Definitions/EOMs Flashcards
Why is ocular movement assessed?
- Establish the extent of mov’t of the globe
- prove the integrity of the diff mov’t systems/nervous system pathways
Tangential Point
Point at which the center of the muscle or of its tendon first touches the globe
Muscle Plane
The tangent to the globe at the tangential point and the center of rotation
Axis of Rotation (AOR)
Perpendicular to the muscle plane erected in the center of rotation corresponds to each muscle plane
Arc of Contact
Arc formed b/t the tangential point and the center of insertion of the muscle on the sclera, the area where the muscle exerts its action
Angle Kappa
- Angle formed by intersection of the pupillary axis and visual axis
- Caused by failure of the optical and visual axes of the eye to coincide
Pupillary axis
Line passing through the center of the pupil perpendicular to the cornea
Optical axis
Line connecting the optical centers of the cornea and the lens
Visual axis
AKA line of sight, connects the fovea with the fixation point
Positive angle kappa
- Fovea lies temporal to the posterior pole and reflection = nasal
- Referred to as pseudo exotropia
- This is normal (avg = 5.082 degrees)
Negative angle kappa
This is unusual
Fovea lies nasal to the posterior pole and reflection is temporal
Referred to as pseudoesotropia
Angle alpha
Angle b/t the optical ax’s and the visual axis = nodal point/angle alpha
Angle gamma
Angle between the optical axis and fixation axis referred to the center of rotation
What is the only angle that can be clinically measured of the ones we discussed?
Angle kappa
Where does the optical axis (AB) touch the posterior pole?
Slightly nasal and inferior to the fovea
What are conjugate movements?
Movements of the eye in the same direction at the same time
What are versions?
Binocular rotations of the eyes in qualitatively the same direction (aka conjugate movements)
What is dextroversion?
Both eyes rotating about the z axis to the right
Levoversion
Both eyes rotating about the z axis to the left
Dextrocycloversion
Rotations about the y axis such that the upper portion of both eyes tilt to the patient’s right
Levocycloversion
Rotations about the y axis such that the upper portion of both eyes tilt to the patient’s left
Disconjugate
Movements of the two eyes in opposite directions to see objects singly at different distances from us aka vergences
Vergences
Aka disjunctive mov’ts; movement of the 2 eyes in opposite directions
Convergence
Eyes turn inward
Vergence
Eyes turn outward
What is true torsion?
Rotation of the eye about its anteroposterior axis
Fusion
Formation of one image from the two images seen simultaneously by the two eyes
Motor fusion
Adjustments made by the brain in innervation of extraocular muscles to bring both eyes into bifoveal and torsional alignment
How is motor fusion stimulated?
Disparity in images received fro, the two eyes such as fixation object moving towards or away from the subject
Sensory fusion
- Aka binocular vision, sensory fusion, stereopsis
- Integration in the visual sensory areas of the brain of images seen with the two eyes into one picture
- Position of eye is determined by the equilibrium achieved by the pull of all 6 EOMs
What is an example of sensory fusion and what stimulates it?
- The waterfall illusion
- Stimulus to sensory fusion is the excitation of the corresponding retinal images
Heterophoria
Latent deviation of the eyes which are held straight by binocular fusion
Heterotrophia
Manifest deviation of the eyes
Orthophoria
- A sense of any tendency of either eye to deviate when fusion is suspended
- this is rarely seen clinically (small phoria is normal)
Prism diopter
- Unit of angular measurement used to characterize ocular deviations
- 1 diopter prism reflects ray of light towards base of prism by 1 cm
- One degree of arc = 1.7 PD approx
Primary position of gaze
Head and eyes are both aligned w object of regard
Secondary position of gaze
- Posterior of the eyes when either a purely horizontal or purely vertical mov’t is made from primary position
- NO associated tilt of the vertical meridians with respect to objective vertical
Tertiary position
Position of the eyes when they move from primary position to any other position EXCEPT secondary position
False torsion
- The APPARENT cyclorotation of the eye associated with the change in direction of regard from primary position to some tertiary position
- It is NOT true torsion
Antagonist
The muscle that resists the pull of the agonist
It must relax for a new direction of gaze to be achieved
Have opposite field of action
Agonist
The muscle that contracts to pull eye in desired direction
Field of action
Direction of gaze in which the muscle exert its greatest contraction force as an agonist
Synergistic
Muscles that have the same field of action
Medial Rectus
Primary - adduction
Lateral rectus
Primary-abduction
Inferior rectus
Primary- Depression (greatest when abducted)
Secondary - Excycloduction (greatest when adducted)
Tertiary - Adduction
Superior rectus
Primary- Elevation (greatest when abducted)
Secondary - Incyclorotation (greatest when adducted)
Tertiary - Adduction
Inferior Oblique
Primary - Excycloduction (greatest when abducted)
Secondary - Elevation (greatest when adducted)
Tertiary - Abduction
Superior oblique
Primary - Incycloduction (greatest when abducted)
Secondary - Depression (greatest when adducted)
Tertiary - Abduction
Spiral of Tillaux
Insertions of the rectus muscles are not equidistant to corneal limbus they are inserted as a spiral
Listing’s plane
- Plane passing they the head and center of rotation of the eye perpendicular to the line of sight when eyes are in primary position
- x and z lie in this plane
Three axes of Fick
Mov’t of globe takes place around the three axes of Fick (x,y,z) all passing thru center of rotation
Listing’s Law
Mov’t of the eye from primary position to any other position is equivalent to a single rotation about an axis in Listing’s plane
Donder’s Law
Angle of tilt for a given tertiary position of the eye is always the same regardless off the path the eye has used to obtain that position
Sherrington’s Law of Reciprocal Innervation
When an agonist contracts during mov’t there is a simultaneous and equal relaxation of the antagonist
Herring’ s Law of Equal Innervation
Yoked muscles are equally innervated and innervation is based of the fixating eye
Yoke pair
- For mov’t of both eyes in the same directions, the corresponding agonist muscles wit the same FOA = yoke pair
- Pair of agonist muscles with same primary action
Why is there a difference between the fields of action and diagnostic positions of gaze?
Diagnostic positions of gaze are used to ISOLATE a specific muscle to check function
-based upon biomechanics of the eye
Ex.) when eye is fully abducted only IR can depress the eye
Concomitant
- Strabismic deviation is equal magnitude in all fields of gaze
- Deviation not affected by which eye is fixating or direction of gaze
- Typical in childhood/non-paretic strabismus
Incomitant
- Deviation varies according to which eye is fixating and the direction of gaze
- Typical in recent onset of EOM paresis/acquired strabismus
- Will cause overaction of the non-affected eye
Primary deviation
Incomitant deviation measured w normal eye fixating
Secondary deviation
Incomitant deviation measured with affected eye fixating
