Optokinetic System and Vestibular Function

Questions and Answers

What role does the optokinetic system play in relation to the vestibular system?

It completely replaces the vestibular system during motion.

It works independently without any influence from the vestibular system.

It functions only during rapid head movements.

It supplements the vestibular system during sustained rotations. (correct)

What induces movement in the endolymph of the horizontal semicircular canal?

Rapid movements of the upper body.

Movement of the eyes in response to a visual stimulus.

Caloric stimulation of the external auditory meatus. (correct)

A lateral head turn toward the left. (correct)

Which structure inhibits the ipsilateral abducens nucleus during the optokinetic response?

The vestibular nuclei. (correct)

The contralateral lateral rectus muscle.

The abducens nerve.

The medial longitudinal fasciculus.

What does the absence of slow and quick phases of eye movement indicate during the OKN test?

Potential dysfunction in eye movement control. Signup and view all the answers

What is the primary function of the abducens nucleus?

To innervate the lateral rectus muscle and facilitate eye movement. Signup and view all the answers

How is the optokinetic response provoked?

By a compelling full visual field stimulus. Signup and view all the answers

What is a bedside test that evaluates foveal pursuit and refixation saccades?

Pocket tape test. Signup and view all the answers

What is the role of the medial longitudinal fasciculus (MLF) in eye movement?

To connect cranial nerve nuclei responsible for eye movement. Signup and view all the answers

Which structure provides an excitatory input to the ipsilateral abducens nucleus for saccades?

Pontine reticular formation Signup and view all the answers

What type of eye movement characterizes true optokinetic nystagmus (OKN)?

Rhythmic involuntary conjugate ocular oscillation. Signup and view all the answers

What is the primary function of vergence movements?

To align the eyes on an object approaching or retreating Signup and view all the answers

Which statement about divergence is correct?

It is less dynamic than convergence. Signup and view all the answers

What role do the otoliths (utricle and saccule) play in eye movements?

They respond to linear acceleration and static head tilt. Signup and view all the answers

Which type of eye movement is essential for binocular single vision?

Vergence Signup and view all the answers

How does the vestibular system contribute to eye movements?

It stabilizes the direction of gaze during head movements. Signup and view all the answers

What is a characteristic of active eye movements like vergence?

They can be controlled voluntarily. Signup and view all the answers

Which statement is true about ocular counter-rolling?

It is a response to linear acceleration. Signup and view all the answers

What is the relationship between vergence movements and binocular fusion?

Vergence movements enhance binocular fusion. Signup and view all the answers

What indicates a possible restrictive limitation in eye movement?

Inability to achieve full ductions Signup and view all the answers

What is the term for the deviation of the nonfixating paretic eye in paralytic strabismus?

False image displacement Signup and view all the answers

What condition is more likely to develop amblyopia?

Uncrossed diplopia with esotropia Signup and view all the answers

What should be tested to determine if a conjugate defect has reflexive eye movement?

Oculocephalic reflex test Signup and view all the answers

What type of diplopia is associated with a patient experiencing esotropia?

Uncrossed diplopia Signup and view all the answers

What phenomenon may occur with eye closure in patients experiencing gaze palsy?

Bell phenomenon Signup and view all the answers

Which condition is characterized by a patient learning to suppress the false image?

Developmental amblyopia Signup and view all the answers

What visual complication can arise from persistent gaze palsies?

Permanent visual impairment Signup and view all the answers

What assessment should be performed to evaluate the range of motion monocularly?

Versions test Signup and view all the answers

Which condition is commonly associated with esotropia during recovery due to abducens palsy?

Accommodative esotropia Signup and view all the answers

Which of the following is listed as a common cause of vertical diplopia?

Myasthenia gravis Signup and view all the answers

What is the primary deviation when fixating with the nonparetic eye in incomitant strabismus?

Angle of misalignment Signup and view all the answers

Which of the following is identified as a less common cause of vertical diplopia?

Wernicke encephalopathy Signup and view all the answers

Which cause of esotropia is directly related to an increase in convergence tone due to cerebellar dysfunction?

Chiari malformation Signup and view all the answers

Which condition is characterized by the presence of a spastic phase in cyclic oculomotor palsy?

Accommodative esotropia Signup and view all the answers

Which syndrome is described as having an associated abduction deficit and hypometric saccades?

Stiff person syndrome Signup and view all the answers

Which type of eye movement disorder is linked to orbital infiltration or lymphomas?

Orbital inflammation myositis Signup and view all the answers

What condition is associated with a risk of double elevator palsy?

Congenital muscle fibrosis Signup and view all the answers

What primarily rotates the eyes directly upward?

Superior rectus Signup and view all the answers

What is the maximum angle of esotropia that is typically expected to resolve without surgery?

40 prism diopters Signup and view all the answers

At what age is early correction of strabismus shown to improve visual cortical development?

Before 11 months Signup and view all the answers

Which muscle action primarily causes excyclotorsion of the affected eye in the event of a superior oblique palsy?

Unopposed action of the inferior oblique Signup and view all the answers

What is the typical degree of incyclotorsion caused by the superior oblique muscle?

5 degrees Signup and view all the answers

What condition is often associated with constant esotropia after 3 months of age?

Developmental delay Signup and view all the answers

Which treatment option is common for managing intermittent exotropia?

Exercises and minus-lens spectacles Signup and view all the answers

What type of deviation can ocular torsion help differentiate?

A superior oblique palsy from skew deviation Signup and view all the answers

Which muscle assists the inferior rectus in rotating the eyes directly downward?

Inferior oblique Signup and view all the answers

Study Notes

Optokinetic System and Vestibular System

The optokinetic system supplements the vestibular system during sustained rotations.
OKN (optokinetic nystagmus) is characterized by rhythmic involuntary conjugate eye oscillation.
A lateral head turn induces movement in the endolymph of the horizontal semicircular canal, exciting the contralateral abducens nucleus while inhibiting the ipsilateral abducens nucleus.

Elicitation of OKN

Movement can be provoked by dynamic visual stimuli, such as a rotating image of the environment.
Bedside tests for OKN evaluate foveal pursuit and refixation saccades, requiring the subject to simply look at the stimulus without tracking its motion.
Slow and quick phases of eye movement are assessed in response to stimulus motion.

Vergence Movements

Vergence movements (convergence and divergence) maintain ocular alignment for binocular vision on approaching or retreating objects.
Electromyography shows divergence is an active movement, though less dynamic than convergence.
The vestibular system stabilizes gaze during head movements by modifying tonic input to ocular motor nuclei.

Ocular Misalignment Evaluation

Examine for abnormal resting head turns or tilts and assess ranges of versions and ductions to identify ocular misalignment.
Ductions refer to monocular eye movement ranges; restrictive limitations may require forced eye movement testing.
Conjugate defects, like gaze palsy, need to be evaluated for reflexive eye movements.

Amblyopia and Visual Impairments

Suppression of a false image in cases of strabismus can lead to developmental amblyopia if it occurs before visual maturity.
Esotropia is more likely to result in amblyopia than exotropia due to fixation challenges.

Causes of Esotropia

Includes conditions like abducens palsy, accommodative esotropia, and congenital forms among others.
Additional factors may include myasthenia gravis and various ocular muscle restrictions due to orbital issues.

Causes of Vertical Diplopia

Common causes include superior oblique palsy and thyroid eye disease.
Other less frequent causes involve orbital inflammation, myasthenia gravis, and structural abnormalities due to various syndromes or conditions.

Strabismus and Treatment

Primary deviation refers to the angle of misalignment when fixating with the nonparetic eye.
Correcting strabismus before 11 months improves visual cortical development, while constant esotropia after 3 months often signals underlying developmental issues.
Treatment strategies for intermittent exotropia can include exercises, spectacles, or surgical interventions.

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Description

This quiz explores the evolutionary relationship between the optokinetic system and the vestibular system during sustained rotations. Test your knowledge on how visual stimuli trigger involuntary ocular oscillations and the physiological mechanisms involved.