BV Flashcards
What 4 things must you have for normal binocular vision?
equal ocular images
bifoveal fixation
motor fusion
sensory fusion
BI prism causes __vergence which is associated with NFV/PFV?
divergence
NFV
BO prism causes __vergence which is associated with NFV/PFV?
convergence
PFV
Non strabismus (phoria) is a type of ocular deviation which is only present if ______ ______ is disrupted; _______ ________ is present under normal seeing conditions
sensory fusion
bifoveal fixation
What are the 5 characteristics of the cover tests? (things to consider/record)
Direction Magnitude Speed of recovery from dissociation Comitancy Zone of functional binocular vision
What 5 things need to be assessed and managed with an ocular devation?
frequency magnitude direction laterality comitancy
If eso increases at near then the AC/A ratio is considered?
above average
if exo increases at near by ~3 prism dioptres then the AC/A is considered?
normal
If exo increases at near by»_space;>3 prism dioptres then the AC/A is considered
below average
The unilateral cover test is the only way to determine whether a deviation is?
manifest
Alternating cover test reveals what sort of devations and allows measurement of what??
latent deviations
magnitude
Measuring a deviation with each eye fixating independently (ie measuring primary and secondary deviation) helps identify what kind of strabismus?
paretic strabismus
primary deviation = non-strabismic eye fixating
There are two subtypes of calculated AC/A which are?
calculated stimulus AC/A
calculated response AC/A
Calculated stimulus AC/A assumes what?
accurate accommodative response to target ie no lag or lead
For calculated response AC/A, what do you need to do?
measure accommodative response as significant lead or lag will alter AC/A ratio
Do a calculated AC/A for someone with distance phoria 5 exoP, near phoria 5 esoP with 60mm PD.
Stimulus to accommodation at distance = 0
Stimulus to accommodation at near = 2.5 (40cm)
Stimulus to convergence at distance = 0 prism D
Stimulus to convergence at near = 15 prism D (60/40 x 10) = 15 prism D
Amount of vergence response:
The demand is 15 prism D but have to overcome 5 exoP in distance and also overconverges 5 prism D at near so = 25 prism D
Therefore AC/A = 25/2.5 = 10/1
Gradient AC/A equation =
(deviation with lens - original deviation) / power of lens
Strabismus definition
a type of ocular deviation in which bifoveal fixation is not present under normal seeing conditions
The magnitude of a strabismus which is 4 degrees is equivalent to how many prism dioptres?
7
What are the three main causes incomitancies?
paresis of EOM (trauma, surgery)
cranial nerve palsy (III, IV, VI)
syndrome (Brown’s Tendon Sheath, Duane’s Retraction)
Thorington technique, Lancaster screen and Hess-Lancaster screen are used to evaluate what?
incomitancies due to EOM paresis by assessing eye position in different gaze directions
The primary action of the medial rectus is
adduction
The tertiary action of inferior and superior rectus are?
adduction
The superior obliques primary action is?
incycloduction
A 6th nerve palsy affects which EOM?
lateral rectus
A 4th nerve palsy affects which EOM?
superior oblique
Definition of Suppression
The lack of perception of normally visible objects in all or part of the field of vision of one eye occurring under binocular viewing conditions and attributed to cortical inhibition
What is a clinical test for suppression?
Any of the following: Worth 4 light Mallet unit Bagolini lens Sbiza bar
What is the clinical sign of suppression
No stereopsis
Definition of eccentric fixation
Fixation not employing the central foveal area under monocular conditions
Clinical tests for eccentric fixation
Any of the following:
Visuoscopy
Monocular corneal reflex test
Clinical signs of eccentric fixation
reduced VA in affected eye
strabismus
ARC
Normal retinal correspondence
Angle A = 0
Angle H = Angle S = 0
Anomalous retinal correspondence
Angle A ≠ 0
Angle H ≠ Angle S
Harmonius anomalous retinal correspondence (HARC)
H = A
S = 0
History of strab but no surgery
Unharmonius anomalous retinal correspondence (unHARC)
H ≠ A
S ≠ 0
Px with Hx strab and eye surgery
Typical unHARC
Angle H and S have same sign
H > S
Point ‘a’ between fovea (f) and area of regard (p)
Paradoxical type 1 (atypical unHARC)
Angle H and S have opposite sign
A > H
Point ‘p’ between ‘f’ and ‘a’
Px with partially corrected deviation with surgery
Paradoxical type 2 (atypical unHARC)
Angle H and S same sign
H and A opposite sign
S > H
f between a and p
Covariance
intermittent ARC
A = eye deviation
S = 0
Define Angle A
The angle of anomaly - the angle between the anatomical fovea and the pseudo-fovea (point a)
Define Angle H
The objective angle of strabismus - the angle between the fovea and the object of regard
Define Angle S
The subjective angle of strabismus - the angle between the pseudo-fovea and the object of regard
What 4 questions are important to ask during Hx of a strabismic child?
Age of onset
Constant or intermittent
Unilateral or alternating
Torticollis or diploplia?
What are the aims of strabismus management?
- Maintain/restore optimal VAs BE
- Maintain/restore BSV
- Detect any serious pathology or ocular disease
- Achieve cosmetically satisfactory alignment of eyes
- Correct abnormal head posture
What is Essential Infantile Esotropia (EIE)?
EsoT present before 6 months of age which is acquired in early life and is NOT eliminated by correction of hyperopia
What is Dissociated vertical deviation (DVD)?
Vertical anomaly which occurs when eye is deprived of light.
Eye elevates and extorts when amount of light entering is reduced and returns to original position when cover removed.
What is Manifest-latent Nystagmus (MLN)?
nystagmus that is worse when the eye is covered
Adv and disadv of early surgery to correct infantile esoT?
adv - better potential for binocularity due to reduced muscle contraction
disadv - may increase risk of ambly, difficulty in obtaining accurate measurements
Adv and disadv of late surgery to correct infantile esoT?
adv - ambly management easier, more reliable measures
disadv - reduced potential for development of BSV
What three conditions do you not want to do strabismus operation on?
fully accommodative esoT
variable angle of deviation
large angles unlikely to obtain BSV
What is the definition of amblyopia?
reduced BCVA in the absence of ocular pathology and in the presence of an amblyogenic risk factor
Signs of amblyopia (5)
reduced VA increased sensitivity to effects of contour interaction unsteady and unstable fixation reduced contrast sensitivity inaccurate accommodation
DDx of amblyopia (4)
brain tumour affecting visual pathway
retinal disease
optic nerve disease
malingering
Risk factors for amblyopia
- infants born premature, small for gestational age or have first degree relative with ambly
- children with neuro-developmental delay
- infants who experience form deprivation
- ametropia, anisometropia, isometropia
Patching for treatment of amblyopia should be considered only after?
amblyogenic factor removed and adaptation to refractive correction occured
What are the methods of penalisation for Tx of ambly?
Patching
Bangerter filters
Pharmacological penalisation
Define ocular image
the final perceptual cortical image of the retinal image
Define heterophoria
neuromuscular bias that determines the position of the eyes when no stimulus to fusion is present
Define fixation disparity
residual misalignment of foveae within Panum’s fusional area that remains after vergence system compensates for neuromuscular bias
Fixation disparity is also known as _____ _____ and is usually measured clinically with?
associated phoria
prisms and mallet unit
When measuring fusional vergence reserves: What does the blur point represent?
limit of convergence/accommodation relationship
When measuring fusional vergence reserves: What the break point represent?
limit of fusional vergence
What is the difference between calculated and gradient AC/A ratio?
with calculated AC/A ratio the stimulus to accommodation is changed by changing the working distance whereas in gradient AC/A it is changed by placing plus/minus lenses in front of the Rx
What 3 techniques can you use to evaluate incomitancies due to EOM paresis?
- assessing eye position in different gaze direction
- cover test (Park’s three step)
- Broad H test
Give the three muscle sequelae after EOM paresis using example of paresis of RLR
- Overaction of contralateral synergist = LMR
- Overaction of ipsilateral antagonist = RMR
- Secondary underaction of contralateral antagonist
What is the one object method for measuring pathological diplopia
Thorington technique with maddox rod
What are the two object methods for measuring pathological diplopia (3)
- anaglyphic (Hess-Lancaster Test)
- Brewster stereoscope
- Wheatstone stereoscope
Do Park’s Three Step Test for the following on refill:
- Right hypertropia, worse on laevo-version and left head tilt
LSR is the paretic muscle
Do Park’s Three Step Test for the following on refill:
- Right hypertropia worse on dextro-version and right head tilt
LIO is the paretic muscle
Do Park’s Three Step Test for the following on refill:
- Left hypertropia worse on laevo-version and left head tilt
RIO is the paretic muscle
Define aniseikonia
a relative difference in the size and/or shape of the ocular images
What is acquired optical aniseikonia?
aniseikonia due to refractive lenses worn creating a difference in ocular image size
If antisometropia is 100% refractive then what should be used?
isogonal lenses or CLs
If antisometropia is 100% axial then what should be used?
spectacles designed for specific vertex distance
What is axial anisometropia?
axial anisometropia is a significant difference in refractive errors of the two eyes due to the difference in axial lengths
What is the relationship between axial anisometropia and aniseikonia?
aniseikonia is present whether or not axial anisometropia is corrected or left uncorrected
How can you substantially reduce aniseikonia due to axial anisometropia?
EBT lenses (equal base curve and thickness) placed at the appropriate vertex distance
What is refractive anisometropia?
it is a significant difference in refractive errors of the two eyes due to the difference in corneal curvature and/or physiological lens power
What is the main difference between axial anisometropia and refractive anisometropia in terms of aniseikonia?
refractive anisometropia does not produce aniseikonia uncorrected
What is meridional aniseikonia?
aniseikonia in which there is a symmetrical merdional difference between the size of the ocular images of the two eyes, so that the ocular image in one meridian is larger or smaller than the corresponding meridian of the other eye
What is anatomical aniseikonia?
aniseikonia due to an anatomical cause, such as unequal distribution of the retinal elements
Comment on aniseikonia caused by retinally induced aniseikonia (5)
- creates local aniseikonia
- static aniseikonia is unrelated to dynamic aniseikonia
- occasionally paradoxical aniseikonia
- often need different lens designs for static and dynamic vision
- classical lens design doesn’t often solve problem (occlusion usually best)
What is local aniseikonia?
type of aniseikonia which is dependent on retinal location
Sensory aniseikonia is also known as
static aniseikonia
motor aniseikonia is also known as
dynamic aniseikonia
Symptoms of aniseikonia are only produced if?
if the sensory fusion mechanisms are active
What sort of symptoms can someone with aniseikonia present with?
- HAs
- asthenopia
- photophobia
- diplopia/confusion
- reading difficulties
- nausea
- general fatigue and nervousness
- space distortions
Paediatric early onset aniseikonia can cause ____ _____ which can cause what?
unilateral suppression
amblyopia
Paediatric late onset aniseikonia usually produces ____ because the cortical image in one eye is not suppressed and the aniseikonia precludes binocular fusion
diplopia
What are the three major causes for amblyopia?
- anisometropia producing suppression
- strabismus producing suppression
- monocular and/or binocular form deprivation
What is a method for measuring the stereoscopic spatial distortion (aniseikonia)?
Remole Eikonometer - Px looks through eikonometer which has many rods. Rods are adjusted until they give the perception that they are all in the same plane
Dynamic aniseikonia can be measured using what technique?
Robertson technique
How much % of aniseikonia should you correct for someone with dynamic aniseikonia?
2/3
Assign the correct sign (+/-) for the following directions:
- Right hyper
- Left hypo
- Right hypo
- Left hyper
- +
- +
- -
- -
Why must we gradually increase the stimulus to vergence when measuring PFV and NFV?
Gradually increasing the retinal disparity provides a ramp stimulus
Why must we record the first sustained blur instead of first perceived blur?
Because this is the point at which the vergence and accommodation systems are not able to make up for the vergence demand
How do we measure the vergence and accommodative responses to a step stimulus (how do we measure voluntary vergence - vergence accommodation)? (3)
- Recovery on unilateral cover test
- Recovery on NPC
- Recovery when large prism amounts are introduced before the eyes
Sheard’s criterion is used for what sort of phoria and states?
exophorias
reserve must be at least twice the demand
Percival’s criterion is used for what sort of deviations and states? (3)
eso deviations
the greater reserve must not be more than twice the lesser opposing reserve OR the demand point for the testing distance should fall within the middle third of the motor fusion range
Define sensory fusion
the process by which stimuli is seen separately by the two eyes are combined into a single percept. Under normal binocular conditions this occurs when the same object stimulates corresponding retinal areas
Describe tests used to assess sensory fusion
- Grade 1 sensory fusion - stereoscope or maddox rod + penlight technique - superimposition
- Grade 2 sensory fusion - Suppression monitors - one percept from two similar images
- Grade 3 sensory fusion - Titmus fly test - depth perception
Describe the SILO effect
Smaller In Larger Out.
Smaller percept when eyes are turned in as with base out prisms and larger percept when eyes are turned out as with base in prisms.
Occurs due to retinal image size constancy - as you diverge you expect the retinal image size to get smaller but because it is not changing it appears to become larger and move further away
Describe suppression
the lack or inability of perception of normally visible objects in all or part of the field of vision of one eye, occurring only on simultaneous stimulation of both eyes and attributed to cortical inhibition
How is the 4 prism dioptre test useful in assessing binocular vision?
Tests for suppression scotoma
- eye with BO prism in front of it should adduct 4 prism dioptres
- eye without prism should come back to the same position
What 6 aspects of accommodation should be tested in an accommodative work-up?
- equal stimuli to accommodation
- AC/A ratios
- AOA - monocular and binocular
- Accuracy (lag/lead)
- Accommodative facility
- Sustained accommodation (fatigue)
How do you test equal stimuli to accommodation for distance and near?
distance - binocular refraction and balancing technique
near - NV-100 (Mallet box) or dynamic ret
Px has: - PD of 6cm - Dist 5 exoP - Near 5 esoP What is the calculated AC/A?
10 prism dioptres/1D
Px: - 6cm PD - Dist 12 exoP - AC/A = 12/1 What is the Pxs near deviation?
3 esoP
12 x 2.5 (STA) = 30
30-12-15 = 3 eso
Px: - Gradient AC/A = 8/1 - Near 12 esoP - WD = 40cm What is the ocular deviation through reading addition of +1.00, +2.00 and through maximum reading addition?
+1.00 = 4 esoP
+2.00 = 4 exoP
max reading = +2.50 = 8 exoP
Px: - PD 6cm - Dist 5 exoP - Near 5 esoP - Accommodative lag = 1.00D Work out calculated and response AC/A
Calculated AC/A = 10/1
Response AC/A = 16.7 prism dioptres/1D
(STA - lag = 2.5 - 1 = 1.5 –> STC/STA = 25/1.5 = 16.7/1)
PD 6cm Dist 5 exoP Near 15 exoP Accommodative lag = 1.00D Work out calculated and response AC/A
Calculated = 2 prism D/1D Response = 5/1.5 = 3.33 prism dioptres/1D
What are the two methods of measuring monocular AOA?
- push-up technique with near target
2. Sheard’s technique (minus lens technique) - minus lenses introduced until sustained blur
Why may the push-up technique be difficult for paediatric patients and how can you adapt this technique for them?
Children may find it difficult to judge when the target becomes blurry.
Push the target in to where you know it will be blurry and pull it away. The distance at which the child can first identify the letter is assumed to give the AOA
A binocular AOA that is lower than the monocular counterpart observed with the push-up technique is indicative of?
a vergence problem
Which method is not appropriate for measuring binocular AOA and why?
Sheard’s technique because when done binocularly the result is affected by vergence
how can sustained accommodation (fatigue) be observed?
accommodative facility that is initially normal but reduces over time
What are three sensory adaptations to strabismus?
Suppression
Eccentric fixation
Anomalous retinal correspondence
The monocular corneal reflex test is a method of testing what? Describe this test
Eccentric fixation
- Penlight at 50cm
- Compare location of corneal reflex of the ‘normal’ eye with suspected eye
- Record the angle in mm from centre of pupil (1mm = 22 prism dioptres)
Define ARC
A binocular condition where the fovea of one eye has the same directional value as an afoveal point of the other eye
Describe the Hering-Bielschowsky After Image Test
- flash one eye with thin vertical light (with middle portion missing) and the other with a horizontal light (same as vertical).
- Px gets an after image for each eye and the perception of the images which is reported tells us about their retinal correspondence
Name 3 signs of divergence insufficiency
- Low NFV at distance (key clinical sign)
- esoP greater at distance
- low AC/A ratio
DDx for divergence insufficiency (4)
- 6th nerve palsy/paresis
- convergence excess
- basic esophoria
- divergence paralysis
Give three symptoms of divergence insufficiency
- intermittent double vision at distance
- diplopia worsens if tired
- H/As
- asthenopia
- blurred vision
- sensitivity to light
- motion sickness
- nausea
Tx of divergence insufficiency (3) and describe
1) correction of ametropia
- rarely any effect on angle of deviation
- Prescribe maximum plus to reduce deviation)
2) Prism
- correct vertical deviations.
- Horizontal prism most effective Tx approach - Prescribe based on minimum amount that relieves fixation disparity (BO relieving prism for full time dist wear)
3) Vision therapy
Goals are:
- improve NFV (start close and gradually move out further)
- develop feeling of diverging
- normalise accommodative amplitudes/facility (if any abnormality)
- Final step is to normalise distance NFV
Infantile esotropia age of onset and signs (5 signs)
2-4 months
- large angle constant deviation (40-60PD)
- may have cross fixation
- low to moderate hyperopia
- amblyopia
- latent/manifest nystagmus
signs of accommodative esotropia (age of onset 1-7 yo w/ average 2.5 years) 3 marks
- may be fully or partially accommodative
- angle 10-35PD, rarely >40
- AC/A ratio dictates difference between distance and near angles
Aetiology of fully refractive accommodative esotropia
uncorrected hyperopia
management of fully refractive accommodative esotropia (2 ish)
- full hyperopic correction - relaxes accommodation and fully corrects esotropia
- no surgery
aetiology of partially refractive accommodative esotropia
partial accommodative element with superimposed basal deviation
management of partially refractive accommodative esotropia (3)
- full hyperopic correction - relaxes accommodation and reduces esoT
- measure remaining esoT and correct with relieving BO prisms (prisms can be split or put in non-dominant eye)
- surgery if necessary (optical correction still needed afterwards)
Comment on the characteristics of convergence excess in terms of deviation, AC/A ratio, PFV/NFV, stereopsis, AOA, facility, dynamic ret, BMA/BPA, suppression (9)
- eso deviation
- insignificant eso deviation at distance
- significant eso deviation at near - there is usually an over-convergence resulting in an esotropia when viewing a point closer than the NPC - Stimulus calculated AC/A ratio is higher than normal and response calculated AC/A is even higher
- PFV at near is often excessive and if NFV is present it is insufficient to meet Percival’s criterion (due to excessive PFV)
- Stereopsis - inside NPC stereopsis is absent. Outside the NPC the threshold of stereopsis is generally good
- Decreased BMA due to reduced NFV reserves
- Suppression
- if suppression exists - usually intermittent
- if suppression absent - diplopia and esoT is intermittent
- if suppression intermittent - esotropia is intermittent - High MEM
- Normal AOA
- Fails to clear minus on binocular facility
Symptoms of convergence excess (3 main with specific symptoms)
- visual discomfort
- ocular fatigue
- H/As
- asthenopia - Unstable vergence/accommodation system
- intermittent blur at near
- diplopia at near
- squinting - no desire to do work
- affects academic performance
- affects productivity in workforce
Aetiology of convergence excess (3)
- Hereditary
- inheritance factor with large eso deviation - Sensory factors
- any disruption with sensory integration will reduce measurements of NFV leading to CE - Motor factors
- high stimulus and response calculated AC/A ratio may be assoc with hyperopia and/or basal deviation
- excessive PFV
Management of convergence excess (4)
- full hyperopic correction
- relieving prisms for residual esotropia at distance
- plus addition for residual esotropia at near
- usually no surgery necessary (bifocal correction needed afterwards if done)
Prognosis of CE
- hyperopia left uncorrected - esoT may become constant and lead to ambly
- later Tx –> poorer prog
DDx of CE (4)
- basic esoP
- divergence insufficiency
- accommodative spasm assoc with inflam/drugs
- accommodative disorders
Vision therapy goals for CE
- normalise NFV amplitudes
- develop voluntary convergence/divergence
- normalise accommodative amplitude/facility
When should vision therapy for CE be considered? (3)
where NFV very low, large esoP and symptomatic after spectacle wear
