Transcript Senses Lab: Sight - 7th Grade Badger Team Website

Senses Lab: Sight
How do our eyes work?
Why do they work this way?
What if they don’t work correctly?
Some Background
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How does vision work?
Rods and Cones?
1 - Demonstrating the Blind
Spot
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Hold the Blind Spot Card about 18 inches from your eyes. Close
your left eye, and focus your right eye on the X, which should be
positioned so that it is directly in line with your right eye. Move
the figure slowly toward your face, keeping your right eye
focused on the X. When the dot focuses on the blind spot, which
lacks photoreceptors, it will disappear. Have your laboratory
partner record in metric units the distance at which this occurs.
The dot will reappear as the figure is moved closer.
Repeat the test for the left eye. This time close the right eye and
focus the left eye on the dot.
1- Demonstrating the Blind Spot
 P1 - Right eye: ________;
Left eye: ___________
 P2 - Right eye: ________;
Left eye: ___________
 What causes you to have a blind spot? (What is it?)
2 - Determining Near Point of
Accommodation
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To determine your near point of accommodation, hold a sharpened
pencil at arm's length in front of one eye.
Slowly move the pencil toward that eye until the pencil image becomes
distorted. Have your lab partner measure the distance from your eye to
the pencil at this point, and record the distance below.
Repeat the procedure for the other eye.
2 - Determining Near Point of Accommodation
P1
Near point for right eye: ___________________
Near point for left eye: ____________________
P2
Near point for right eye: ___________________
Near point for left eye: ____________________
 Why might two people have different near points?
 What happens to the light rays hitting the retina that causes the
blurring?
3 - Testing Visual Acuity
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Visual acuity, or sharpness of vision, is generally tested with a Snellen eye
chart, which consists of letters of various sizes printed on a white card. The
distance at which the normal eye can read a line of letters is printed at the end
of that line.
Have your partner stand the appropriate distance and as your partner reads
each consecutive line aloud, check for accuracy. If this individual wears glasses,
give the test twice – first with glasses off and then with glasses on.
Record the number of the line with the smallest-sized letters read. If it is 20/20,
the person's vision for that eye is normal. Give your partner the number of the
line corresponding to the smallest letters.
Repeat the process for the other eye.
3 - Testing Visual Acuity (without glasses / with glasses)
P1 -
Visual acuity, right eye: _______/ _______
Visual acuity, left eye: ________/_______
P2 Visual acuity, right eye: _______/_______
Visual acuity, left eye: ________/_______
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Why do you think that people lose their visual acuity as they age?
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This is the same chart
(Snellen) that your doctor
uses to determine your
visual acuity.
4 - Testing for Astigmatism
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In patients who have astigmatism, a normally spherical shaped eye is
instead slightly oval (“squished”).
The astigmatism chart on the next page tests for detects in the
refracting surface of the lens and/or cornea. View the chart first with one
eye and then with the other, focusing on the center of the chart. If all the
radiating lines appear equally dark and distinct, your refracting surfaces
are not distorted. If some of the lines are blurred or appear less dark
than others, you have at least some degree of astigmatism.
4 - Testing for Astigmatism – Is astigmatism present:
P1 - in your left eye? _________ Right eye? _____________
P2 - in your left eye? _________ Right eye? _____________
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What problems might a person with astigmatism have when trying to
converge light rays onto the retina? What would happen to the images
at which they are looking?
Astigmatism Test
Example of
Uncorrected Astigmatism
Background –
Generic Eye Diagram
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Intrinsic Muscles
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Control the lens to
allow it to focus
Control the iris to
allow more/less
light in
Extrinsic Muscles
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Attached to the
outside of the eye
moving it up/down
and left/right
Eye Reflexes
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The convergence reflex mediated by the
extrinsic eye muscles and the
accommodation reflex mediated by the
intrinsic eye muscles are described here.
The photo-pupillary reflex protects the
delicate photoreceptor cells from damage
due to excessive light and which also
involves the intrinsic muscles.
5- Accommodation Pupillary
Reflex
Have your partner gaze for approximately 1 minute at a distant object in
the lab – not toward the windows or another light source. Observe your
partner's pupils. Then hold some printed material 6 to 10 inches from
his or her face, and direct him or her to focus on it.
How does pupil size change as your partner focuses on the printed
material?
 Repeat the previous experiment, this time noting the position of your
partner' s eyeballs both while he or she is gazing at the distant and at
the close object (a pen or pencil).
Do they change position as the object of focus is changed? In what way?
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5- Accommodation Pupillary Reflex
 Describe what happens to the diameter of the pupils.
 Explain the value of this reflex. Without it, what ability of the eye would
be lost?
6 - Photopupillary Reflex
Have your partner close their eyes. After about 1 min. have your
partner remove his/her hands and watch what happens to his/her
pupils. Describe what happens to the diameter of the pupils.
6 - Photopupillary Reflex
 How does pupil size change as your partner focuses on the
printed material?
 Do they change position as the object of focus is changed? In
what way?
 Explain the importance of this reflex. What damage may come to
the eye if we didn’t have this reflex?
 Give a real-life scenario where you might observe the
photopupillary reflex.
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7 – Test for Color Blindness
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Were there any numbers you or your partner
could not see? Which ones?
Colorblind?
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is the decreased ability to perceive
differences between some of the
colors that others can distinguish.
What do things look like to those
who are colorblind?
(most common types of colorblindness)
Normal
Protanope
Deuteranope Tritanope
What do things look like to
those who are colorblind?
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Regular
Colorblind
Nothing to do with colorblind –
but cool anyway!