Lab Work

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  • Topic: Eye, Visual system, Retina
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  • Published : November 4, 2010
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LAB 4 – Sensory Systems

I. Vision
1. Know the types of photoreceptors in the retina. (Remember there are 3 different types of cones)

3 cones
i. Blue- short
ii. Green- Medium
iii. Yellow-Red- Long

2. Why would near point accommodation change as you get older? (Think about what happens to the lens and the muscles of the eye with age) As you get older, the lens becomes hardened.
The elasticity of the lens decreases dramatically with age, resulting in difficulty in focusing for near or close vision. (presbyopia)

3. Know what cross dominance is and why it may occur or be beneficial. Cross dominance is when your dominant eye is on the opposite side of your body than your dominant hand. This is thought to be beneficial in some sporting events, improving hand eye coordination.

4. Know what peripheral vision is, why it varies from one eye to the other, and think about why people would have different levels of peripheral vision. Also think about why certain animals need peripheral vision over others and the effects of eye placement on humans and other animals. (Are humans prey or predator? What about a horse?)

5. What is peripheral normal vision, altered focal vision, and focal vision? How did they affect your ability to “shoot” the birds in the lab? Normal peripheral vision, called visual field, for one eye is approximately 150 degrees from side to side. For both eyes, it is approximately 18- degrees.

6. Know the anatomy of the eye and the muscles that control the lens of the eye as well. (Remember those models that were out WILL be on the lab practicals)  ciliary muscles
Held in position by many strong fibers called suspensory ligaments The ciliary muscles and suspensory ligaments, along with the structure of the lens itself, enable the lens to adjust shape to facilitate focusing, a phenomenon called accommodation.

7. What is the cause of the blind spot? (Remember optical disc=blind spot) It's the spot where the optical nerve goes into the back of the eye. There are no photo receptors in this place. 

8. Be able to identify a retina slide.
9. What causes an astigmatism and how can you correct it?
This may be due to an irregular or toric curvature of the cornea or lens Irregularities in the curvatures of the lens and/or the cornea lead to a blurred vision problem called astigmatism. Cylindrically ground lenses (could be contact lenses?), which compensate for inequalities in the curvatures of the refracting surfaces, are prescribed to correct the condition.

10. Know where the olfactory bulbs (for smell, locate on bottom part of brain protected by cribiform), optic nerve, and optic chiasm are. Know the path that axon tracts follow from the retina, to the occipital lobe of the brain. Think about what would happen to your vision if specific tracts were cut along the path from the retina to the occipital lobe. What visual deficits would you experience if you cut the tract at the right or left optic nerve, optic chasm, or lateral axons extending from the occipital lobe? The optic nerve carries information from the retina to the occipital lobe of the brain, where it is ultimately processed and gives you the phenomenon of vision. The medial portions of your retinas have axons that cross over to the other side of the body at the optic chiasm, meaning that if you cut the left optic tract of the brain, you would be blind in your right visual field of your right eye, and blind in the left visual field of your left eye. You should just understand the anatomy of the visual tracts of the brain, meaning the eye, retina, optic nerves, chaism, tracts, and occipital lobes of the brain.

11. Know what causes color-blindness.What gender is most affected? Color blindness is due to a congential lack of one or more of the cone types. Inherited as an X linked condition, its far more common in males than in females. As many as 8-10% of males have some form of...
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