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!
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.
Explaining the skull structure between horses and humans, and how this affects
the cardinal directions.
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.
This is another method to document eye tropias. On this scale, "0"
is normal, while "-4" is no movement.
The cover-uncover test is used to pick up small-angle tropias.
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.
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.
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!
