3 & 4. Extraocular Muscles And Ocular Motility Flashcards
Explain the point centre of rotation in the eyeball?
This is the centre most point and all eyeball movements occur at this point.
What is centre of rotation in an eyeball?
Point that lies on the plane of equator.
Describe the 3 axes that the eye rotates around?
- Z-axis: Horizontal rotation
- Y-axis/ optical axis: cyclorotation
- X-axis: vertical rotation
What are the 3 axes of the eye called?
Axes of Fick
3 axes and centre of rotation lies on which plane?
Listings plane- imaginary plane
Define Donder’s Law
That the orientation of the eye is always the same when the eye is aimed in a particular direction.
For horizontal and vertical movements, is cyclo rotation involoved?
No
Cyclo rotation only happens when looking where?
When looking at diagonal directions
Define listings law
Each movement of the eye from the primary position to any other position involves rotation around a single axis lying in the equatorial plane called listing’s plane.
What are the 3 monocular eye movements (Ductions)
- Lateral : Abduction- outwards, adduction- inwards
- Vertical: Depression- downwards, Elevation- upwards
- Rotational: Excycloduction- rotate outwards, Incycloduction- rotate inwards
Lateral rectus is operated by? And this rectus rotates around which axis?
Operated by: 6th abducens nerve
Rotates around: z (vertical axis)
Lateral rectus in primary position causes what action?
Abduction only
Lateral rectus in secondary position causes what action?
In elevation: some elevation
In depression: some depression
Medial rectus is operated by? And this rectus rotates around which axis?
3rd oculomotor nerve
Rotates around z axis
Medial rectus in primary position causes what action?
Adduction
Medial rectus in secondary position causes what action?
In elevation: some elevation
In depression: some depression
Superior rectus is operated by? And this rectus rotates around which axis?
3rd oculomotor nerve and rotates arround the z-axis
Superior rectus in primary position causes what action?
1: Elevation
2: Incycloduction
3. Adduction
Superior rectus in secondary position causes what action?
At 23 degrees: abduction: more elevation
At 67 degrees: adduction: more incycloduction
Inferior rectus is operated by? And this rectus rotates around which axis?
3rd oculomotor nerve, rotates around x-y plane, 67 degrees nasal to y.
Inferior rectus in primary position causes what action?
1: Depression
2: Excycloduction
3: Adduction
Inferior rectus in secondary position causes what action?
At 23 degrees: abduction: more depression
At 67 degrees: adduction: more excycloduction
Superior oblique is operated by? And this rectus rotates around which axis?
4th (trochlear) nerve, rotates around x-y plane. 39 degrees temporal to y
Superior Oblique in primary position causes what action?
1: Incycloduction
2: depression
3: abduction
Superior Oblique in secondary position causes what action?
At 51 degrees: adduction: more depression
At 39 degrees: abduction: more abduction
Inferior oblique is operated by? And this rectus rotates around which axis?
3rd (oculomotor) nerve, rotates around x- y plane, 39 degrees temporal to y
Inferior Oblique in primary position causes what action?
1: Excycloduction
2: Elevation
3: Abduction
Inferior Oblique in secondary position causes what action?
At 51 degrees: adduction- more elevation
At 39 degrees: abduction- more abduction
What is RADSIN?
Recti adduct (Superior and Inferior rectus)
Describe what is vergence and versions
Vergence: movement of eyes in opposite directions, disjunctive
Versions: movement of eyes in the same direction, conjugate.
Define ipsilateral antagonists, give an example
Pull one eye in opposite direction (when one muscle is relaxed and the other muscle is contracted). These muscles are found in pairs in the same eye.
Example: Right lateral contracts and right medial relaxes- when right eye looks to the right
Define contralateral antagonists, give an example
When muscles are relaxed they move eyes in the same directions. Also known as yoke muscles.
Example: When looking to the right: Right and left medial muscle is relaxed
What is sherrington’s law of reciprocal intervention, give an example
Increased innervation to a muscle is accompanied by a decrease in innervation in the ipsilateral antagonist.
Example: RLR contracts, RMR relaxes- when looking to your right
What is herings law?
When innervation to a muscle changes, an equal change in innervation occurs in the contralateral synergist (innervation to right lateral rectus will result in equal innervation to the left medial rectus).
Sherrington’s law of reciprocal intervention and herings law all to binocular movements in which direction?
In ALL directions: Horizontal, vertical or diagonal versions and vergences
The function of how many EOMs in each eye is tested?
6
What is primary position?
When eyes are looking straight ahead
We need to examine how many positions of gaze?
9
What is secondary position?
Eyes straight up/ down/ right/ left
What is tertiary position?
Eyes up and right/ up and left/ down and right/ down and left.
Describe the difference between Comitant and Incomitant
Comitant: deviation is manifest during testing an the deviation is the same in all directions. Incomitant: Deviation is manifest during test and deviation varies in different position of gaze.
4 causes of incomtancy (congenital-4 and accquired-3)
Congenital: neurogenic, mechanical, myogenic, form (under development of nerve/ nucleus, birth trauma).
Acquired: Neurogenic, mechanical and myogenic.
Hirschberg, krimsky and bruckers tests is sometimes referred to as?
Corneal Reflection (Reflex) tests
What is anisometropia
Two eyes have different refractive powers
Purpose of corneal reflection test
- Objective means of assessing ocular alignment
- Objective evaluation of anisometropia (bruckner)
On what kind of patients is corneal reflection test performed?
It can be performed on all patients but most importantly used on patients who can’t cooperate with other tests e.g, babies
How is Hirschberg test performed?
*Sit F2F with patient, straight ahead, same eye height
* Pen torch held so patient looking in primary position
(straight ahead, not up/down/left/right)
* Typically within arm’s length (so you can use prisms)
* If patient not automatically looking at light either make a noise or flash pen torch to get attention
* Observe corneal light reflections
What are you looking at in Hirschberg test
If eyes are straight: Symmetrical Reflex; this test is used to find is patients have a tropia.
Why does angle of Kappa exist
The visual axis doesn’t necessarily line up with the pupillary axis.
What is positive angle Kappa?
When the corneal light reflex is nasal to the centre of the pupil
Corneal diameter varies with?
Age
Adult corneal diameter is?
11-13mm
Corneal diameter from birth to 1 year old is?
9.5-11.5mm
Each 1mm displacement for corneal reflex position is how many degrees?
7
Variation in angle kappa could be due to?
- Space between eyes
- Rx
What kind of symmetry is seen in patients with a phoria?
Symmetric reflections
When is Krimsky Test done?
After Hirschberg
Why is Hirschberg test done?
IF misalignments observed in Krimsky test, this test is done to measure the prism needed by the patient.
How is Hirschberg test done?
Add prism in front of fixing eye- watch strabismic eye, increase prism until reflex in strabismic eye matches original symmetrical position of fixing eye.
Describe the role of medial and lateral rectus? - in terms of eye movement
Medial Rectus: Move the eye inwards
Lateral Rectus: Move the eye outwards
Ocular motility testing is used to assess?
Eye movements
On the listings plane, y-axis is also known as?
Optical axis
Monocular eye movements are called?
Ductions
What is primary position?
When head is looking and eyes are looking straight
Only the inferior rectus and inferior oblique?
Extort- turn the eyes out.
Only superior rectus and superior oblique?
Intort: Turn the eyes in
What is meant by EOM?
Extra ocular muscles
Purpose of ocular motility?
This is an assessment of eye movements
Monocular eye movements are known as?
Ductions
What are the 3 types of ductions possible?
- Lateral
- Vertical
- Rotational
What is primary position?
When head and eyes are looking straight ahead
Why do some muscles have more then 1 action when they contract and other muscles don’t?
Horizontal, lateral and medial rectus muscles only have 1 action when they contract, because they lie along one of the rotation axes, other muscles don’t (other muscles lie oblique) hence they have more then 1 action.
Identify the difference between Incyclovergence and Excyclovergence vs Dextrocycloversion and Levocycloversion
Incyclovergence: Both eyes turning in (eyes moving in opposite directions)
Excyclovergence: Both eyes turning out (eyes moving in opposite directions)
Dextrocycloversion: Both eyes moving in the same direction to the right
Levocycloversion: Both eyes moving in the same direction to the left
What is meant by secondary position?
Eyes are looking straight up/ down/ right/ left
Purpose of corneal reflection tests?
Objective means to assess ocular alignment and bruckers test is an objective evaluation of anisometropia
What is the point of reference used to identify symmetry when doing the Hirschberg test?
The centre of the nose is used as a reference point
Role/ function where bruckners test is most useful
In children to identify if they have anisometropia
How is bruckners test performed?
Use ophthalmoscope at 0D. Sit far away from patient such that both eyes can be seen through the ophthalmoscope. Look at the red reflex reelection seen. This test is used to identify asymmetry between pupils and anisometropia.
In bruckners test if asymmetry seen in corneal reflex this implies?
Strabismus
In bruckners test if difference in brightness of fundus is observed, it is suggested?
Difference in refraction in both eyes
In bruckners test if fundus reflex is elliptical, what does this suggest ?
Significant astigmatism
In patients with black or white pupils seen in bruckner’s test, what does this suggest?
Black patches: could indicate cataract
White pupils: Retinoblastoma - in a young child. This needs urgent referral.
What is the purpose of ocular motility test?
To assess ocular movements
How is ocular motility testing done?
- Patients glasses off
- Sit at the same eye level with patient
- Patient to look straight ahead, observe for any AHP, if present correct it
- Pen torch, 50cm away
- Move light to 8 positions of gaze (3 secs out, 3 secs back).
What observations are taken by asking patients questions, and how are these corrected?
- Ask patient if they can see 1 or 2 spots of light
- Ask patient if they are experiencing any pain or discomfort
- If vision gone double: can you make it single again?
- Are images side-by-side, or on top of each other?
If a problem is identified in a position of gaze, what is done? - during ocular motility testing
Perform cover test in that position of gaze
What is the next step if you identify that a patient has a strabismus only when they have the glasses off?
Assess if the deviation is comitant
How does anisometropia affect test results?
One eye will accommodate more then the other eye as you switch between the 2 eyes.
What is the impact on patients with a phoria seen while performing ocular motility test?
Patients may experience double vision, in extreme ends of gaze in almost all directions.
What is an AV pattern?
Describe the A and V patterns
An increases or decrease in deviation as patients look in different direction of gazes.
A pattern: Patients have less deviation when they look up compared to when they look down.
V pattern: Patients have greater deviation when they look up compared to when they look down.
Describe how prism cover test is performed
- Patient will hold fixation target at arms length.
- Place best estimated prism in front of the eye and repeat cover test till no movement is seen.
- Record results with size of deviation.
Aim of performing prism cover test
Measure size of deviation
How is the correct side of prism identified?
Image moves towards the apex
How is base direction of prism identified?
Base goes in opposite direction to the movement of the eye.
Eye turned out: Base in
Double maddox rod is a test for?
Cyclo deviation
Are cyclo deviations symptomatic?
What muscles does this deviation affect?
Congenital are rarely symptomatic
Acquired are symptomatic
It generally affects oblique muscles could also be SR/ IR
What happens to patients eyes and images in Excyclo-deviation and Incyclo-deviation
Excyclo-deviation: eyes turned out and image rotated inwards.
Incyclo-deviation: eyes tuned in and image rotated inwards.
How is double maddox rod done?
- Spot light on
- Place 2 vertical maddox rods in patients trial frame: ideal if both different coloured.
If no cyclo deviation: both lines are straight
If cyclo deviation: lines tilted
How to record patients with cyclo- deviation identified with maddox rod?
If patients sees tilted lines, turn the maddox rod in the frame until both lines are aligned, read and record the axis off from the trial frame.
How to record patients with cyclo- deviation identified with maddox rod?
If patients sees tilted lines, turn the maddox rod in the frame until both lines are aligned, read and record the axis off from the trial frame.
Optic nerve does not run straight through the orbit it is slightly curved, what is the benefit of this?
Allows eye movements
Ocular motility tests?
Assessment of eye movements
Muscles that move the eyes outwards are called?
Lateral rectus
