biig booty thad em 3

hes a lil princess

define fixational eye movements and why we study them

miniature or micro-eye movements (eyes are constantly moving as we fixate on a target)
we study them to determine normal from non-normal
people have LASIK (imagine if eye moved in a way we didn’t want)

what are the 3 types of normal fixational eye movements?

tremor
drift
microsaccades

describe tremor
frequency (how often movement happens, measured in hz)
amplitude ( measured in ‘/’’ of arc) —> larger amplitude = bigger eye movement
function

30-100 hz
5-30’’ of arc
considered noise

Describe drift
frequency (how often movement happens, measured in hz)
amplitude ( measured in ‘/’’ of arc) —> larger amplitude = bigger eye movement
function

1-8’/ sec (mean is 5’/sec) —> more of a velocity but whatevs
2-5’ of arc
Drift is the eye wandering away, but there is a chance it may be wandering in a slightly controlled direction, slowly nudging the eye back toward the target. probably noise but may be error correcting, does NOT obey Herring’s law of equal innervation (each eye may drift independently)

Describe microsaccades
frequency (how often movement happens, measured in hz)
amplitude ( measured in ‘/’’ of arc) —> larger amplitude = bigger eye movement
function

1-2 per second
mean is 5’ of arc (range is 1-25’ but rarely above 10’)
usually error correcting, and this does obey Herring’s law of equal innervation.

How does fixation variability change with fixation time?

The area over which fixation varies increases with fixation time (longer fixation = more variable).

what do the normal fixational eye movements look like on a time (sec) x 5’’ arc direction graph

Define directional bias of fixation

fixation tends to vary more along one direction of gaze

What is the stabilized retinal image technique?

Eye movements are tracked and the image moves with the eye, so the image stays stationary on the retina regardless of eye movement.
Technique to determine what micro-eye movements are really for

What happens to a stabilized retinal image?

When first presented it is seen clearly, but within a few seconds it fades to a blank field. This disappearance is mostly permanent. unless stabilization is imperfect or illumination varies.

Q: What is the Troxler effect?

Fading of a stabilized retinal image that can occur with careful fixation even without special apparatus. think dr heartthrob

Which fixational eye movements prevent the Troxler effect?

Microsaccades —simulating tremor and drift contribute little; movements similar to microsaccades produce much greater improvement in visibility.

Why are microsaccades less critical when the head is free to move?

Natural head instability provides retinal image velocities equivalent to those microsaccades provide when the head is fixed.

What are the 3 categories of abnormal fixation?

slow drift
saccadic intrusions
nystagmus

What are 5 causes of acquired fixational abnormalities?

Stroke
tumor
aneurysm
infection
MS (especially with lesions in the brainstem, cerebellum, or vestibular system)

When should you refer if unsure whether a fixation problem is acquired or congenital?

Always refer for additional testing if uncertain. THINK FOGT

What condition is slow drift commonly associated with?

Amblyopia (monocular phenomenon)

Define slow drift in terms of:
velocity
amplitude
corrected by?

Velocity < 3 deg/sec
amplitude: < 1 deg
probably corrected by saccades

define saccadic intrusions

a type of abnormal fixational eye movement which consists of unwanted saccades that interrupt fixation

what are the 3 types of saccadic intrusions

square wave jerks
macro square-wave jerks
macro saccadic oscillations

Describe square-wave jerks

a type of saccadic intrusion
the eye makes a small jump away from the target, then jumps back after a short delay (amplitude of movement is (0.5-5 degrees)
common in normal healthy people but more frequent amounts suggest cerebellar disease or MS
if no complaints, may monitor

define macro square-wave jerk

a type of saccadic intrusion
does not occur in normal ppl
same idea as square wave jerks but bigger jumps (5-15 degrees)
cerebellar and MS (most common etiology is MS)

Define Macrosaccadic oscillations

a type of saccadic intrusion
instead of one jerk away and back like the other two saccadic intrusions, eye makes a series of saccades that gets bigger and bigger, then smaller and smaller, swinging back and forth.
occurs because the brain’s gain controller (system responsible for calibrating how big saccades should be) is misfiring

define nystagmus

a type of abnormal fixational eye movement
could be congenital/ infantile nystagmus (develops within the first few months of life) or acquired rhythmic oscillations of the eye

Describe the two main types of nystagmus waveform

pendular: eye swings back and forth at equal speed in both directions like a pendulum. There is no clear “slow then fast”, it is smooth and sinusoidal
jerk nystagmus: has a distinct pattern : a slow drift in one direction followed by a fast snap back. the slow phase tells you the cause

What are the three types of jerk nystagmus slow phase

constant velocity (sawtooth)
accelerating slow phase
decelerating slow phase (gaze evoked)

Describe Constant Velocity (sawtooth) Nystagmus

the eye drifts off at a steady, even speed then snaps back. (a type of jerk nystagmus)

Describe the physiological causes of constant velocity (sawtooth) nystagmus

physiological causes
post rotary: spinning to the right in a chair.. horizontal fluid blah blah (james in patho)
caloric: warm or cold water/air into ears
optokinetic: normal response… think of the drum
could also be acquired

Describe accelerating slow phase nystagmus

the eye drifts —> brain accidentally accelerates it further—> then has to snap back
almost always congenital

Describe decelerating slow phase (gaze-evoked) nystagmus

in health, when you look to the side the brain has to actively hold eye in eccentric position (called the gaze-holding system)
in gaze evoked nystagmus, eye looks to side—> gaze holding system can’t maintain it—> but as it gets closer to center its easier to hold (so the drift slows down)—→ saccade snaps it back out to where you were trying to look

what causes decelerating slow phase nystagmus (gaze evoked)

physiological: normal if extreme eccentric angles
acquired: MS, cerebellar issues, Alcohol

Describe Latent Nystagmus

a type of jerk nystagmus
special case where nystagmus only appears when one eye is covered (i.e. refraction)
almost always congenital and linked to strabismus
the fast phase always beats towards whichever eye is still open

When does congenital nystagmus appear

within the first few months of life

what conditions are congenital nystagmus associated with

idiopathic
albinism
congenital cataract
retinal disease (Optic nerve hypoplasia)

Describe the null position of congenital nystagmus

every pt has one gaze position where their nystagmus is the calmest (lowest amplitude x freq)
their vision is best here because the eyes are moving the least

Describe periodic alternating nystagmus (PAN)

null shifts around over several minutes or longer
they alternate the direction of their nystagmus= null point can also be switched around depending on which beat of nystagmus they have

T/F: there is often a reduction in nystagmus with divergence

FALSE
reduction in nystagmus occurs with CONVERGENCE (near acuity better)

Describe foveation periods for pts with congenital nystagmus

Brief moments during the nystagmus cycle where the eye happens to be still and on the target. allows patients to have functional vision despite constant eye movement

T/F: patients with congenital nystagmus don’t tend to have oscillopsia

TRUE
in congenital nystagmus the brain develops alongside the nystagmus from infancy, so it learns to ignore the movement entirely

T/F: patients with acquired nystagmus do not tend to have oscillopsia

FALSE
they do, type shit

Explain the abnormal head posture of a pt with congenital nystagmus who has a null point to their left

they turn their heads to the right so their eyes can naturally sit in left gaze, which puts them right at their null point

T/F: acquired nystagmus is typically only horizontal

FALSE
congenital nystagmus is typically only horizontal. acquired can be whatever it wants

describe as many key differences between congenital and acquired nystagmus as you can lol

How can prisms help with management of congenital nystagmus

Prism moves images to the null point to reduce head turn
(e.g., null point to right → prescribe base-left prism).
Base-out (BO) prism increases convergence demand, which also dampens nystagmus.

What is the 2-muscle surgical procedure for congenital nystagmus

moves the eyes (effectively the null point) to primary gaze by weakening muscles antagonizing the null point direction
i.e. null right → weaken right LR and left MR).
The example: null point is to the right
Patient currently has to look right to be at their null point
So they turn their head LEFT to get their eyes looking right
We want their null point at center instead

What is the tenotomy/4-muscle procedure (Dr. Hertle)?

All 4 horizontal recti are detached and reattached at the same location (or repositioned)
this dampens nystagmus for reasons not fully understood.

What is the clinical rule for acquired nystagmus regarding referral?

acquired nystagmus is not normal
if you cannot prove it is congenital you must refer

What are some causes of acquired nystagmus?

stroke
tumor
aneurysm
infection
MS lesion in brainstem/cerebellum/vestibular
alcohol intoxication
medications (phenytoin, dilantin, sedatives)

Info on alcohol and horizontal gaze nystagmus test with roadside sobriety testing. not sure if important (prolly not)

What is visuoscopy used for?

to assess fixation quality (steady vs unsteady, central vs eccentric) using a direct ophthalmoscope with bullseye fixation setting

How is visuoscopy preformed

pt monocularly fixates the target on the DO, and the examiner views the target imaged on the retina.
if the foveal reflex is centered in the target = central fixation

What type of eye movements is it harder for visuoscopy to detect

normal fixational eye movements
drift
tremor
microsaccades
need an eye tracker to detect these

what eye movements can visuoscopy detect?

slow drift
saccadic intrusion
nystagmus

what is an eccentric point

retinal location the patient is using to fixate ( where the object of regard is imaged when it is not on the fovea)

what is an eccentric fixation?

the fovea is still intact but the brain has been required (usually from strabismus/amblyopia) to treat a different retinal point as straight ahead.
pt believes they’re looking directly at the target but they are not.
we want to fix this bc it is a mistake visual system is making

what is eccentric viewing?

the fovea is damaged (central scatoma), so looking straight at something makes it disappear into the blind spot.
pt deliberately learns to looks lightly off-center to use a healthier part of their retina
we use this as a coping strategy for them

How is eccentric fixation magnitude reported in visuoscopy?

in prism diopters (PD)
you must know the calibration of your DO target (project on a wall at 1m: 1cm separation= 1PD?)
must be able to do example!!

Who typically has eccentric fixation?

strabismic amblyopes (monocular phenomenon only)

How does eccentric fixation affect clinical testing?

it affects any test requiring monocular fixation (e.g cover test)

what is the formula for estimating VA from eccentric fixation magnitude?

MAR= EF +1
EF: eccentric fixation in prism diopters

What VA does EF = 0 predict?
EF = 1 PD?

EF = 0 → MAR = 1’ → 20/20
* EF = 1 PD → MAR = 2’ → 20/40

Can a pt with 20/20 vision have eccentric fixation?

No, 20/20 rules out eccentric fixation

What is clinical angle kappa measuring

the linear distance between the corneal reflex (1st purkinje image) and center of entrance pupil during monocular penlight fixation. In layman terms: way of estimating where the fovea is by looking at where light reflects off the cornea relative to the center of the pupil.
note: not a true angle ( we do not measure the visual axis vs pupillary axis directly)

What is the sign convention for angle kappa?

Reflex nasal to center of entrance pupil= positive (+)
Reflex temporal to the center of the entrance pupil= negative (-)
mean normal is +0.5

What does a shift of 1mm in corneal reflex position equal is prism diopters (PD)

22 PD (12 degrees)

What is the main clinical use of angle kappa

to rule out retinal disorders casuing a “dragged fovea”

Angle kappa example: reflex is 1mm nasal OD what does this indicate?

indicates 11 PD temporal eccentric fixation ( since normal is +0.5 mm nasal)
the patient is now fixating a point nasal to where the fovea used to be= nasal retinal point = nasal eccentric fixation

Angle kappa example: Reflex is centered (0.00mm). what does this indicate

indicated 11PD nasal eccentric fixation (since normal is +0.5 mm nasal)
reflex is actually 0.5mm more temporal than expected, indicating nasal eccentric fixation

What is the Hirschberg test?

a binocular version of angle kappa
an objective test for strabismus
patient fixated on a penlight binocularly; examiner notes corneal reflex position in each eye

how is the Hirschberg result recorded?

as an angle of deviation (in PD)
must compare to angle kappa (assuming angle kappa is +0.5mm OU)

Hirschberg example: reflex 1mm temporal OD , 0.5 mm nasal OS. What does this mean

OS is fixating normal
OD reflex is reflex is fitting too far temporal = right esotropia (33 PD)

Hirschberg example: 4mm pupil (normal angle kappa)