Model Science the Human Eye

8/11/2019 Model Science the Human Eye

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Junior MESA Day

Model ScienceThe Human Eye


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Agenda

Overview of the Human Eye

Physiology

Functions of External Structures

Functions of Internal Structures Disorders and Diseases

Building the Model

Building the Display

Questions


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Overview of the Human Eye

Significant sense organ

Spheroid structure with an average diameter of

24mm, about 2/3 the size of a ping-pong ball

External structures: eyelids, eyelashes, tears andfat glands, extraocular muscles, conjunctiva

Internal structures: cornea, sclera, iris, ciliary

body, choroid, retina, lens, anterior and

compartment, optic nerve


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Physiology

The eye has many functions. It can distinguishlight and dark, shape, color, brightness and

distance.

Light is electromagnetic radiation at wavelengths

which the human eye can see.

A typical human eye can see wavelengths from

about 380 to 750 nm and about 790 to 400

terahertz.


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Crystalline lens Biconvex structure

Convergence of light to a nodal point

Inversion of image


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Activity 2: Focusing Images

To understand how images can be focused at onepoint

Materials: index card and push pin

1. Take index card and make a hole in the centerwith the push pin.

2. Place aside.

3. Look at a word on the wall.

4. Close your left eye and place your thumb of yourright hand in front of your right eye about 6inches away and focus your right eye on yourthumb.

5. With your left hand, now place the index cardimmediately in front of your thumb and the word


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Activity 3: Building a Refracting

Telescope

To understand that lenses cause rays of light to

come to focus by building a refracting telescope.

Safety Procedures:

Extreme caution with cutting utensils (Xacto knife, PVC pipe cutter)

Extreme caution with HOT glue gun

Materials per group:

2 standard magnifying glasses

PVC pipe

1.5 L water bottle

ruler

Shared Tools:

Glue gun and glue sticks

Flashlight

X-acto knife

PVC pipe cutter


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Functions of External Structures

Eyelids

Lubricate the eye surface by distributing tears over the

cornea

Eyelashes Stop dust and sweat from getting into the eyes

Tear Fat Glands

Keep cornea moist

Wash foreign bodies outAct as main supplier of oxygen and nutrients

Contain lysozyme


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Extrinsic / Extraocular MusclesAct to turn or rotate the eye

Conjunctiva

Lines the inner surfaces of the eyelids and continues to

cover the front surface of the eyeball, except the

cornea

vertical horizontal torsion/twisting


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Functions of Internal Structures

Fibrous Coat Cornea

Primary and most powerful

structure to focus light

Sclera

Provides protection to delicate structures,

Serves as an attachment for the extraocular muscles Helps maintain the shape of the eyeball
http://upload.wikimedia.org/wikipedia/commons/7/79/Cornea.jpg


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Vascular Coat

Iris

Thin diaphragm composed mostly of connective tissue and

smooth muscle fibers

Colored disc inside of eye which is an unique as a fingerprint

Divides the anterior chamber and posterior chamber

Pupil: regulates the amount of light passing through to the retina

Ciliary Body

Ciliary muscles serve as the chief agent in eye accommodation Ciliary processes produce aqueous humor

Choroid

Absorb excessive light

Contain network of blood vessels to supply oxygen and

nutrients


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http://upload.wikimedia.org/wikipedia/commons/1/1e/Schematic_diagram_of_the_human_eye_en.svg


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Retina Innermost layer of the eye

Receives images, comparable to the film inside a

camera

Photoreceptors Rods

Cones that absorb long-wavelength light (red)

Cones that absorb middle wavelength light (green)

Cones that absorb short-wavelength light (blue) Macula

Highest concentration of cones

Fovea centralis

Center of macula

Contains only cones and no rods


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LensA transparent cystalline biconvex structure

immediately behind the iris

Suspended from ciliary body by threadlike ligaments

called zonules Refracts light

Focuses light on the retina


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Anterior Compartment

Composed of posterior chamber and anterior chamber

Aqueous Humor

Fluid that nourishes the lens and epithelial cells

Help refract light onto the retina

Posterior Compartment

Vitreous Humor

Clear gel

Helps refract light onto the retina


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Optic Nerve

Transmits electrical impulses

from the retina to the brain

The blind spot is located at the

optic nerve head or optic disc

where there are no

photoreceptors

Retinal Blood Vessels

Arteries transmit oxygen and

nutrients

Veins carry deoxgenated blood

from the eye


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Activity 5: How Absolutely Blind is

Your Blind Spot?

Purpose: to demonstrate the extent of a studentsblind spot

If you really want to be amazed at the total

sightlessness of your blind spot, do a similar testoutside at night when there is a full moon. Cover your

left eye, looking at the full moon with your right eye.

Gradually move your right eye to the left (and maybe

slightly up or down). Before long, all you will be able to

see is the large halo around the full moon; the entire

Materials

Activity 5 sheet from curriculum (page 23)


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Activity 6: Name That Structure


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Disorders and Diseases

Astigmatism

Defect causing rays from a point to fail to meet in a

single focal point

CataractA clouding of the lens

Color Blindness

Certain colors cannot be distinguished

Conjunctivitis Inflammation or infected conjunctiva


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Dry Eye

Deficiency of any of the three layers of tear film

Glaucoma

Damage to the optic nerve

Hyperopia

Visual images come to a focus behind retina Iritis / Uveitis / Chorioretinitis

Inflammation of iris, entire uvea or choroid/retina

Myopia

Visual images come to focus in front of retina

M o r e i n f o r m a t i o n

National Eye Institute, National Institutes of Health at

http://www.nei.nih.gov
http://www.nei.nih.gov/http://www.nei.nih.gov/


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Building the Model

Model of bisected human eye < 2 ft x 2 ft x 2 ft deep and > 1 ft x 1 ft x 1 in deep

Materials

Commercial models may NOT be used

Items that are not perishable

Required Structures

Cornea, sclera, iris, ciliary body, choroid, pupil, retina,

lens, optic nerve, fovea centralis, vitreous chamber,central retinal artery, conjunctiva, and anterior chamber

Bonus points awarded for up to 4 additional

structures other than the required structures


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Building the Display

Dimensions not greater than 3 ft x 3 ft x 2 deep

Freestanding

Clearly labeled, hand-drawn or students original

computer-generated diagram of the bisected human

eye

Materials table


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Questions

Component II of competition includes anunderstanding of the anatomy and physiology of the

human eye

Randomly select 5 questions from assigned list of 22

questions (attachment to Model Science

The HumanEye Rules)

Each correct answer will be awarded up to 2 points;

partial points may be awarded for partial answers

5 unpublished tiebreaker questions available on day ofthe competition; each tiebreaker question will be worth

up to 2 points each

Documents

Model Science the Human Eye