# Please, ideas for a physiology model

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#### J.opt

##### Full Member
7+ Year Member
15+ Year Member

Hey, my physiology professor is letting us build a homemade model about a process o system having to do with physiology for extra credit, and I thought that it would be great if I did something that had to do with vision. I was looking into building a model like the one described by rpames here http://forums.studentdoctor.net/showthread.php?s=&threadid=71516&goto=nextoldest but my professor doesn?t want us to use lasers.
Do you guys have any ideas?

#### J.opt

##### Full Member
7+ Year Member
15+ Year Member
Anyone?
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#### Andrew_Doan

##### Doc, Author, Entrepreneur
Moderator Emeritus
15+ Year Member
How about building a model to demonstrate how the globe is made of concentric circles and then show how blunt trauma causes rupture of these circles when the eye expands with trauma.

You can use a balloon for the globe and use styrofoam strips to represent the corneal limbus, sclera, and other structures of the eye.

If you could use a laser pointer, then you could build a model to explain Snell's law and the critical angle of reflection. This is the principal behind why we can't see the trabecular meshwork without a gonioscopy lens.

sin(-1) i = (1.00/1.33) sin 90

critical angle = i = 48.75 degrees

where i = incidence angle of light (coming from water = tear film)
90 degrees = reflected angle of light (leaving from water to air)
1.00 = index of refraction of air
1.33 = index of refraction of water/tear film

Any light hitting the water-air interface less than 48.75 degrees will become internally reflected.

#### J.opt

##### Full Member
7+ Year Member
15+ Year Member
Thanks Andrew
I was thinking of using some strings to demonstrate how the sphincter muscle contracts and relaxes, but I think that I?m going to go with your fist idea.

#### Andrew_Doan

##### Doc, Author, Entrepreneur
Moderator Emeritus