1. Activity Overview
Create and characterize an image on the “retina” of the human eye model.
Understand the function and limitation of the adaptive lens in the human eye.
Examine the effect of the aqueous and vitreous humor on the focal length of the eye lens.
Simulate far sightedness on the eye model and how to correct it with eye glasses.
Understand the effect of the pupil.
Simulate near sightedness on the eye model and how to correct it with eye glasses.
Simulate astigmatism and use corrective eye glasses for it.

2. The Eye Model – Top View Slots for “eye glasses” “Cornea”
“Retina” (in “Normal” position)
Slots for “eye lenses”

3. The Inserting Lenses In front of “cornea” for “eye glasses”
Behind “cornea” as “eye lens”

4. The Lens Set
“Astigmatism” lenses have slots indicating axis of cylindrical lens.
“Pupil”
6 lenses

5. Lens Care (lenses are made of polycarbonate)
When not in use: Always place lenses back into slots in the pink foam.
Do not place lenses on the table (They get scratched easily)
Do not “clean” lenses with paper towels etc..
When lenses are dirty: Rinse with water and let air dry.

6. The Adaptive Lens
Syringe
“Pupil”

7. Filling the Adaptive Lens
Get some clean water from the filtered drinking fountain in the hallway (our regular tap water has rust sediments – avoid using it in this lab).
Disconnect the syringe from the hose and partially fill it with water.

8. Filling the Adaptive Lens
Connect partially filled syringe to tube and lens again
Lens should hang down from tube
Pull syringe piston outward to suck air out of lens (you should see bubbles rising through the water in the syringe).

9. Filling the Adaptive Lens
Alternate between pushing some liquid down into the lens and pulling the syringe up to remove air bubbles until lens is filled with water and there is very little (or no) air left in the lens.

10. Emptying the Adaptive Lens
Once you are finished using the adaptive lens, please remove the water again as follows:
Hang syringe downward and lens on top.
Pull syringe piston up and down a bit to suck water from the lens and push air into it.
Empty syringe as needed and repeat the above step until the lens is empty.
Store the lens in the plastic bag so it won’t get scratched.

11. Activity 1: Characterizing the image formed on the retina
Only the cornea lens is used in this activity.
Analyze retina picture orientation
Analyze cornea lens properties
Retina Screen
Cornea Lens
Eye Model
Optics Track
Eye Model Bracket

12. Activity 2: The effects and limits of the adaptable crystalline lens
Add 400mm lens as an example of adaptable crystalline lens at its longest focal length.
Analyze effect of 400mm lens on retina image and overall focal length of lens system (cornea plus 400mm lens).
Repeat with 120mm lens as an example of adaptable crystalline lens at its shortest focal length.
Finally, use the water-filled adaptive lens to simulate an adaptable lens in the human eye.
400mm lens
then 120mm
then adaptable lens

13. Filled with clean water
Activity 3: The effects of the aqueous and vitreous humor on the focal length
Fill eye model with clean water (use filtered water from drinking fountain in hallway)
Analyze the effect of the water on the overall focal length of the lens system.
Use 62mm and 120mm lenses for “adaptive lens” extreme values.
With 62mm lens find “near point” of eye model.
Filled with clean water

14. Activity 4: Simulating a Far Sighted Eye
Move retina screen to “Far” position (slot closer to the “cornea”) to simulate a shorter than normal eyeball causing far-sightedness.
Determine the new “near point” under this condition.
Fit “reading glasses” (placed in the slots in front of the cornea) for this eye to correct the near point deterioration experienced by this condition.
Retina screen in “Far” position

15. Activity 4: Simulating a Far Sighted Eye
Normal near point
Image on retina is much smaller (can’t read it) A A
Near point of far sighted eye

16. Activity 4: Simulating a Far Sighted Eye
Normal near point
Eye looks at the virtual and enlarged image of text at near point.
Text at normal distance but within focal length of reading glasses
Reading glasses A A
Image on retina is larger again A f
Near point of far sighted eye

17. Activity 4: Simulating a Far Sighted Eye
Object distance = normal near point distance A
so=dnormal A A
si=dold
Image distance = far sighted near point distance
1 𝑓 = 1 𝑠 𝑜 𝑠 𝑖 → 𝑓 = 1 𝑑 𝑛𝑜𝑟𝑚𝑎𝑙 −𝑑 𝑜𝑙𝑑 →𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒 𝑓

18. Activity 4: Simulating a Far Sighted Eye
Farsightedness means the near point is farther away from the eye than usual
 to see a sharp image of printed text, for example, the text would have to be held further away
 text image appears too small on retina.
Reading glasses for people with far sighted eyes

19. Activity 5: The effect of the pupil
Analyze the effect of the pupil on image sharpness and brightness.
Pupil inserted in front of lens (round pupil down)

20. Activity 6: Simulating a near sighted eye
Move retina screen to “Near” position (slot furthest from the “cornea”) to simulate a longer than normal eyeball causing near-sightedness.
Determine the “far point” under this condition.
Fit “eye glasses” (placed in the slots in front of the cornea) for this eye to correct the far point deterioration experienced by this condition.
Retina screen in “Near” position

21. Activity 6: Simulating a near sighted eye
Normal far point = “infinite” distance A ∞
Near sighted eye far point = reduced distance A
𝑑 𝑓𝑎𝑟

22. Activity 6: Simulating a near sighted eye
Eye glasses (diverging lens)
Virtual image at the far point
Object far away A A
𝑠 𝑜 =object distance=∞
𝑠 𝑖 = 𝑑 𝑓𝑎𝑟
1 𝑓 = 1 𝑠 𝑜 𝑠 𝑖 → 𝑓 = 1 ∞ + 1 −𝑑 𝑓𝑎𝑟 →𝑓=− 𝑑 𝑓𝑎𝑟
"𝐷𝑖𝑜𝑝𝑡𝑒𝑟"= 1 𝑓 = 1 − 𝑑 𝑓𝑎𝑟

23. Activity 7 (not graded)– A brief discourse about prescription eye glasses, computer glasses just FYI (if time is tight, skip to Activity 8)

24. Activity 8: Astigmatism
Astigmatism is a condition in which the lens is deformed such that it has elements of a cylindrical lens causing non-isotropic sharpness on the retina.
Simulate astigmatism by adding a cylindrical lens.
Correct for the astigmatism by fitting special “glasses” to correct for this condition. Note how the relative orientation of the cylindrical axes matter.
-128mm lens in slot “A”
+62mm lens in “Septum” slot

25. Activity 8: Astigmatism
First look at the image formed on the retina of a picture like this (draw one on a piece of paper).
Observe sharpness of the image of the various lines on the retina.
Place corrective lens in slots in front of the “cornea”
Observe corrected image on the retina.