the eye to glow when light is shined into it.
#8 Retina
The retina is the third and innermost cellular layer of the eye. It contains a highly organized and very numerous collection of light receptor cells (rods and cones) and the nerve cells associated with them. The retinal nerve cells carry sensory impulses received from the rods and cones to the neurons of the optic nerve. The surface of the retina is also covered with blood vessels that bring oxygen and nutrients to the retina and remove waste. With proper illumination and magnification a physician is able to look into the eye and observe and assess the physical condition of the vessels.
#9 Ciliary Body
The ciliary body is a thickened region of the choroid coat and forms a complete ring of tissue just anterior of the retina. Much of the tissue of the ciliary body is folded affording attachment sites for the ciliary muscles and suspensory ligaments.
#10 Suspensory Ligaments
The suspensory ligaments extend from the ciliary muscles and attach to the lens holding it in place. During usual viewing conditions, the ligaments also exert an outward pulling force on the lens causing it to be somewhat flattened. When the pulling force is reduced the elastic lens thickens and becomes more convex. This change (accommodation) occurs when you look at something close.

#11 Iris
From the outside, the iris is recognized as the colored part of the eye. It is a thin circular piece of tissue with an opening (pupil) in the center. Muscle fibers within the iris permits it to function as a diaphragm by increasing of decreasing the diameter of the pupil. Changes in the size of the pupil increases or decreases the amount of light entering the eye.
#12 Aqueous Humor
The aqueous humor, a watery substance, is secreted by the epithelial cells of the ciliary body. It first passes into the chamber between the lens and iris.and then into the space between the cornea and lens. Because secretion of aqueous humor is continuous, drainage of an equal amount of fluid is necessary to prevent the buildup of excessive internal eye pressure. This condition known as Glaucoma can result in severe pain and damage to the retina.