||Andrew G. Lee, MD, Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, TX; Professor of Ophthalmology, Weill Cornell Medicine; Daniel Bailey, Baylor College of Medicine Class of 2021
||Okay, we were asked to talk about Listing and both the Listing's plane and the Listing's law. So, as you know, your eyeball does not have infinite ways that it can move, and so the axes of rotation are analogous to an airplane. So, when an airplane flies, the airplane can move in the pitch plane, it can move in the yaw plane, and it has the roll plane. So, an airplane has three degrees of freedom. The three degrees of freedom are in the x, the y, and the z planes. The x, the y, and the z planes in an airplane are pitch, roll, and yaw. So, it's not like a car; an airplane can go up and down, side to side, and can roll. Your eyeball also does not have infinite degrees of freedom; it can only move in the pitch, the yaw, and the roll plane. And so, when we have movements, they have to fall within the Listing's plane. Orthogonal movements relative to the Listing's plane mean that we can move the eye from the primary position to any other position as long as we are confined within the rotational degrees of freedom of the pitch, the yaw, and the roll plane. And what that means for us in terms of Listing's laws: we cannot make our eyes just do any movement and we can't make them do different movements in different planes. They have to stay within the parameters defined by the Listing's law and the Listing's plane. So, in practical terms, what it means is we can only have hypertropia, esotropia, and exotropia. We can only have incyclotorsion or excyclotorsion. So, when we're defining the movements-eye movements-we have to know which plane we are moving in (x, y or z), what is the change in the rotational freedom that we have, and-relative to the Listing's plane-what movement has occurred relative to the Listing's plane, which is the center, here, of the eye. And that's really great if you're an airplane, but a spaceship would be better if we could move our eyes independent of the three axes that we have been confined. And so, Listing's idea applies to strabismus and strabismus surgery. And understanding the Listing's plane and the Listing's law helps us understand how the eye movements occur and what the limitations on those eye movements are.