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I ANATOMY            

II PHYSIOLOGY                 

IV FIXATION INSTABILITY  

V SUPRANUCLEAR to NUCLEAR   

VI VESTIBULAR SYSTEM  

 VII CEREBELLAR EYE   MOVEMENTS 

VIII VISUAL FIELDS, PUPIL & THE EYE

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Video 1. Introduction:Oculomotor and Vestibular Systems

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Video 2. Performing a Standard Eye Examination: Professor M Strupp, University of Munich
This video covers the following topics:

(vv)PerformingStandardEyeExamination.mp4(tt)

 

 

Video 3. Systematic Examination of Eye Movement. Professor A Moodley, NASA Registrar Weekend, 2019

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Primary eye movements can be divided into those that produce gaze shifts which bring an object of interest onto the fovea, and those that promote gaze stabilisation. 

Distinct oculomotor mechanisms provide for the achievement of foveation across a variety of visual circumstances.  The fovea is the portion of the retina with the highest visual acuity, hence maintaining image focus upon this structure promotes image processing and visual fixation.  The various types of eye movements serve to keep the visual target on the fovea stable and thus avoid illusory movements (oscillopsia) and blurred vision under a variety of visual conditions which include:

Symptoms

Patients with ocular motor disturbances usually report the following symptoms in isolation or in combination1:

Video 4.Normal eye movement evaluation, including checking smooth pursuit and saccades, both vertical and horizontal

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Normal Eye Movements

The six physiological forms of eye movement are1:

INFORMATION GATHERING:

1. Saccades are fast eye movements that mediate rapid shifts of gaze to a new fixation target.  

2. Smooth pursuit eye movements allow foveation while tracking a slowly moving target.

3. Vergence movements represent an evolutionary adaptation for frontal vision with binocularity.  Vergence movements involve eye movements in opposite directions for simultaneous foveation.

4. Gaze holding is the ability to keep the eyes in an eccentric position.

REFLEXIVE/STABILISING:

5. Visual fixation During head movements, visual fixation upon still objects is achieved through the recruitment of vestibular mechanisms that correspondingly move the eyes in an equal and opposite direction in order to maintain foveation. This is achieved through the vestibulo–ocular reflex (VOR); the signal triggering eye movements comes from the labyrinth, which keeps the image of the visual surroundings stable on the retina during head movements

6. With sustained head rotation or environmental movement with the head steady, optokinetic nystagmus, which combines slow pursuit eye movements punctuated by saccadic refixations, promotes the re-establishment of image focus. This is essentially a reflex which is triggered by moving visual targets.

 

Examination of Eye Movements2  

Ocular motility examination should include bedside evaluation and laboratory recording of1:

1.  Ocular Misalignment confirmed with a cover test in primary gaze, during both near and distant fixation. 

2. Range of eye motion and gaze holding function :10–400 for horizontal gaze, and 10–20for vertical gaze.
    Note that a moderate restriction of upward gaze is common in elderly individuals

3. Involuntary eye movements: nystagmus or inappropriate saccades 

4. Saccades both horizontal and vertical, should be assessed for latency, velocity, accuracy, and conjugacy.

5. Smooth Pursuit (SP) may be evaluated by asking the patient to track a small target moving slowly in the horizontal or vertical direction with the head still.  If the pursuit movement does not match the target velocity, corrective catch-up or back-up saccades would occur. Since many neural structures are involved in generation of SP, and various factors, impaired pursuit general ly does not have a localizing value.

6. Vestibulo-ocular reflex (VOR):  may be evaluated bedside using head impulse tests (HIT), visual enhancement of the VOR, and visual cancellation of the VOR.

7. Optokinetic Nystagmus (OKN):  induction of OKN may be useful in some patients who have difficulty initiating voluntary saccades.

8. Vergence Eye Movements:  tested by having the patients look back and forth between a distant and a near target.

9. Tests of peripheral vestibular function: 

10. Inspection of head/body posture 

References

  1. Strupp M, Kremmyda O, Adamczyk C, et al. Central ocular motor disorders, including gaze palsy and nystagmus. J Neurol. 2014;261 Suppl 2:S542-58
  2. Frohman EM, Solomon D, Zee DS. Vestibular Dysfunction and Nystagmus in Multiple Sclerosis. Int MSJ 1995 3(3):87-99.