3D Printed Schematic Model for Extraocular Muscles teaching
Authors: Salinas‐Alvarez Yolanda , Garza‐Gutiérrez Antonio , Quiroga‐Garza Alejandro , Elizondo‐Omaña Rodrigo E. , Gutierrez‐De‐La‐O Jorge , Guzman‐Lopez Santos 
Published: May 2022

There are many difficulties a student or educator can present in the anatomy course. Technological advances and availability of new tools have provided alternatives to improve the learning method.

A 3D model of an orbit and ocular globe (OG) was designed and 3D printed. It consisted of a roof, floor, medial and lateral walls, and a posterior wall. The superior and inferior orbital fissures were represented, as well as the common tendinous ring (Zinn's) and the optic canal from which a cylindrical axis extends in a 45° angle, representing the optic nerve (ON). At the end of this axis, a sphere an enarthrosis sphere simulates the OG. The medial wall is parallel to the OG’s axis, while the lateral wall is almost parallel to the ON’s axis. The OG was formed with polygons to allow better perception of the movements. The center of the sphere attached to the ON matches the center of the OG, resulting in the OG rotating without moving within the orbit.

Six holes were made in the OG, in which elastic threads were placed. In the anterior half of the OG, a hole for the superior, inferior, medial and lateral surfaces was made, corresponding to the insertions of the superior rectus (SR), inferior rectus (IR), medial rectus (MR), and lateral recti muscles (LR) respectively. On the lateral surface of the posterior half of the OG, a hole in the superior region was made for the insertion of the superior oblique (SO) and another in the inferior region for the insertion of the inferior oblique (IO). The four rectus muscles originate from the annulus of Zinn, and represented with holes that cross the posterior wall of the orbit in the common tendinous ring at the four points of insertion.

In the medial wall of the orbit, at the superior anterior corner, a trochlea was made, through which the thread representing the SO passes and is anchored to the posterior wall through a hole that is superior to the hole for the SR. On the same wall, but in the interior anterior corner of the orbit, we designed a hole to anchor the thread that represents the IO. The angles between the axes of the oblique muscles, recti muscles, and the axis of the OG were kept as close to reality as possible. In the model, the axis between the recti muscles and the OG’s is 20° (human orbit is 23°) and between the oblique muscles and the OG’s is 70° (human orbit is 51°).

The design allows an internal rotation when tightening the threads that are inserted in the superior half of the OG (SR, SO); if the inferior half are tightened (IR, IO), it causes an external rotation; if the recti are tightened, adduction occurs (except for the LR); if those representing the obliques and the LR are tightened, an abduction occurs; if those inserted in the anterior half of the OG (SR, IR, MR, LR) are tightened, the movement corresponding to its name is produced, and if those inserted in the posterior half are tightened, the movement occurs opposite to what their names indicate (SO, IO).

The model is effective and makes learning easier. Student perception has not been surveyed yet. Future version may improve the angle between the oblique’s and the OG’s axis. Pathological finding can also be exemplified.