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Tropias and Phorias (Video)

This video lecture covers ocular motility, specifically the difference between tropias and phorias. This is a simplified approach to detecting strabismus and documenting your findings. I’ve created an animatronic set of eyes out of cardboard to simulate these findings!

length: 17:23 minutes

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TropiaVsPhoria.m4v (139 MB)


Screen Captures and Notes

Tropia Definition:
Misalignment that is always there, even when both eyes are open and attempting
to work together. Large angle deviations are obvious. If small angle, you can
detect it with the Cover-Uncover test.

Phoria Definition:
Misalignment that only occurs some of the time, such as when the synchronization
between the eyes is broken by covering one eye. You can “break fusion” using
the Cross-Cover test.

Exotropia is when an eye turns outwards.

Esotropia is when an eye turns inwards.

Hypertropia is when an eye turns upwards.

Hypotropia is when the eyeball turns downwards.

horse eye
Explaining the skull structure between horses and humans, and how this affects
the cardinal directions.

Eye anatomy
It helps to understand the ocular anatomy if you’re going to understand cardinal
directions of eye movement.

cardinal directions
There are several ways to document large eye deviations. This is my preferred
method for large angle ductions.

cardinal eye muscles
This is another method to document eye tropias. On this scale, "0"
is normal, while "-4" is no movement.

Cover Uncover Testing
The cover-uncover test is used to pick up small-angle tropias.

Cross-Cover Test
The cross-cover test (also known as the alternate cover test) is used to tease
out phorias. This works because you break fusion between the eyes.



Wow! Great explanation and animations!

Comment by Tom — November 8, 2010

Great explanation

Comment by granny — December 18, 2010

Great explanation and we enjoyed your lecture! Thank You

Comment by Dr. P class at ACC Anaheim — February 11, 2011

it is more than great video.you simplified many obstacles.thank you very much.

Comment by siso — March 13, 2011

well i am just 14 years old and i dont get the explnation so lets hope next time

Comment by zach — April 17, 2011

Thank you very much for your nice videos

Comment by dr,zainab — August 7, 2011

thank you for you intrsting lecture but we need more lecture to cover all point about squint

Comment by elbarody — August 10, 2011

simplified the basics of squint.can u add some more lectures about squint.

Comment by sonykjose — August 17, 2011

thank you very much for your excellent video

Comment by benny — October 15, 2011

Wow great video! Thanks

Comment by Derek — January 24, 2012

I would like to point out that a you defined a tropia as a misalignment that is always there. A trope can be also be intermittent, and therefore not always there.

Comment by Aaron — February 16, 2012

@ Aaron:

Thanks for the feedback. I purposefully kept the definition of tropia as simple as possible. You are correct, in that you can also have an “intermittent tropia.” You can also have an alternating tropia, convergence-related tropia, and many other “types” of tropia/phoria depending upon how you like to name things.

When I put this presentation together, I felt it safer to avoid these nuances. I feared that discussing the intermittent nature of phorias/tropias would muddy the waters for the beginner and make the primary difference (between phoria and tropia) that much harder to grasp.

Thus, the definition I used is simplified … but still useful and valid for a beginner. Perhaps I’ll go into further detail in a future lecture. Thanks!

Tim Root

Comment by Tim Root — February 16, 2012

Hi Tim,

Great lecture, very easy to follow. however i am a little confused as to what you meant by a ‘right esophoria’ (mentioned towards the end of the lecture). Ive always understood phorias being a bilateral misalignment of the visual axis, however you could have an esophoria which breaks down to alternating esotrpia…then breaking down further to maybe a right esotropia as the eyes fatigued with time.

Comment by NB — August 20, 2012

thank u so mch sir ..ur lectures r so marvellous
.They should be a part of the curriculum..

Comment by Tulika Gupta — September 14, 2012

what are the yoke muscles involved in dextroelevation?? please give some explanation as well

Comment by kushal — July 30, 2013

its a very nice video& lecture that i appreciate………

Comment by tibebu kassie — November 19, 2013

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