semester 2 Eye: Movements

what are the five types of eye movements

1. saccadic

2. smooth pursuit

3. optokinetic

4. vestibular

5. fixational

6. vergence

how many axes do ocular eye movements occur

3 (x , y and z)

which axes has horizontal eye movements

y axis

what are y axis movements called

elevation and depression

What is movement on the x axis

cyclooctadiene eye movements

what are x axis movements called

torsional ( intorsion or extrosion )

What movement is about the z axis

horizontal eye movements

what are z axis movements called

adduction and abduction

what is the field of fixation

40- 50 degrees

what are typical eye movements in degrees

15

what are saccadic movements

rapid, jerky eye movements that occur between fixations

what is the purpose of saccadic movements

1. Bring images of interest onto the fovea

2. Allow us to sample visual environment

what are the peak velocities of saccadic eye movements

500 - 700 degrees / second

most saccadic eye movements are completed in

300 m sec

The larger the eye movement the ______ it is

faster

what type of eye movement is a typical response to the visual environment

saccadic eye movements

how are saccadic eye movements evaluated

asking a patient to look from one object to another in quick succession in either horizontal or vertical directions

what interferes with saccadic eye movements

ablation ( destruction of body tissue) of both structures

what controls saccadic eye movements

neural commands

what is saccadic suppression

where visual processing is temporarily reduced during rapid eye movements (saccades) to prevent blurry or jumbled images

what is smooth pursuit

eye movement that allows us to track a moving object smoothly and steadily

where is smooth pursuit found

accessory optic system, brain stem reticular formation, cerebellar flocculi and parietal lobes

what is vergence

to move the eyes in opposite directions to place images of a single object on both foveae

what is a version compared to a vergence

versions= movement of 2 eyes in the same direction

vergence: synchronous eye movement of 2 eyes in opposite directions

what is the maximum velocity of a vergence

20 deg / sec

what is the main purpose of vestibular and optokinetic system

maintain a stable retinal image during head movements

what sensory signals generate Vestibular (VOR)

from the ear and neck ( head movement )

what sensory signals generate optokinetic eye movements

retinal signals

which eye movement is a result of a repeating pattern Infront of the eyes

Optokinetic

what happens during sustained rotation

VOR holds eyes steady during first few seconds, then VOR declines (mechanical characteristics of semi-circular canals) and OKN (optokinetic nystagmus) is then stimulated to help prevent image movement.

what is a nystagmus

what is fixational eye movements

movements maintaining the retinal image of an object on the centre of the fovea

what are the types of fixational eye movements

1. tremors

2. drifts

3. micro saccades

what are tremors fixational eye movements known as

physiological nystagmus

what is the smallest eye movement

tremor fixation

what is a drift fixational eye movement

small eye motions of around 2-5 min arc that occur in between microsaccades

when do drifts occur

when microsaccades are poor or absent

which fixation eye movements occur simultaneously

drifts and tremors

what are micro saccadic fixational eye movements

larger, voluntary saccades, which are rapid eye movements that we make when shifting focus from one object to another

what are micro saccades also known as

flicks

what are the methods used to measure eye movements

• Direct observation of the eyes.

• The EOG (electro-oculogram).

• Infra-red reflection methods.

• Video systems

• Scleral search coil (research)

• Purkinje eye tracker (research)

• relies on on cues from more than 1 surface of the eye, not just cornea

what does an electro-oculogram do

records the eye position using electrodes attached to the face. From the Inner and outer canthi to record horizontal movements

how does the search coil measure eye movements

• A coil is embedded in a contact lens annulus that is placed on the eye.

• The patient is then placed in a magnetic field.

• As the eye moves, there is a current induced in the coil. The current is proportional to the eye movement.

what is the most common method used in eye movement tracking

infra red

how does infra red allow eye movement to be measured

• the detection of reflected infra-red light from the anterior eye by sensors.

• The reflection from the cornea is tracked relative to the pupil centre.

• The sensors can be mounted onto spectacle frames which can be useful to remove the influence of head movements.

• As the eye moves from one side to the other, the amount of light detected changes and is proportional to the eye movement

how many extraocular muscles control eye movement

6

what are the names of the extraocular muscles controlling eye movement

1. medial rectus

2. lateral rectus

3. superior rectus

4. inferior rectus

5. superior oblique

6. inferior oblique

where do the eye movement muscles attach

at the apex of the orbit except the inferior oblique

what are rotations of a single eye called

ductions

what are the types of ductions

1. abductions

2. adduction

3. sursumduction

4. deosursumduction

what direction is an elevation duction

upwards

what direction is a depression duction

downwards

Rotations about the anterior-posterior axis are called

torsions

what is an intorsion

movement from the top of the eye towards the nose

what is an extorsion eye movement

movement from the top of the eye away from the nose ( temporally)

which muscles are responsible for horizontal eye movements

medial and lateral rectus

which direction does adduction move the eye

towards the nose ( nasally)

which direction does abduction move the eye

away from the nose ( temporally)

which muscle is responsible for abduction

lateral rectus

which muscle is responsible for adduction

medial rectus

which muscle is responsible for elevation

superior rectus

which muscle is responsible for depression

inferior rectus

which muscle is responsible for intorsion

superior oblique

which muscle is responsible for extorsion

inferior oblique

what is sherringtons law

the state of contraction in the agonist regulates the state of contraction in the antagonist.

What is a agonist muscle

muscle responsible for movement

what is an antagonistic muscle

produces a movement in the direction opposite to the agonist

what is a ballistic eye movement

once the eye moves we cannot amend magnitude or direction if the stimulus changes

what is a pursuit movement

movement of the eye requiring a near foveal moving target