Ocular Kinematics and Muscle Anatomy Flashcards
What is the branch of classical mechanics that describes the motion of points, bodies, and systems of bodies, without consideration of the forces that cause it
kinematics
What does kinematics focus on and exclude?
Focuses on motion, excludes forces
Describe the CN innervation of the 6 EOMS
CN 3 Innervations the superior, inferior, and medial rectus in addition to the inferior oblique; the superior oblique is innervated by CN 4; the lateral rectus is innervated by CN 6
The ____ is not a contractile tissue, but force direction comes from the muscle
superior oblique tendon
Where does the muscle attach to the bony orbit?
origin
Where does the muscle attach to the globe?
insertion
What forms the muscle cone?
The recti muscles, Origin at Annulus of Zinn
What goes thru the SOF and above the Annulus of Zinn?
lacrimal, frontal, trochlear, superior ophthalmic vein
What goes thru the SOF and Annulus of Zinn?
nasociliary, oculomoter superior and inferior, and abducens
What goes thru the optic canal?
optic nerve and ophthalmic artery
What goes thru the IOF?
zygomatic, infraorbital nerve artery and vein, and the inferior ophthalmic vein
What is optic neuritis and what are the signs?
inflammation of the optic nerve; pain on EOMS is a sign, if retrobulbar there is APD
Superior Rectus: innervation, origin, insertion, and fun fact
CN 3; superior annulus of zinn; 23 degree angle w/ primary gaze on superior sclera, 7.4 mm from limbus (furthest); connected sheath w/ levator= coordinated eye movements with eyelids
Superior rectus actions:
elevation, adduction, and intorsion
Inferior Rectus: innervation, origin, insertion, and fun fact
CN 3; inferior annulus of zinn, 23 degree angle w/primary gaze on inferior sclera (6.7 mm from limbus); IR passes of IO and fascia below both contributes to lockwoods ligament
Inferior rectus actions
depression, adduction, extorsion
Lateral Rectus: innervation, origin, insertion, and fun fact
CN 6; upper and lower limb of annulus AND process of greater sphenoid wing; parallel to medial recuts 6.9 mm from limbus; fascial expansion from muscle sheath of lateral check ligament; whitnall’s tubercle has attachment at lateral wall of orbit
Lateral rectus action
abduction
Medial Rectus: innervation, origin, insertion, and fun fact
CN 3; upper and lower annulus AND optic nerve sheath; 5.5 mm from limbus (most anterior); medial check ligament fascial expansion from muscle sheath attaches to medial orbit
Medial rectus action
adduction
What is the spiral of tilleaux?
The nature of insertions of EOMS; medial is most anterior and superior is least anterior; most surgical correction done on medial rectus then lateral rectus
Superior Oblique: innervation, origin, insertion, and fun fact
CN 4; ANATOMICAL origin is lesser wing of sphenoid, PHYSIOLOGICAL origin is cartilaginous trochlea of the superior medial orbital wall (muscle ends before trochlea and tendon passes thru); insertion lateral posterior globe
Superior oblique actions
Intorsion, Abduction, Depression
Explain the three superior oblique vector forces:
primary gaze- straight ahead
adduction- 54 degrees medial
abduction- 36 degrees lateral
Inferior Oblique: innervation, origin, insertion, and fun fact
CN 3; originates in ANTERIOR ORBIT at maxillary bone inferior to the nasolacrimal fossa; inserts posterior-lateral globe, mostly inferior at 51 degree angle
Inferior oblique actions
Extorsion, abduction, elevation
What is the tangential point?
Where the center of the muscle or tendon first touches the globe; tangent indicates direction of pull; position changes when the muscle contracts or relaxes and the eye moves. THIS IS NOT THE INSERTION
What is the arc of contact?
The arc formed between the tangential point and the center of the insertion on the sclera; varies in lengths as the muscle contracts
What is the muscle plane?
Determined by a tangential point and the center of rotation; describes direction of pull of the muscle; determines the axis of rotation
Strabismus Sx ReSECTion
To remove a section of the medial of lateral rectus; shorter muscle=more pull
Strabismus Sx ReCESSion
To slide backwards; medial or lateral rectus is cut and sutured to the sclera more distally; muscle doesn’t reach as far=less pull
Strabismus Sx
Can use resection and recession in combination; results in new insertion, new arch and new tangential
Strab Sx Transposition
For vertical deviations; move lateral or medial rectus up or down on the globe; very small change in position
What is the field of fixation
An area within which central fixation is possible by moving ONLY the eyes aka the area the fovea can hit w/o moving your head
Explain the relationship between bino and mono fixation
In bino fixation, both foveas must be pointed at the same place at the same time, this area is actually smaller than monocular fixation
What differences are there in field of fixation?
Large individual differences, limits depending on eye structure and refraction of globe, age-dependent decreases from EOM restriction starting the the 60s
What is practical field of fixation?
The area central fixation is possible including head movements
What is primary gaze/position?
The reference point for ocular rotation, lines of sight are horizontal and perpendicular to the line between their centers of rotation
What is secondary position?
The position assumed when the eye moves from primary position along the horizontal or vertical axis
What is tertiary position?
The position assumed when the eye moves to any other location
What is a duction?
A rotation of a single eye; add, abd, supra, infra
What is a version?
A rotation of both eyes
What is a vergence?
Binocular eye movements in opposite directions; convergence and divergence
What is cyclotorsion?
Rotation (counter)clockwise- difficult to treat surgically and therapeutically; intorsion- 12 to nose; extorsion 12 to ear
