Lab 4: Electrooculogram

Arden ratio

________ (light peak /dark trough)- can be used to detect some conditions (vitelliform macular degeneration, etc .)

Light adaptation

breakdown of photosensitive pigments due to intense light exposure decreases receptor sensitivity allowing normal contrast to be seen under conditions of intense light

Dark adaptation

regeneration of photosensitive pigments in absence of intense light increases receptor sensitivity allowing contrast to be seen in low light conditions

Arden ratio (light peak/dark trough)

can be used to detect some conditions (vitelliform macular degeneration, etc.)

Saccades

short, jerky (ballistic) movement of the eyes (saccadic movement)

Fixation

Locking the eyes onto an object

80

90% of the time

Voluntary fixation movement

conscious unlocking of the eyes from one object in order to move them to another object

Involuntary fixation movement

Unconscious movement of the eyes to follow an object they are locked onto as it moves

Track can become smooth (pursuit movement

slower and smother than saccades) if the object is moving in a regular pattern that the brain can learn and predict

Drift

slight movement of the eyes due to the inability of the ocular muscles to hold the eyes perfectly still

Microsaccades

Very small jerky eye movements thought to compensate for drift, and return the "locked" object to the center of the field of vision

Physiological nystagmus (tremor)

slight tremor of the eyes

Vision and Balance

brain uses information from vestibular apparatus and vision to determine body position in space

Rotational nystagmus

abnormal condition, "Bouncing" of the eyes back and forth (or up and down) in response to continued movement of fluid in the vestibular apparatus of the inner ear when the head has stopped spinning

Vestibulo-ocular reflex

Eyes move opposite to of head movement to maintain fixation on an object

What measures the resting potential of the retinal pigmented epithelium?

electroculogram

The eye presents as a ___.

dipole

The eye is ___ in the front and ___ in the back.

positive; negative

How can shifts in eye position be detected?

shifts in the angle of the dipole relative to sets of electrodes

True or False: Shifts in eyes causes an electrical flow.

True

During light and dark adaptation, shifts in ___ can be recorded and used to diagnose various conditions.

retinal potential

What occurs during light adaptation?

breakdown of photosensitive pigments due to intense light exposure decreases receptor sensitivity allowing normal contrast to be seen under conditions of intense light

increase light -> decrease pigment -> decrease sensitivity

What occurs during dark adaptation?

regeneration of photosensitive pigments in absence of intense light increases receptor sensitivity allowing contrast to be seen in low light conditions

decrease light -> increases pigment -> increase in sensitivity

What is an arden ratio?

ratio of light peak vs dark trough

What is used to detect conditions such as Best's disease and vitelliform macular dystrophy?

arden ratio

Saccades, drift, microsaccades, physiological and rotational nystagmus, voluntary and involuntary fixation movement are all examples of ___.

eye movements

What are saccades?

short, jerky (ballistic) movement of the eyes - jump from one object to another

True or False: Brain receives input during a saccade.

False - brain ignores input to prevent blurring

What is fixation?

locking eyes onto an object

True or False: Eyes are fixated or "locked" between saccades 80-90% of the time.

true

In order to an object, eyes must be ___.

fixated

Why does the brain ignore input from retina while eyes are in motion?

prevents blurring of the image

What is voluntary fixation movement?

conscious unlocking of the eyes from one object in order to move them to another object; movement occurs in saccades

What is involuntary fixation movement?

unconscious movement of the eyes to follow an object they are locked onto as it moves

As an object moves, how does the brain "follow" during involuntary fixation movement?

brain anticipates the object's path and moves the eyes in saccades along that projected path ahead of the object in order to keep up with it

If an object's path is smooth and regular, then eye movement can become smooth and regular called ___

pursit movements

True or False: Saccades are slower and smoother than pursit movements.

False - saccades rapid, pursit slow

What is drift?

slight movement of the eyes due to the inability of the ocular muscles to hold the eyes perfectly still

What can cause the illusion that a single point of light is in motion?

drift

What are microsaccades?

very small jerky eye movements that return the "locked" object to the center of the field of vision

What does microsaccades compensate/correct?

drift

What is a physiologcal nystagmus?

slight tremor of the eyes that is normal and imperceptible to the naked eye

Brain uses information from ___ and vision to determine body position in space.

vestibular apparatus

What is binocular vision/depth perception used for?

to determine postion in space relative to objects in visual field

Vertigo and motion sickness is caused by?

conflicts in info from eyes and ears; inability of eyes to lock onto an object when the brain expects to be able to

What detects head movement in relation to gravity and inertia?

vestibular apparatus, saccule, and utricle

What is rotational nystagmus?

"bouncing" of the eyes back and forth (or up and down) in response to continued movement of fluid in the vestibular apparatus of the inner ear when the head has stopped spinning; abnormal and visible

True or False: Physiological nystagmus is abnormal and visible and rotational nystagmus is normal and not visible.

False - Physiological is normal/not visible and rotational is abnormal/visible

What is vestibulo-ocular reflex?

eyes move opposite to of head movement to maintain fixation on an object