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!


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 Skull Structure
Explaining the skull structure between horses and humans, and how this affects
the cardinal directions.
Eye Muscles
It helps to understand the ocular anatomy if you’re going to understand cardinal
directions of eye movement.
There are several ways to document large eye deviations. This is my preferred method for large angle ductions.
EOM documentation
This is another method to document eye tropias. On this scale, “0”
is normal, while “-4” is no movement.
Cover Uncover Test
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.
Dr. Timothy Root is a practicing ophthalmologist and cataract surgeon in Daytona Beach, Florida. His books, video lectures, and training resources can be found at:


  1. Dr.root a salute to u.wat an amazing job you have done.sir please continue to do this noble work by giving out these great informative and intereting lectures.thank you.hope to meet you some time in the future.thank you again

  2. Hi Dr.Root
    In the frist I want say thank you for your lectures
    I have a question when we do the glasses to the patient we but prism in front of the natural eye or in front of the eye in which have tropia
    Thank you

  3. Dr.Root
    I learnt retinoscopy prety well with the help of your video and now the difference between Tropias and Phorias. Your explanations are simply simple. Thank you so much.
    Sir, I wish to see a animated/live demo of usage of JCC (Jackson’s cross cylinder).
    Thanking you once again.

  4. 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.

  5. @ 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

  6. Thank you!! I am a medical student and i now can totally understand tropis and phoria. hope i can make a Mandarin version in the future. Love your work~~!!

  7. 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.

  8. thank you so much DR ROOT &thanks GOD you are there for me am so greatful for your effort to make ophthalmology easier for us.

  9. thank you for the care and Great work Doc we appreaciate your concern keep Posting them

  10. I have just returned to COA after 15 years away. Your videos have been a lifesaver!!! Thanks so much for posting these, I’ve watched every single one!

  11. I’m a optometies in china,I love your thinking,it help me know something more easy.I try to translate your lectur. I think it will be very helpful.I hope that you can give me some advice。

  12. Thanks for giving us such an difficult topic in a simple and easy way, otherwise it was not clarified to me since last two years in ophthalmic classes


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