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Identify the different parts of the human eye and understand their functions

Identify the different parts of the human eye and understand their functions

Identify the different parts of the human eye and understand their functions
Biology Astigmatism Questions

Exercise 10: Visual Sense and the Nervous System Contemporary Biology Online Learning Objectives
• Learn the types of sensory receptors important for homeostasis
• Identify the different parts of the human eye and understand their functions
• Explain blind spot, farsightedness, nearsightedness, and astigmatism
• Perform an online colorblindness test
• Learn about the science of some optical illusions
• Test a hypothesis, analyze data and draw conclusions about visual reaction time

Materials from the Student – Internet access, yardstick or tape measure, textbook; 3–6 volunteer test subjects for the visual reaction time experiment

Introduction: The sensory nervous system receives different stimuli and sends nerve impulses to the central nervous system (the brain and spinal cord), where various parts of the brain will be alerted and will determine how to respond to maintain stable homeostasis. Our ability to touch, hear, taste, smell and see is determined by sensory receptors connected to a network of neurons communicating with our brain via the spinal cord. Scientists use different approaches to learn how receptors and neurons communicate with each other and what causes certain sensory problems, such as chronic pain, hearing loss, blindness and other conditions.

Five senses: Sight, hearing, smell, taste, touch

Types of sensory receptors that detect the internal body environment:

• Chemoreceptors detect chemicals in the environment or the blood (e.g., CO2 levels).
• Mechanoreceptors respond to touch and pressure in the skin, hair, and inner ear.
• Nociceptors detect pain, usually near the surface of tissues.
• Photoreceptors in the eye are the rods and cones. Rods detect dim light (black and white) and are located on the periphery of the retina; cones detect color and are located in the center of the retina.
• Proprioceptors detect body position and allow detailed skeletal movements.
• Thermoreceptors detect cold and heat.

This lab exercise focuses on the functional anatomy and physiology of the eye.

Anatomy of the Human Eye

Read page 289 in Chapter 11.21 of your textbook for more background facts, and visit this interactive tutorial about vision: https://www.youtube.com/watch?v=gvozcv8pS3c

Figure 1: Human Eye

In Your Blackboard Lab Report

Lab Report Question 1. Complete the following matching activity to reinforce your knowledge about the eye. (Other eye structures could be on a future lab quiz so review the basic eye anatomy.)

Eye Answer Description of the Anatomical Structures and Functions
1. Cornea C A. Light sensitive layer of cells (with rods and cones); connected to the brain via optic nerve; known as the eye’s “camera film”
2. Lens E B. Where no photoreceptors (no rods and no cones) are found; where the optic nerve exits the retina; an image on this location is not seen
3. Iris D C. Is the first to bend the incoming light into the eyes; is a clear outer covering that protects the lens and iris; can get infected or scratched
4. Retina A D. Circular muscle that controls how much light enters the eye; its pigmentation is responsible for “eye color”
5. Blind Spot B E. Flexible structure that can change its shape to focus on objects near and far; clouding of this structure results in cataract formation

Common Vision Problems

• A nearsighted person cannot clearly see objects that are located far away.

• A farsighted person cannot see objects that are very close to their eyes.

• A person with astigmatism has blurry vision because of an abnormally curved cornea. Astigmatism often occurs together with nearsightedness or farsightedness.

In Your Blackboard Lab Report

Lab Report Question 2. What causes these visual conditions? Analyze the following diagrams below to complete this online activity in Blackboard.

Eye Condition Answer Explanation
1. Astigmatism D A. Light is focused behind the retina
2. Farsightedness A B. Light is focused in front of the retina
3. Nearsightedness B C. Light is focused directly on the retina
4. Normal vision C D. Light is focused on multiple places on the retina

Thus corrective lenses are required to adjust specific vision problems.

To Learn More: Learn about Lasik Surgery http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/SurgeryandLifeSupport/L ASIK/default.htm

• Lab Activity: Visual Tests and Experiments – Record your results in this handout

• Take the Online Color Blind Test

Dr. Shinobu Ishihara developed a color perception test in 1917 to identify red-green color blindness, which is the most common type of color blindness. Lack of or dysfunctional cone photoreceptors are some causes of color blindness. The genes for the red and green visual pigments (photoreceptors) are on the X chromosome.

• Go to http://www.eyes-and-vision.com/color-blindness-test.html
• Record the numbers you can see inside each circle in the data table below. Check your answers with the website.
• IMPORTANT! If you cannot see the numbers, then you may be colorblind; however, consulting a vision care professional is recommended since this online activity is not diagnostic. Note that the results can be affected by the colors shown by the computer monitor and the lighting conditions.

Number Observed 25 6 45 8 56 29

• Visual Acuity (Ability to Focus on Sharp Details)
Proper vision includes the eyes, brain, and the visual pathways working in collaboration.
The Dutch eye doctor Dr. Herman Snellen created an eye chart in the early 1860s to measure visual acuity, or the ability to focus on sharp details. The Snellen fraction 20/20 is used to define “normal” vision but not “perfect” vision.
Generally, as the bottom number of the Snellen fraction increases, the worse the person’s visual acuity. A fraction of 20/40 indicates that someone can read at 20 feet away what a person with normal vision could read at 40 feet away.
Thus, nearsighted people without corrective lenses will have to stand closer to the Snellen chart. Sometimes one eye has a better visual acuity than the other.
Memorization of the letters on the Snellen chart may occur with repeated use of the same Snellen chart. Use a chart with different letters or numbers if a person repeats the test too often.


• First, complete the 4 online visual screening tests provided by Sterling Optical https://devlynoptical.com/online-vision-test/
• Record your observations and results in the data table provided below.

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Biology Astigmatism Questions
Biology Astigmatism Questions

Name of the Visual Test Record your online vision results

I took the test 3 times and the results weren’t sent to me, but on the screen it said that my reading power is +2.00. Left eye was at 87.5% excellent and 75% very good.

• Astigmatism: Blurred vision may occur if the cornea or lens is shaped irregularly, which prevents light from focusing properly on the retina. As a result, vision becomes blurred at any
distance. Astigmatism is a very common vision condition. Most people have some degree of astigmatism.
Optometrists use an astigmatism chart to determine if the condition is present.
No astigmatism is present if all the radiating lines appear equally dark and distinct if the refracting surface is not distorted.


Astigmatism is present (to some degree) if some of the lines are blurred and appear less dark than others.

• Focus on the center of the radiating image with each eye separately and note the appearance of the radiating lines. Did you detect astigmatism?

• Record your results (yes or no): Right eye: yes
Left eye: no

DATA ANALYSIS: Let’s review what you learned about the blind spot, colorblindness, visual acuity (Snellen fractions), and astigmatism. Please answer the following questions based on your results and the background information provided. Write in complete, coherent sentences.

Lab Report Question 3. Did you detect any form of colorblindness? And what 2 challenges do you think color-blind persons face in everyday life?

I did not detect any colorblindness in my exams. I think that 2 challenges colorblind people face in everyday life might be driving because of the stop lights and another one is not being able to cordinate colofl outfits

Lab Report Question 4. Do you have normal vision (20/20) in each eye based on the online eye exam? Compare your Snellen fraction to the normal standard of 20/20. What conclusions can you make about your results? Use this website to answer to determine your fraction. http://www.allaboutvision.com/eye-test/snellen-chart.pdf
I dont have 20/20 vision, I believe I have 20/80.

Lab Report Question 5. Which vision results did you find were unexpected or most interesting? Explain your reasons.
I have a stigma in my right eye, which I already was aware of because of my eye exams.

• Science of optical illusions

Read the BBC news article that provides fun, optical illusions and describes how scientist Beau Lotto is learning how our brain process multisensory information.
Go to http://www.bbc.co.uk/news/magazine-11553099 to see some examples.
Be sure to watch the video clip “How the brain thinks a rubber glove is a real hand,” which is an optical illusion that demonstrates neuroplasticity.

Lab Report Question 6.

a. Which optical illusion example did you like the best and why?
I like the Jungle Scene illusion becasue you cant see the animal in the black and white portion but you can clearly see it in the colored version.

To Learn More
Many more optical illusions are available at http://www.michaelbach.de/ot/

Test your ability to see afterimages: http://www.exploratorium.edu/exhibits/bird_in_a_cage/bird_in_a_cage.html

• Lab Activity: Online reaction time experiment
The human body communicates and responds to the environment using 3 types of neurons: sensory neurons, association neurons (interneurons), and motor neurons as described on textbook pages 288 – 289. To conclude this lab exercise on how the eye works and communicates with the nervous system, you will perform an experiment to test visual reaction time. A reaction time is based on
a voluntary
response, whereas a reflex is an involuntary response. A directional flow of information in a reaction response starts with the stimulus (e.g., pin prick of the finger) by the sensory receptors, which communicate
with the sensory nerves that connect to the central nervous system (CNS which is the spinal cord and brain); after which the brain sends commands to the motor neurons which control the effector responses, such as the voluntary muscles (e.g., stepping on the car brake after you see a yellow or red traffic light signal).

The faster a person responds to a visual cue (e.g., color change of a traffic light) the lower the reaction time will be in units of time (e.g., seconds). However, there are multiple factors influencing why a person might have different reaction times to the same visual cue on any given day. For example, some contributing factors to slower reactions time might be distractions (e.g., texting; loud noises), fatigue, time of day (e.g., working morning or night shifts), medications, neural disorders, vision problems, and more.

Purpose: To determine a person’s reaction time by clicking a mouse button in response to a visual cue using an online reaction test website

Question: What factors influence visual reaction time? Select an independent variable (a condition or factor) that you think will influence a person’s reaction time to a random visual signal. For example, choose to test the effect of one of the following independent variables:

• Age (older individuals vs. younger individuals)
• Time of day (morning vs. night)
• Distraction (no distractions vs. distractions present such as loud background sounds)
• Alertness
• Fatigue
• Other factor that you find relevant


• Preform the Online reaction time test . Go to http://getyourwebsitehere.com/jswb/rttest01.html
(a screen shot is provided for you on the next page so you know what to expect).

• Follow the directions for the online reaction time test in the text box provided.

Copy these online results into your lab handout to calculate the group

If you could repeat this visual reaction time experiment to get more accurate results, briefly explain what you would change and briefly explain why.
If I had to repeat this experiment again I would focus more on the big button then the green light. By that, I was starring at the green light and having a late reaction to clicking the button.

What kinds of information can you learn about a person, or a group of people, by testing their visual reaction time?
You can learn if they’re fit to drive and maybe play sports without reacting slow and getting injured.
Test Number Reaction Time
1 0.403
2 0.373
3 0.387
4 0.346
5 0.412
AVG 0.3842

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