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148 Cards in this Set
- Front
- Back
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Abduction is the tertiary action of what muscles? Adduction is the tertiary action of what muscles?
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Abduction - tertiary action of obliques
Adduction - tertiary action of recti |
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The recti insert anteriorly at ____degrees. The superior oblique inserts posteriorly at _____degrees and the inferior oblique at ______degrees.
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Recti: 23 degrees
Sup oblique: 54 degrees Inf oblique: 51 degrees |
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Laws of eye movement:
1. Hering's (yoked muscles?) 2. Donder's 3. Listing's 4. Sherrington's (paired agonists?) |
1. Muscles are equally innervated when working to move the eye; muscles work in pairs to move the eye
PAIRED muscles: LR/MR, SR/IO, SO/IR 2. Path or starting location is not important for orientation of final destination. 3. Eye moves along an axis within Listing's plane to get to a non-primary position. 4. Agonist and antagonist EOM's of the SAME eye are reciprocally innervated (one stim, one inhib) *PAIRED agonists: SR/IR, IO/SO, LR/MR |
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Which has the longest latency, but also the fastest velocity?
Saccades Smooth pursuit Vergence Vestibular reflex |
Saccades - 200msec latency, 1000deg/sec velocity
_______________________________ Vergence - latency 160msec, velocity 10 deg/sec Smooth pursuit - 125msec latency, 50deg/sec velocity Vestib reflex - 15msec, 300deg/sec (SHORTEST LATENCY) |
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_______ are the fastest eye movements and act to correct errors in monocular fixation produced by spurious microdrifts and saccades.
______ are yoked eye movements used for reading. |
Microtremors
Microsaccades |
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What is the slowest corrective eye movement?
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Microdrift (1arcmin/sec)
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OKN replaces VOR after _____sec of sustained head rotation.
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30 sec
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VOR circuit (direct and indirect p'ways)
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Direct p'way drives VELOCITY of eye rotation:
1. Semicircular canals detect head rotation and drive rotational VOR (main p'way; otoliths detect head translation and drive translational VOR) 2. Canals send impulse via CNVIII (through Scarpa's ganglion) to the vestibular nuclei in the medulla/pons 3. Vestibular nerve fibers CROSS to contralateral side and project to CNVI nucleus (abducens) for eye movement to opposite side head rotation 4. Also project to CN3 via MLF for conjugate eye movement Indirect p'way drives POSITIONAL signal to hold eye away from center: 1. Neural integrator for horizontal eye position found in nucleus prepositus hypoglossi in the MEDULLA 2. Neural integrator for vertical eye position found in interstitial nucleus Cahal (INC) in the MIDBRAIN *Note that these same neural integrators generate eye position for saccades and smooth pursuit |
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Caloric testing
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For assessing vestibular dysfunction (tests VOR)
Warm water poured into right ear causes eyes to move slowly left, with a resulting fast corrective saccade (producing horizontal nystag) Cold water in the right ear produces the opposite effect - fast movement to the left side "COWS" - cold opposite / warm same, referring to the FAST saccadic movement (think this is normal, and pathologic is defined by slow) ____________________________________ If the water is warm (44°C or above) endolymph in the ipsilateral horizontal canal rises, causing an increased rate of firing in the vestibular afferent nerve. This situation mimics a head turn to the ipsilateral side. Both eyes will turn toward the contralateral ear, with horizontal nystagmus to the ipsilateral ear. If the water is cold, relative to body temperature (30°C or below), the endolymph falls within the semicircular canal, decreasing the rate of vestibular afferent firing. The eyes then turn toward the ipsilateral ear, with horizontal nystagmus (quick horizontal eye movements) to the contralateral ear Absent reactive eye movement suggests vestibular weakness of the horizontal semicircular canal of the side being stimulated. |
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T/F: pendular nystagmus has a slow phase and a fast, corrective phase
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F
This is jerk nystagmus. Pendular nystag shows an even back-and-forth movement |
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T/F: physiologic nystagmus tends to be conjugate
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T
"conjugate" meaning both eyes move together |
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What CNS pathologies may show nystagmus?
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Brainstem & cerebellar disease!
From stroke, tumor at cerebellopontine angle, multiple sclerosis, drugs (e.g. anticonvulsants like phenytoin) |
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What are three peripheral vestibular etiologies of nystagmus?
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Labyrinth diseases:
1. Benign paroxysmal positional vertigo (BPPV) 2. Vestibular neuritis 3. Gentamicin toxicity (occurs if unilateral) |
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Besides vestibular disease, brainstem/cerebellar pathology, and a congenital etiology, what else can cause nystagmus?
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Visual loss
"Sensory nystagmus" caused by poor/absent vision *Impaired vision can cause nystagmus, and nystagmus can cause impaired vision!* |
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Which is more visually-disturbing, jerk or pendular nystagmus?
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Pendular
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We should always describe nystagmus in terms of what 3 characteristics?
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Direction
Amplitude (mm or deg) Frequency (low = see-saw; medium = congenital; high = spasmus nutans) |
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Vertical nystagmus is always pathological. We worry most about what condition?
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Arnold-Chiari malformation - downward displacement of the cerebellar tonsils through the foramen magnum
Usually a DOWNBEAT nystagmus The etiology is generally something at the cervicomedullary junction Other etiologies include vestibulocerebellum degeneration, MS, drug toxicity (lithium, EtOH, phenothiazenes) |
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What do we suspect when we see "see-saw" or "boogie-woogie" nystagmus?
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Parasellar mass (e.g. pituitary tumor)
One eye beats up and intorts, the other beats down & extorts Also due to midbrain lesion (INC), septo-optic dysplasia (a.k.a. DeMorsier Syndrome, a malformation characterized by optic disc hypoplasia & absence of septum pellucidum) |
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If nystagmus is only present in upgaze, what might we suspect?
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MG
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Etiology of gaze-evoked nystagmus?
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Saccade signaling:
Need “burst” to get eyes to look eccentrically – burst neurons do this Need “step” to keep them there – neural integrator does this *Horizontal saccade integrator = NPH, MVS in pons/upper medulla *Vertical saccade integrator = INC in midbrain If the neural integrator is lesioned, the eyes are able to make an eccentric saccade but then slowly drift back to straight-ahead The “leaky” neural integrator is unable to keep eyes in eccentric gaze, and the viscoelastic forces of the orbit return the eyes to center (suspensory ligaments, EOMs, etc) The eyes then make another saccade to the eccentric position, drift back to center, etc. |
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Which nystagmus shows quick phase in the direction of gaze?
Which nystagmus does not change with direction of gaze? |
Gaze-evoked nystagmus
Peripheral vestibular nystagmus |
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Peripheral vestibular nystagmus beats (away/towards) the lesioned ear.
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Away
*E.g. right-ear lesion -Brain interprets signal imbalance between the ears as the head moving to the left (stronger signal) -Eyes make compensatory drift to the right (towards the lesion) -Quick beat to the left |
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Spasmus nutans shows what classic triad?
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1. Head turn
2. Head nodding 3. Nystagmus Beings within first year of life (usu 6 months) and lasts about a year Key feature is that the nystagmus is benign and self-limiting – gone by age 2-3 (certainly no later than 5-8) Nystagmus is described as a “shimmering nystagmus” due to low amplitude, high frequency Spasmus nutans nystagmus is UNILATERAL or asymmetric, intermittent, often worse in abduction and if the head is kept still, and disappears with closed eyes Should refer to r/o glioma - unilateral gliomas can cause acquired monocular pendular nystagmus that is practically indistinguishable from spasmus nutans (though other afferent p’way signs are often present with glioma also) |
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Characteristics of congenital nystagmus? (SLAM-FAN)
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-Symptomless (no oscillopsia)
-Latent component -Abnormal OKN (either absent, or both fast phases – nystagmus waveform is reversing) -Mixed waveform (pendular and jerk) -Worsens with Fixation -Always horizontal -Diminishes in Null zone (often convergence) = adaptive head postures |
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T/F: congenital nystagmus can be vertical
T/F: congenital nystagmus is always jerk Congenital nystagmus is lessened by _____ and _____, and worse by ________. |
F
F - can be jerk, pendular, or mixed waveform Convergence and eye closure lessens congenital nystagmus Distance fixation worsens congenital nystagmus |
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Latent nystagmus beats (towards/away from) the eye that's occluded. It is most highly associated with what?
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Away
(beats away from the nose) Associated with infantile esotropia |
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Cochlea vs semicirculuar canals (what does each detect?)
Function of the otolith organs? |
Cochlea detects sound
Semicircular canals detect head rotation Otoliths = utricle & saccule; maintain balance along w/ canals; use small stones and a viscous fluid to stimulate hair cells to detect motion and orientation. |
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What is convergence-retraction syndrome associated with?
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DMS
Jerk movements occur w/ attempted convergence or upgaze |
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(Nasal-to-temporal or temporal-to-nasal?) OKN reflexes are absent until the age of 3-4 months.
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Nasal to temporal
Infants only show nasalward OKN since cortical OKN regions have not yet developed |
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What are some causes of congenital sensory nystagmus?
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Retinal disease – ocular albinism, Leber’s, achromatopsia, congenital stationary night blindness, cone dystrophy
ON disease - hypoplasia, coloboma Anterior segment opacities, aniridia High refractive errors, including astigmatism |
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Damage to the left FEF impairs saccadic movement to the (left/right).
Damage to the SC affects what aspects of saccadic movements (2)? |
Left FEF lesion = rightward saccade deficit
SC is involved in saccadic accuracy and speed |
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What is ocular flutter, and what test detects it?
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Ocular flutter is 3-4 spontaneous, conjugate saccades in row during the DEM test
DEM = Developmental Eye Movement test, assessing quality and accuracy of saccades |
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What speed is the upper limit for ocular pursuits?
What is the latency and upper speed-limit for saccadic eye mvts? |
50 deg/sec
200msec latency, 1000deg/sec |
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What is the stimulus for each of following vergence movements?
Tonic Proximal Fusional Accommodative |
Tonic - no stimulus; eye's position of rest, measured as corrected distance phoria
Proximal - awareness of nearing target Fusional - retinal disparity Accommodative - blur |
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A (phoria/tropia) only exists under dissociated conditions, while a (phoria/tropia) exists under associated conditions.
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Phoria
Tropia |
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Where should a patient look to isolate the obliques during motility testing? Recti?
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Adduct to isolate the obliques
Abduct to isolate the recti |
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Primary vs secondary deviation in noncomitant strabismus
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Primary deviation - deviation of the paretic eye when the normal eye is fixating
Secondary deviation - deviation of the normal eye when the paretic eye is fixating; typically LARGER than the primary deviation due to Hering's law |
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T/F: the amount of deviation seen in noncomitant strabismus depends on which eye is fixating
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T
(primary vs secondary deviation) |
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Duane's retraction syndrome (3 types)
Important DDx? |
Congenital condition caused by abnormal deviation of CN6 and LR innervation by CN3
Eyes retract into orbits on lateral gaze w/ palpebral fissure narrowing Type 1 - limited ABDUCTION Type 2 - limited ADDUCTION Type 3 - both DDx includes CN6 palsy |
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Brown's syndrome
DDx? |
A.k.a. SO tendon sheath syndrome
SO muscle and tendon/ trochlea abnormality resulting in LIMITED ELEVATION UPON ADDUCTION (restrictive etiology) Small hypertropia in primary gaze, V-pattern exo, widening palpebral fissure on adduction Acquired (scarring, inflammation, iatrogenic) or congenital (SO too short or inelastic tendon) Biggest DDx is IO paresis. Also SO over-action and orbital floor fracture **IO paresis shows ductions>versions, A-pattern exo, SO overaction **Brown's shows ductions = versions, V-pattern exo, no SO overaction |
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What is the pi phenomenon?
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Subjective cover test
A patient with a heterophoria perceives movement in the opposite direction to covered eye's deviation, as it is uncovered. E.g. esophore will see object move right when the right eye is uncovered, exophore will see object move left when the right eye is uncovered |
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Prism set-up for von Grafe phoria measurement
Which image does each eye see? How do you test horizontal phoria? Vertical? |
12 BI over OD, 6 BU over OS
OD will see image up and to the right, OS will see image down and to the left Decrease 12BI to test horizontal phoria Decrease 6BU to test vertical phoria |
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T/F: The Maddox rod test can differentiate a phoria from a tropia
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F
Only determines direction of eye alignment |
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In a right hyper deviation, where is the red line in relation to the white light in the Maddox rod test? Left hyper?
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Line is below the white spot in R hyper
Line is above the white spot in L hyper (or spot is below the red line - remember red lens is over R eye!) |
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T/F: fixation disparity testing is done under dissociated conditions
Describe test. |
F
Fixation disparity testing is done binocularly and detects subclinical misalignment of the visual axes. Subclinical since they fall w/in Panum's fusional area. OD see one line and OS sees another. Prism are used to neutralize the perceived misalignment to find the associated phoria. Direction of associated phoria usually matches direction of dissociated phoria - if not, called a PARADOXICAL FD. |
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What is the most common shape of the fixation disparity curve?
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Sigmoidal (= asymptomatic)
FD curve shows amount FD on the y-axis and associated phoria on the x-axis |
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Calculated AC/A equation
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ACAcalc = PD + h(Pn - Pd)
where PD is in cm, h = distance near target in m, Pn = near phoria, Pd = distance phoria Units are pD / D SIGN CONVENTION: esophoria is positive exophoria is negative |
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Gradient AC/A equation
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ACAgrad = (P1-P2) / (SA1 - SA2)
where P is phoria under 1st and 2nd conditions and SA is stimulus to accommodation under 1st or 2nd condition SIGN CONVENTION esophoria is + exophoria is - Note this is just difference in phoria / difference in accommodation! Use +1.00 lens and re-measure phoria to find gradient AC/A |
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Blur accommodation responds best to blur under what diopter value?
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2.00D
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Blur during smooth vergence testing indicates what?
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When the system is free of accommodation (accommodation gives out)
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Always test (BI/BO) first during vergence testing.
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BI
Testing BO first may induce prism adaptation. |
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Expected findings for smooth vergence testing (~rounded Morgan's norms)
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DBI: x/7/5
DBO: 10/20/10 NBI: 15/20/15 NBO: 17/21/10 (a little higher than BI) |
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Sheard's criterion for comfortable vision
Percival's criterion for comfortable vision |
Vergence (blur point) needs to be twice the phoria for comfortable vision; use break if no blur data is available
Demand should fall w/in middle 1/3 of the zones of clear, binocular vision; fusional vergence should be balanced so that smaller fusional reserve is more than half the larger one |
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Expected findings in fusional vergence testing
Prisms used? |
15 cycles/min
12BO and 3BI |
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NPC expected findings
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5cm break, 7cm recovery
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Expected findings for minus-lens-to-blur amplitude testing?
How to test? |
2.00D less amplitude than push-up method (since minification occurs during this test)
Add minus lenses until patient can no longer clear. Calculate amplitude by adding +2.5D (to account for working distance) |
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Theory behind FCC?
Expected findings for a non-presbyope? |
JCC with minus cyl axis at 90
This gives +0.25D at 90, -0.25D at 180 Theoretically, a patient w/ lag of accommodation will show vertical lines (produced by -0.25D) right behind the retina and horizontal lines (produced by +0.25D) are right in front of the retina If patient reports horizontal lines are clearer than vertical or they are both equal, add plus lenses until vertical lines are clearer --> bringing vertical focus forward onto retina This measure the LAG of accommodation Expected findings are +0.25 - +0.50 D |
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Which 2 Duane-White anomalies show high AC/A? Which 2 show low AC/A?
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High AC/A: CE and DE
Low AC/A: CI and DI |
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Angle lambda is measured by what test? What is normal angle lambda?
A shift of 1mm in the position of the corneal light reflex corresponds to roughly how many pD of deviation? What does the Krimsky test measure? |
Hirschberg test
Angle lambda is the angle between the pupillary axis and the visual axis (LOS), which is normally ~0.5mm nasal Exo shows nasal angle lambda (POSITIVE) Eso shows temporal angle lambda (NEGATIVE) Krimsky test measures deviation w/ prism - match the two eyes w/ neutralizing prism |
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Anomalous retinal correspondence:
Harmonious Unharmonious Paradoxical Type 1 |
ARC is a reassignment of one of they retinal points that are misalignmed from normal retinal correspondence; a "new fovea" is calibrated
Angle of anomaly is the angle by which correspondence shifts Harmonious means angle deviation = angle anomaly (angle of correspondence is perfectly adjusted to the eye's deviation) - MOST COMMON Unharmonious - angle anomaly is LESS than angle of deviation Paradoxical Type 1 - rare condition where correspondence moves in wrong direction relative to deviation |
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Bagolini lens test
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Tests for suppression and retinal correspondence
OD has axis 45 lens (sees \ ) OS has axis 135 lens ( sees / ) X is normal response V is esotropia /\ is exotropia / or \ signifies suppression |
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T/F: the dimmer eye on Bruckner is the fixating eye
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T
OR could be eye w/ high refractive error or media opacity |
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4-BO test
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Looks for microstrabismus (suppression of one fovea)
Place 4BO over one eye, and other eye should make outward shift (due to Hering's law) and then quickly re-fixate Suppression of the other eye's fovea results in no outward movement |
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General characteristics of infantile ET and XT
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Both:
large angle constant alternating minimal refractive error limited BV Infantile ET may show LATENT NYSTAGMUS, INFERIOR OBLIQUE OVERACTION (most common), DVD (a.k.a. alternating hyperphoria; occluded eye goes up!); presence before age 5 and much more common than infantile XT Congenital/Infantile XT is RARE (might consider organic cause first) and rarely shows nystagmus; shows LIMITED ADDUCTION and PANORAMIC VISION; likely occurred after age 5 due to acquired vision loss |
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What is the most common supranuclear dysfunction?
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CI
Seen most commonly in TBI patients, along w/ AI |
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Visual neglect is usually in which hemifield? Due to what?
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Left-sided visual neglect is most common.
Due to right parietal lobe damage |
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Most common causes of non-comitant deviations?
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1. CN 4 palsy
2. CN 3 palsy 3. CN 6 palsy 4. Combo palsy 5. Restrictive ophthalmopathy |
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Advantages & disadvantages of earlier strabismus surgery
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ADVANTAGES:
Better potential for BV Reduced muscle contraction DISADVANTAGES: Increased risk amblyopia Difficulty in obtaining reliable measurements = possibility multiple surgeries *Advantages/disadvantages for later strab surgery are inverse of the above |
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VT in strabismus treatment is most successful with which type of strabismus?
T/F: you should not try VT if there is no fusion |
Intermittent XT
T |
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Best way to Rx vertical prism?
What do you run the risk of when treating an adult stab w/ VT? Use of BOTOX is most widely-accepted when treating what? |
Using FD measurement (allows eyes to have some fusion during testing)
Intractable diplopia Acquired or chronic CN 6 palsy |
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What is the main goal of reverse prism? Relieving prism? Correcting prism?
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Reverse - improve cosmesis by shifting image of the eye for the observer
Relieving - reduce disparity to a manageable level for comfort, e.g. in intermittent strab or Sx phoria Correcting - amt prism correction = magnitude of the strab to completely fix strab that can't be moved with fusion at all (e.g. constant strab or paralytic strab) |
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Muscle resection vs recession
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Resection - TIGHTENING a muscle w/ excision and re-attachment
Recession - detach muscle and move orbital insertion back to SLACKEN muscle |
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25% of patients w/ Goldenhar syndrome also have Duane's. What are some ocular characteristics of Goldenhar?
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Bilateral limbal dermoids
Pre-auricular skin tags Coloboma |
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Moebius syndrome
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Congenital facial weakness + abduction deficit
Due to bilateral absence or maldevelopment of CN VI and VII Also poor saccades, proptosis/ptosis, esotropia w/ no abduction *This is one of the 3 congenital cranial dysinnervation disorders that cause NON-COMITANT strabismus: 1. Duane's 2. Moebius 3. Congenital fibrosis of the EOMs |
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Name 3 restrictive deviations that cause non-comitant strabismus.
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1. Brown's syndrome
2. Thyroid ophthalmopathy 3. Trauma/post-surgical |
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What systemic conditions can cause non-comitant strabismus?
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MS, MG, thyroid disease
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Diplopia worse in the AM is most likely what? Worse in the PM?
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Worse in the AM = thyroid ophthalmopathy
Worse in the PM = MG |
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Order in which muscles are affected in thyroid eye disease?
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IR > MR > LR > SR
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Myasthenia gravis peaks when in females vs males?
What % have ocular MG? T/F: MG never shows spontaneous remission. |
Females: 3rd decade
Males: 6-7th decade 50% F - 30% show spontaneous remission |
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What is the "curtain sign" and Cogan lid twitch"?
What are 2 other ocular signs? |
Signs in MG
-Curtain sign = lift more ptotic lid and the other lid falls a little -Lid twitches upon looking straight after resting lid in downgaze for a short time Intermittent diplopia that changes and is worse in the PM, and gaze-evoked nystagmus |
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What does a psychometric function plot? What is threshold usually defined as?
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% correct or detected vs variable of interest (e.g. light intensity)
Threshold usually set at 50% |
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Automated VF testing usually uses which psychometric method of measurement?
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Stairstep method
Stimulus intensity is increased in stairstep manner, then decreased - this reversal continues for several periods allowing threshold to be defined from both directions; time-efficient! |
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Method of constant stimuli advantage? Disadvantage?
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*Stimulus intensity is randomly varied from presentation to presentation
Observer will not anticipate next stimulus, but this is time-consuming. |
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Which psychometric measurement method should be used for determining dark adaptation?
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Method of ascending limits
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All but one psychometric measurement methods suffer from what drawback? Which test does not suffer this drawback?
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Effect of varied threshold criteria may skew the results since each individual has different criteria
Forced choice method minimizes this |
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Sensitivity vs specificity
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Sensitivity - probability of a test giving a positive result when the signal is present
Specificity - probability of a test giving a negative result when the signal is absent |
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Positive or negative predictive value of a test
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Positive predictive value is probability of signal being present given that the test is positive
Negative predictive value is the probability of a signal not being present given that the test is negative. |
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Mathematically, test sensitivity is _____ / ______.
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# true positives / ( # true positives + # false negatives)
= number diseases detected / total number actual diseases |
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Mathematically, test specificity is _____ / _____.
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# true negatives / (# true negatives + # false positives)
= number detected to be disease-free / total number actually disease-free |
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False negative rate = 1 - ______.
False positive rate = 1 - ______. |
FNR = 1 - sensitivity
FPR = 1 - specificity |
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Receiver operating characteristic curve (ROC) helps determine how _____ affects _______.
How does strict criteria affect the shape of this curve? |
How criteria affects detectability
Plot of correct-detection probability vs false-positive probability The more strict the criteria, the steeper the slope (more correct "hits" with a fewer # false positives) |
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Photometric measurements:
Radiant power Radiant intensity Radiance Irradiance |
*Radiometry deals with energy/time produce by an electromagnetic radiation source*
-Radiant power (W) = energy/sec -Radiant intensity (W/omega) = energy per second in a given DIRECTION where omega is a solid angle = steradian -Radiance is light energy emitted from a particular AREA that falls within a given solid angle in a specified direction, in Watts/steradian/square meter *E.g. how much light (power) does a source of a certain size produce? -Irradiance = radiant power per unit area of surface, e.g. HOW MUCH radiant power HITS OR FALLS ON some object |
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Photometric measurements:
Luminous power Luminous intensity Luminance Illuminance |
*Photometry deals with how our visual system responds to electromagnetic radiation*
Luminous power (lumens) = luminous flux of light produced by a light source that emits one candela of luminous intensity over a solid angle of one steradian In other words, how strongly the visual system responds to light (stronger response = more lumens) We define 680 lumens/W at 555nM For every W of light at 555nM, the visual system responds with 680 lumens -Luminous intensity is luminous power in a given direction (lumens/steradian = CANDELA); deals w/ POINT SOURCES -Luminance is luminous intensity per projected area of source (candela / square meter, in NITS) that deals specificially with EXTENDED SOURCES Can also be measured in foot-lamberts = 3.43 nits -Illuminance is luminous power per unit area of surface (lumens/sq meter or LUX) Can also be measured in foot-candels = 10.8 lux |
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Generally for photometry and radiometry:
Power Intensity Radiance/luminance Irradiance/illuminance |
Power is energy or response / time
Intensity is power in a given direction Radiance/luminance is intensity projected per area of source Irradiance/illuminance is power projected onto an surface area |
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What is the maximum value of luminous power possible?
Given values of luminous efficiency (V), how do we calculate luminous power? |
V = 680 lumens/W (for a 555nM light source) photopic
V' = 1700 lumens/W (for a 555nM light source) scotopic V (680) = luminous power / watt Watt(V) = luminous power |
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Abney's law of additivity
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To get total luminous power, add contributions of all wavelenghts present
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Half-height bandwidth tells what about a filter? High half-height bandwith means what?
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Selectivity of a filter
High half-height bandwith corresponds to LESS sensitive filter |
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T/F: Interference filters allow many wavelengths to pass
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F
Very selective (low half-height bandwith) and essentially only allow one wavelength to pass |
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Sunglasses are often coated with a substance that acts like which type of filter? (minimizes cataract formation!)
Sunglasses act like which type of filter since they minimize amoutn of visible light transmitted? |
Long-pass filter (only long wavelengths are transmitted)
Neutral density filter (transmit all wavelengths equally); sunglasses reduce visible light transmitted = all wavelengths |
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A (Lambert or specular?) surface scatters light equally in all directions.
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Lambert
A specular surface does not scatter light equally = shiny |
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Luminance equation
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L = RE
where R is reflectance factor (dimensionless) and E is illumination (foot-candels) NOTE that this is a linear relationship, and so if illumination is doubled, luminance is also doubled! R is specific to the type of Lambert surface |
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Retinal illumination (T) equation
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T = LA
Units are TROLANDS where L is luminance of viewed surface and A is area of pupil |
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As the distance from a source doubles, illumination changes by a factor of what?
If a surface is tilted by theta, illumination falling on that surface changes by a factor of what? |
E = Icos(theata) / d^2
Illuminance decreases by 4 when distance doubles Illuminance changes by a factor of cos(theta) when the surface is tilted |
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Scotopic vision is characterized by poor acuity and color discrimination, but good _____.
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Sensitivity
(photopic vision is opposite - good VA and color discrimination but poor sensitivity) |
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Principle of univariance
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All info about wavelength of a photon is lost when it's absorbed by a photopigment
Wavelength only determines PROBABILITY of absorption, not the effect |
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At which wavelength are scotopic and photopic sensitivities equal?
This is known as the "point of equal sensitivity" |
650nm
The PHOTOCHROMATIC INTERVAL (diff btwn scotopic & photopic sensitivities) is zero here. |
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Scotopic sensitivity peak? Photopic?
What is the Purkinje shift? |
Scotopic peak at 507nm
Photopic peak at 555nm Purkinje shift is a shift from largely scotopic to largely photopic vision, where longer wavelengths appear BRIGHTER (e.g. red light) as illumination increases. |
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Dark adaptation curve plots what?
What is the rod-cone break on the dark adaptation curve? |
Threshold detection vs time in dark
Break represents change from cone-dominated vision to rod-dominated vision. Note this will be ABSENT FOR 650nM since sensitivities are equal at this wavelength |
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During dark adaptation, decay in sensitivity due to (rods/cones) is very fast while decay in sensitivity due to (rods/cones) is much slower.
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Cones show fast decay in sensitivity
Rods show slow decay in sensitivity |
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Dark adaptation depends on what 3 factors? Eqn?
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1. Fraction of bleached photopigment
2. Threshold intensity for the flash 3. Dark-adapted threshold intensity log (It / Io) = cP where It is threshold intensity, Io is dark-adapted intensity, c is a constant, and P is the fraction of bleached photopigment |
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How do we test light adaptation?
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Show a person a spot of light on a background of light at slightly different intensity. Find threshold at this given background intensity. Record difference between spot and background = "Just Noticeable Difference". Increase background and repeat measurement.
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Weber's Law and the DeVries-Rose Law deal with what?
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The light adaptation curve
DeVries-Rose predicts that the background is so dim that fluctuations inherent in the light source that produces it play a primary role in determining threshold (delta(I) = Ib^1/2) - slope of light adaptation curve at this point is 1/2 Weber's says that as background brightness increases, increment intensity must be increased so that ratio of increment intensity (delta(I) ) to background intensity (Ib) remains constant delta (I) / Ib = Weber's constant E.g. if delta(I) is 0.14 and the background is increased by 1000 units, delta(I) will have to increase to 140 units to remain visible |
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Only about ____% of rods are bleached at rod saturation.
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10%
*Bleaching of rhodopsin = closure Na+ channels in outer segment = reduced flow of Na+ into outer segment = rod hyperpolarization Only 10% of rhodopsin molecules need to be bleached for all Na+ channels to effectively close |
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When the slope of the light adaptation curve is 1, which law is being followed?
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Weber's
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What does Fechner's log law assume?
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Weber's holds true above threshold values
E.g. if JND intensity is increased by 5X, it would appear 5X brighter S = c(logI) S is brightness, I is stimulus intensity, c is related to Weber's constant This DOES NOT match w/ experimental evidence |
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Steven's Power Law
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Weber's does not hold above threshold
Above threshold, sensation scales as a power law w/ stimulus intensity rather than logarithemically S = (I^alpa)k' where S is sensation magnitude, I is stimulus intensity, alpha is scaling component, k' is a constant This accurately describes suprathreshold sensation's relationship to stimulus intensity, not Fechner's log law |
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Spatial summation is higher in scotopic or photopic vision?
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Scotopic
Explains higher sensitivity and lower acuity associated w/ scotopic VA Larger area of "pixels" are detected at the expense of resolution Biological basis is many rods communicating w/ 1 ganglion cell |
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Ricco's law (in term of spatial summation)
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The number of quanta in a sub-threshold stimulus is constant
IA = C I.e. there is a minimum spot diameter below which the threshold intensity is constant - everything smaller than this is summed together during spatial summation |
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Bloch's Law (temporal summation)
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There is some duration below which everything is added together in temporal summation.
It = C where I is stimulus intensity and t is stimulus duration LIKE RICCO'S LAW (spatial summation) BUT FOR TIME! The scotopic system has a longer critical duration AND a larger critical area than the photopic system. |
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T/F: rods are affected by the Stiles-Crawford effect
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F
Angle at which light strikes cones strongly affects perception of light. Does not occur in rod-dominated vision. |
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Pigments and maximum absorption wavelengths of:
S-cones M-cones L-cones Rods |
S-cones - cyanolabe, 440nm
M-cones - chlorolabe, 534nm L-cones - erythrolabe, 564nm Rods - rhodopsin, 489nm |
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Young's trichromatic theory
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Color information is coded by 3 cone types, and relative activities of different cone types determine the perceived color.
Makes more sense than theory that each color has it's own cone (not enough space for all these neurons) |
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T/F: different wavelengths can be made to appear the same color by manipulating intensity
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T
This is the basis for lack of color-discrimination in monochromacy Monochromatic patients are not able to distinguish colors based on wavelength Monochromatic patients may use BRIGHTNESS to discriminate colors |
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T/F: A dicromatic person is able to adjust brightness of green light and red light until they appear indistinguishable
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F
Dichromatic individuals are able to distinguish colors solely based on wavelength. In order to make two patches of light indistinguishable, a THIRD wavelength needs to be mixed with one of the others. Dichromatic individuals can distinguish color based on wavelength, but this discrimination is limited. Despite a physical wavelength-difference between the patches of light, they can be made to appear similar. This is the concept of METAMERS. |
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T/F: a trichromatic person can adjust the relative intensities of two patches of light until they appear equal, given 4 wavelengths.
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T
Patches will appear identical when they result in the same number of quantal absorptions by each of the three photopigments |
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T/F: the chromophore is identical for all cone photopigments, and the opsin differs.
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T
The chromophore is RETINAL (an aldehyde derivative of retinol / Vit A. Opsin is a virtually-inert chain of AA's interlaced into disc membranes of outer segment M and L cones have opsin gene on X chromosome --> BASIS FOR X-LINKED COLOR VISION DEFICIENCY S cone is on chromosome 3 Rhodopsin is on chromosome 7 |
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Which is most-closely associated w/ wavelength?
Hue Saturation Brightness |
Hue
-This is layperson's "color" - Physical dimension is wavelength and intensity ________________ Saturation -Fullness or purity of color -Wavelength and colorimetric / excitation purity Brightness is brightness! Physical dimension is radiance (watts/steradian/sq m) |
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Nagel anomaloscope distinguishes between dichromacy and anomalous trichromacy. How?
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Dichromats will adjust the test stimulus, anomalous trichomats will adjust the mixture.
________________________________________ Patient shown half-circle 590nm test stimulus and the other half is mixture of two wavelengths on color confusion line for deuteranopes and protanopes. Patient asked to adjust half-circles so they appear equal. Setting 0 for the mixture corresponds to only 546nm light, 73 to only 670nm light. Setting 0 for the test is pale yellow, setting 80-something is bright yellow. NORMAL - mixture scale around 45 and test scale around 17 Protanope - will perceive a match with any test setting when the mixture is set to 0 or to 73 (all fall on confusion line). 670 nm stimulus will be DIM so protanope will SET TEST TO HIGHER SETTING to match stimululus if mixture is set to 0. Protanomalous trichomat - will adjust mix to HIGHER-THAN-NORMAL range since "red-weak" and must add more 670nm than a normal person Deuternope is similar to protanope but does no perceive dimming. Will see match with test at 17 like normal. Deuteranomalous trichomat - will adjust mixture to LOWER THAN NORMAL range since "green-weak" and must add more 546nm than a normal person |
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Protanopes and deuteranopes have poor color discrimination above _____, and tritanopes at _____.
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P & D - above 540nm
T - at 495nm |
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Color vision anomalies:
Protanope Deuteranope Tritanope Protanomalous trichromat Deuternomalous trichomat |
Protanope - dichromat missing erythrolabe. Confuses red, green, yellow, orange. Sees red as DIM, and colors mixed w/ red as only the other base color (e.g. purple looks blue)
Deuteranope - dichromat missing chlorolabe; like protanope but no noticeable dimming of reds to gray Tritanope - dichromat missing cyanolabe; confuses yellow & blue Protanomalous trichromat - erythrolabe spectrum shifted to lower wavelengths; red, orange, green, yellow look similar and all look GREENER; reds may be dimmer; "red weakness" Deuteranomalous trichromat - chlorolabe spectrum is shifted to HIGHER wavelengths; orange, red, yellow green all look similar and MORE RED than to a normal person; "green weakness" |
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Kollner's rule of acquired color defects
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Rough guide saying that"
OUTER RETINAL DISEASE usu leads to B/Y defects INNER RETINAL, ON, and/or VISUAL P'WAY problems lead to R/G defects. |
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Contrast equation
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Contrast = (Lmax - Lavg) / Lavg
where L is luminance |
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A spatial modulation transfer function takes contrast of a grating image / contrast of the object and plots against grating frequency. The SMTF in humans is known as the _______.
High- and low-cutoffs are due to what? |
Contrast sensitivity function
High-frequency cut-off: Optical limitations of the eye (aberrations) PR density is finite Low-f cut-offs: Retinal lateral inhibition (of bipolar cells) RGC center-surround organization (low-freq stimulus elicits effects of inhibitory surround) |
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Converting from cycles/degree frequency from CSF to Snellen VA?
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Divide cycles/degree by 30 to get Snellen in reduced form
E.g. 15 cycles/degree 15/30 = 1/2 --> 20/40 Snellen |
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Mach bands suggest the visual system is acting like what mathematical analyzer?
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Fourier analyzer
Strip w/ gradual increase in luminance as a function of position (light on one end, dark on the the other) will seem to have two bands (Mach bands) at the junction of the transition, one light and one dark. Gradual change in luminance on the band is very low-f, so it is hard to perceive. High-f's look enhanced, resulting in the appearance of obvious boundaries. |
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T/F: motion parallax is a monocular clue to depth.
Depth perception occurs in what imaginary anatomical area? |
T
Panum's fusional area |
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Motion perception:
B-movement Phi-movement |
Spatially-separated lights appear to move forward when flashed sequentially; this is a simple FIRST-ORDER stimulus for motion
B-movement - time between lights is chosen such that the spot appears to move Phi movement - time is just a bit too long, giving partial movement illusion |
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T/F: the parvo p'way detects motion
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F
The MAGNO p'way is mostly responsible for motion perception. Part of V5 (middle temporal area / MT) |
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Purkinje Tree and Troxler Phenomenon deal with what aspect of visual perception?
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Temporal perception
Purkinje Tree - we see retinal blood vessels when we wiggle light on closed eyelid since the light gives higher-temporal-frequency changes to the images on the retina Troxler phenomenon - low-temporal-frequency stimuli disappear from our vision (are ignored) (e.g. retinal BV's under normal conditions) |
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What determines the upper limit of temporal frequency for our visual system?
What is the Ferry-Porter Law? |
Neurons take a finite time to respond to stimuli
CFF (high frequency) scales linearly with log of retinal illumination --> brighter background = higher CFF (likely bc biophysical activity underlying retinal behavior speeds up following increased light adaptation) |
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Other temporal visual effects:
Granit-Harper law Broca-Sulzer effect Brucke-Bartley effect Talbot-Plateau law |
Granit-Harper - CFF increases as stimulus area is increased (peripheral retina better than central at detecting flicker)
Broca-Sulzer - light flashes above threshold appear brightest when they last 50-100 sec Brucke-Bartley - flickering light appears brighter than steady light of same average luminance Talbot-Plateau - flicker greater than CFF (fused stimulus) is perceived as equally bright as non-flickering stimulus with luminance of time-averaged flickering stimulus |
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2BU measurement on von Grafe indicates what?
Base ____ measures an exo, base ____ corrects. Base ____ measure an eso, base ____ corrects. |
Hypophoria
BO measure exo, BI corrects exo *Correction moves the image to the turned fovea* BI measures eso, BO corrects eso |
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2BU measurement on von Grafe indicates what?
Base ____ measures an exo, base ____ corrects. Base ____ measure an eso, base ____ corrects. |
Hypophoria (think BD measures hyperphoria, BU corrects)
BO measure exo, BI corrects exo *Correction moves the image to the turned fovea* BI measures eso, BO corrects eso |
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T/F: A patient with harmonious ARC will show fusion and a tropia
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T
Subjective tests seems normal but objective test reveals tropia |
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T/F: a patient w/ unharmonious ARC will show diplopia and a subjective angle of deviation smaller than the objective angle
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T
ARC occurred but not enough to fully-correct deviation W4D will show 5 dots, Bagolini will show V or /\ |
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T/F: visuoscopy is done binocularly
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F
Tests for monocularly-eccentric fixation! |
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T/F: A patient with harmonious ARC will show normal stereopsis on RD2
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F
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An esotropic patient will report two lines crossing (above/below) two lights on Bagolini testing.
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Below
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