|Year : 2020 | Volume
| Issue : 2 | Page : 209-212
Department of Ophthalmology, Government Medical College, Kozhikode, Kerala, India
|Date of Submission||16-May-2020|
|Date of Acceptance||17-May-2020|
|Date of Web Publication||25-Aug-2020|
Dr. I Karthiga
The Kerala State Housing Board, Working Womens Hostel, Chevayur, Kozhikode - 673 017, Kerala
Source of Support: None, Conflict of Interest: None
Extraocular muscles facilitate the eye movements. Examination of extraocular movements helps in the diagnosis of different local and systemic conditions. It also helps in differentiating congenital and acquired lesions.
Keywords: Extraocular movements, extraocular muscles, forced duction test
|How to cite this article:|
Karthiga I. Extraocular movements. Kerala J Ophthalmol 2020;32:209-12
| Introduction|| |
The muscles of the eyes are designed to stabilize and move the eyes. All eye muscles have a resting muscle tone that is designed to stabilize eye position.
| Anatomy|| |
Six extraocular muscles facilitate eye movements. Actions of these muscles depend on the position of the eye at the time of contraction.
4 Recti 2 Obliques
Vertical: Superior rectus Superior oblique
Inferior rectus Inferior oblique
Horizontal: Medial rectus
Four recti muscles originate at the orbital apex, the annulus of Zinn, and course anteriorly to insert on the anterior aspect of the globe at a varying distance from the limbus [Figure 1].
These insertions form the spiral of tillaux [Figure 2].
Recti is attached to sclera anterior to the equator.
The contraction of recti muscles pulls the globe backward and nasally.
Superior oblique arises from the apex of the orbit, runs forward to the trochlea, changes its direction and runs over the globe under superior rectus above and lateral to the posterior pole.
Inferior oblique arises anteriorly from the orbital walls near the lacrimal fossa, passes backward and laterally to insert in the posterior lower temporal quadrant of the globe.
Obliques are inserted on sclera posterior to the equator.
The contraction of oblique muscles pulls the globe forward and nasally.
| Range of Movements|| |
All movements of the globe can be analyzed in terms of coordinate system with three axes perpendicular to each other and intersecting at the center of rotation.
Z-axis is oriented vertically to coordinate horizontal movements. Similarly, X-axis oriented horizontally for vertical movements, Y-axis oriented obliquely for torsional movements [Figure 3].
| Categories of the Eye Movements to Be Tested|| |
- Ductions (one is open and other covered)
- Versions (both eyes open, fixing a target and moving in the same direction)
- Vergences (both eyes open, fixing a target and moving in the opposite direction)
- Saccadic movements (quick fixation movements)
- Pursuit movements (slow following movements).
| Precautions While Testing Extra Ocular Movements (Eom)|| |
- The patient head must be kept straight
- The target must be easy to see and small enough to ensure accurate fixation on it
- The target should be held about 40 cm from the patient's eyes
- Both eyes must be visible to the examiner
- Target should be moved smoothly at a moderate speed. It must be moved to the limits of gaze.
| How to Test Eom|| |
- Ductions: They are monocular eye rotations. One of the patient's eyes is covered, and with the other eye, asked to follow a visual target slowly through the cardinal positions of gaze [Figure 4]
- Horizontal ductions
- Adduction – Eye turns nasally
- Abduction – Eye turns temporally.
- Vertical ductions
- Deorsumduction or depression – Eye moves down
- Sursumduction or elevation – Eye moves up.
- Torsional movements
- Incycloduction or intorsion – Nasally directed tilting of 12'O clock meridian
- Excycloduction or extorsion – Temporally directed tilting of 12'O clock meridian
- They are binocular, simultaneous, and conjugate movements. The patient is asked to follow a target through the cardinal positions of gaze while viewing it with both eyes [Figure 5].
Muscles involved in each gaze are called yoke muscles or agonists. They are:
- Dextroversion (right-sided binocular horizontal movements) – Right lateral rectus and left medial rectus
- Laevoversion (left-sided binocular horizontal movements) – Left lateral rectus and right medial rectus
- Dextroelevation (right and up) – Right superior rectus and left inferior oblique
- Laevoelevation (left and up)) – Left superior rectus and right inferior oblique
- Dextrodepression (right and down)) – Right inferior rectus and left superior oblique
- Laevodepression (left and down)) – Left inferior rectus and right superior oblique
- Vergences: They are binocular, simultaneous, and disjugate movements
- Convergence – Simultaneous inward movement
- Divergence – Simultaneous outward movement.
- Saccadic: They are fast dart-like primitive movements. They are the first eye movements occurring 1–2 weeks after birth. They are not controlled by visual feedback as there is foveal suppression. It needs good muscle function
- Smooth pursuit: Slow accurate movements used to fixate and follow a target. It develops at around 2–3 months of age. They require foveal fixation and visual feedback to keep the eyes on the target.
| Grading of Eom|| |
The underaction is indicated by −1, −2, −3, and overaction as +1, +2, +3 for each extraocular muscle. This grading is on a scale of 7. If a scale of 9 is chosen an additional degree −4 and +4 for both underaction and overaction is added.
| Grading of Inferior Oblique Overaction|| |
Observe the angle the adducting eye makes with the horizontal line as it elevates and abducts.
- Grade 1+: upto 15° angle with the horizontal line
- Grade 2+: upto 30° angle with the horizontal line
- Grade 3+: upto 60° angle with the horizontal line
- Grade 4+: upto 90° angle with the horizontal line.
The overaction of the obliques can also be indirectly assessed in the following manner.
- Mild: If the vertical deviation (hypertropia for inferior oblique) is appreciable only in the direction of action of the muscle
- Moderate: Hypertropia on adduction itself
- Severe: Hypertropia is seen in the primary position itself.
For example: Right inferior oblique overaction:
- Severe – Right hypertropia in the primary position itself
- Moderate – Right hypertropia in laevoversion
- Mild – Right hypertropia in laevoelevation.
| Significance of Eom|| |
- To detect motility defects so as to localize the lesion
- To differentiate paralytic and restrictive defects
- A paresis missed on duction can be picked up in a version
- To differentiate supranuclear lesion from nuclear and fascicular lesions.
| How to Differentiate Lesions at Different Levels|| |
The ocular motor system is divided according to anatomic location into supranuclear, nuclear, internuclear, and infranuclear components.
It is important to distinguish supranuclear and internuclear from nuclear and infranuclear disturbances, because of the highly varied causes and different clinical pictures.
| Supranuclear Lesions|| |
- Affect both eyes (conjugate limitation)
- It does not produce diplopia
- Doll's eye phenomenon and Bell's phenomenon remain intact.
[Table 1] – Ocular motility disturbance and its site of lesion tests to be evaluated with EOM:
- Forced duction test (FDT)
- Forced generation test
- Differential tonometry.
| Forced Duction Test and Forced Generation Test-Procedure and Significance|| |
After anesthetizing the eye with topical 1% proparacaine drops, the patient lies in the supine position. The lids are retracted with the speculum.
The patient is asked to look in the direction of action of the muscle being tested (this relaxes the antagonist).
The eye is held at the limbus with fixation forceps or Pierse – Hoskin's forceps without pushing the globe posteriorly and rotated in the direction of action of the muscle.
If this movement is allowed freely, the FDT is said to be negative, i.e., paralytic.
If it is restricted, it is known as FDT positive, i.e., restrictive.
A posterior push towards the orbit slackens the recti muscles, and produce a false-negative FDT.
While testing oblique muscles, a posterior push is desired to exaggerate the tautness of obliques.
Another useful test to determine and quantify the ability of the muscle to contract is the active force generation test.
This is very useful to distinguish a restrictive squint from a paralytic squint in which secondary restriction has developed.
After holding the globe with a fixation forceps, the participant is asked to look in the direction in the field of action of the muscle being tested.
If there is a normal 'tug' felt, it indicates the muscle is normal but incapable of a movement because of the restrictive element.
If the 'tug' is weak, it indicates a paretic muscle which also has a restriction of its antagonist.
| Documentation of Eom|| |
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Wright WK. Pediatric Ophthalmology and Strabismus.3rd
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Sihota R, Tandon R. Parsons' Diseases of the Eye. 22nd
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Bowling B, Kanski J. Kanski's Clinical Ophthalmology. 8th
ed. USA: Elseiver; 2016.p. 731-2.
Sharma P. Strabismus simplified.2nd
ed. NewDelhi: CBS Publishers; 2013. p. 2-3, 6, 81-82, 10, 138, 129.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]