amblyopia\ Flashcards
Amblyopia Definition
NOT - Congenital
Any condition that causes the brain to receive images of poor or unequal quality from the two eyes for an extended period, can lead to suppression of the poor image
Developmental anomaly of spatial vision that is present early in life and is almost always associated with strabismus, anisometropia or both
AMBLYOPIA
Optometry - why do we care?
Affect us day to day?
- More vision loss in the <45yo population than ALL other ocular problems combined (excluding refractive error)
- It’s treatable – if detected early enough, we can prevent or reverse the impairment
- Detection, prevention, and treatment in the pediatric population
- Part of the differential diagnosis of VA loss in all ages
Amblyogrnic Risk factors
- Unilateral constant strabismus at both distance and near
- Congenital cataract/ptosis
- High refractive error (aniso / iso)
Amblyopia:
Developmental anomaly:
Visual system is relatively intact at birth connections between the eye and brain need to form as the visual system develop
Both eyes are giving the brain visual information that is equal in clarity, size, quality, and frequency
When amblyopia develops, it leads to anatomical changes to the LGN (parvo), and visualcortex, ultimately, leading to functional changes
Development of Amblyopia
- The weaker eye becomes anatomically and neurologically underrepresented in the visual pathway
- The stronger eye develops more connections to the brain, it outcompetes the weaker eye
- The stronger eye initiates a (-) inhibitory signal (GABA) to further knock down and suppress the weaker eye
Structural Abnormalities Amblyopia
LGN
Visual cortex (ocular dominance collumns)
3 major stops in the visual pathway:
o (1) Retina normal – (2) LGN (Parvo cells = smaller for central fine vision / Magno cells = larger for peripheral vision) – (3) visual cortex
- shrunken layers of LGN supplied by amblyopiceye
- shrunken and fewer PARVO cells, but normal magno cells
- loss of binocular cells found in ocular dominance columns in form-deprived kittens
- Shift in ocular dominance columns in extra-striate & higher processing areas
- This impacts attention and decision making and can also impact reading
Amblyopia:
Spatial Vision problem
Amblyopes = problem with the PARVOcellular pathway
o Use the periphery (MAGNO pathway) as a model of what an amblyope sees
o Amblyopes can see in dim, stationary, and low spatial frequency settings,
CAN’T SEE
trouble in bright, colorful, high spatial frequency settings
Amblyopia
Visual Acuity
Hallmark sign of AMBLYOPIA
Amblyopes, there is a wide range of deficits across a wide range of acuities
“Hill of vision”
May get some letters, reverse some, miss some, but never really get all of them right even if they are above the threshold
Threshold acuity alone is not the best way to measure acuity, use logMAR chart with the letter by letter count
More accurate, credit can be given for improvement as the VA normalizes into a pattern more similar to non-amblyopes
Whole chart > Isolated line > Isolated letter
Abnormal Monocular fixation
- Eccentric fixation
- Fixation instability
- Spatial uncertainty
- Sparse spatial sampling
- Spatial distortion
ECCENTRIC FIXATION:
occurs under MONOCULAR* conditions, when the eye uses a point other than the fovea to fixate an object
Rule of thumb: 1-2 lines of decreased acuity can be attributed to 1 prism diopter of EF
Eccentric fixators are UNAWARE they are not using their fovea during monocular fixation
If binocular and NOT using fovea = Abnormal correspondence*
Can explain unilateral decreased VA in an otherwise normal looking eye (ie. monofixation syndrome)
Monocular acuity is decreased in an eye that is not using the fovea for monocular fixation
o The larger the magnitude of the eccentric fixation, the greater the resulting decreased Acuity
Amblyopia
Crowding
(Peripheral reading is not affected) MAGNO intact
Reading centrally with amblyopic eye, amblyopes require abnormally large critical spacing, BUT still were able to read all larger spacings at normal rates
Amblyopia:
More than just VA affected:
- Reduced and variable accommodation
- Abnormal eye movements
- Poor spatial judgements
- Reduced depth perception
- Reduced contrast sensitivity
- Reading speed? (even with both eyes open)
- Pupil abnormalities? (Increased latency in central 30 ‘Of vision)
Amblyopia
Reading:
Amblyopes show REDUCED READING SPEED (words per minute) compared to non-amblyopes when letter size is controlled
Differences exist under binocular AND monocular conditions even when tested with the dominant eye (15%) – problem is NOT only with the amblyopic eye
No significant difference with strabismic and anisometropic amblyopia
Amblyopia
Pupilary responces:
There are subtle pupil problems with amblyopes that resemble APDs
- With the OBJECTIVE tests, there was an INCREASED LATENCY of pupil response
- With automated pupil perimetry, the increase in latency was only in the central 30o
Amblyopia
Fixation Instability
Spatial Uncertainty
FIXATIION INSTABILITY:
• You may get much larger movements in amblyopes, movements more consistent with a larger target in normal
o Typically, small target = small movements / large target = large movements
SPATIAL UNCERTAINTY: The ability to judge space
• With the two orange triangles, the task is to state when the lines “line up” with the triangles
• At the visual cortex, more channels helps the patient judge depth, contrast, and spatial localization
Amblyopes have less filters/channels, and the image is more raw/harder to interpret
Amblyopia
Acuity:
Snellen problems
logMAR
Contrast Sensitivity
Problems with Snellen
- More crowding for amblyopes
- Non-uniform progression
- Variable difficulty of letters
- Tests at threshold only
LogMAR Chart
Size, spatial frequency, and level of difficulty is kept consistent throughout the chart
Will start to see improvements on higher lines first THEN acuity threshold will improve
Amblyopia
Acuity Recommendations
Contrast Sensitivity Function
• Amblyopes have the greatest issues with increased spatial frequency and increased contrast (parvo)
Acuity Recommendations
- Refraction, projector chart okay, but understand limits of Snellen
- Diagnostically, whole chart, logMAR is best
Prognostically, isolated letter vs whole chart
- Large difference is good indicator
- Single letter VA is expected post therapy
- o Stop Tx as gap closes
Amblyopia
Key point summary:
- Vision loss is CORTICAL
- Resembles peripheral vision MAGNO
- Dominant eye also show functional defects
-
CRITICAL PERIOD - When eye is susceptable to amblyogenic factors
- Begins at birth, maximum at 6-9months, slowly declines until approximately 8yrs
- Cant develop but still able to treat.
-
Potential GABA antagonists (GABA mediates suppression)
inhibit GABA, keep the critical period open longer
Depth of Amblyopia:
o Note: Amblyopia that appeared earlier is harder to treat and more severe
Deep vs superficial amblyopia
§ Type of insult
§ Timing of insult
• Earlier on and later diagnosis, more severe and harder to treat
§ Treatment (time initiated, type of Tx, compliance)
Types of Amblyopia:
3 Main
+ Other 3
Functional Amblyopia
- Strabismic amblyopia (Unilateral constant strabismus at D/N)
- Refractive amblyopia (Anisometropic vs Isometropic)
- Form deprivation amblyopia (Unilateral or bilateral)
Other Amblyopias (nothing interfering with the visual pathway, not “true” amblyopia)
- “Organic”amblyopia
- Hysteric alamblyopia ( Tunnel fields) Younge female Px’s
- Idiopathic amblyopia
Amblyopia
diagnosis of exclusion and inclusion
Exclusion:
Rule out ocular pathology as a cause of the decreased acuity by at least performing thorough internal and external health evaluation with DFE
Inclusion:
For any amblyogenic risk factors
Functional Amblyopia
STRABISMIC AMBLYOPIA:
Constant unilateral strabismus at distance and near with an onset before7yo
VA
Why and how does it result:
VA : 20/40 - 20/100, but can be worse
- CAN’T be CF (counting fingers) or LP (light perception)
- never binocular - this creates an advantage/disadvantage situation
- earlier = the more amblyogenic it will be because fewer connections will form in the brain
CONFUSION: Fovea of strabismic eye is stimulated by a different object than the object of fixation
DIPLOPIA: An object of fixation falls on the fovea of one eye and non foveal point of the other eye
Suppression = Response to eliminate confusion or diplopia
suppression zone larger in exotropes because exotropia tends to be larger in magnitude than esotropia
What type of strab causes Amlyopia:
Onset
Intermittent /Constant
Alt / Unilateral
Magnitude
Direction
Age of onset = with in the critical period
Constant at Dist and Near (even 5% fixation Intermittent)
Unilateral - amblyopia if alternating possible - Only if a strong preference for 1 eye (5%) would be less Amblyopic
Magnitude - higher magnitude NOT more amblyogenic
Direction - Does not matter /
EXO’s more intermittent
_ESO’s tend to be constan_t, likely to develop amblyopia
unilateral strabismus to alternating strabismus - Considered an improvement
Amblyopia
ESO vs EXO
ESOtropia
- 9x more likely to lead to an IOD (intraocular acuity difference) of ≥ 2 lines
- leads to ↓ VA (constant)
Exotropia
- Intermittent early in life not amblyogenic
SENSORY STRABISMUS: Decreased acuity in one eye so the eye naturally drifts EXO out
- Retinal pathology
- Toxoplasmosis scar
- macularscar
- retinoblastoma
- congenital cataract
Amblyopia
Refractive
Anisometropia vs Isometropia
Dissimilarity of retinal images due to changes in clarity, size, and contrast
Suppression
ANISOmetropic refractive amblyopia:
- Uncorrected high UNIlateral refractive error that is present early in life, one eyes gets the advantage
- VA = 20/80 or better, milder or more superficial amblyopia than strabismus
- Hyperopic anisometropia, more amblyogenic - because accommodation is symmetrical, more hyperopic eye blurred more at BOTH distance and near
- Myopic anisometropia, each eye has dominance (one at distance,the other at near)
ISOmetropic refractive error
- significant BIlateral refractive error, disrupts overall development, no shifts in ocular dominance columns or changes in the LGN
- VA = 20/30 and 20/70
- Myopia vs hyperopia vs astigmatism
- NO Suppression
Aniso/isoametropia , the magnitude of RE can predict the severity of decreased VA and the depth of amblyopia
AMBLYOGENIC ASTIGMATISM:
unilaterally, bilaterally, isolated or in combination with other refractive errors
(oblique > ATR > WTR)
“meridional amblyopia” if just the astigmatism is causing the amblyopia
- Recognition acuity shows overall decrease E has horizontal and vertical components
- Grating acuity shows a deficit predicted by the axis
- Magnitude and axis determine amblyogenic potential (oblique > ATR > WTR)
Horizontal meridian = vertical image
Vertical meridian = horizontal image
o Ie. plano -4.00 x180, the horizontal axis is clearer, therefore, the vertical image would be clearer
The problem 180 = Vertical Clearer
o Note: meridional and isometropic amblyopia are the mildest forms of amblyopia
Predicted Refractive Amblyopia
There is a strong linear relationship between 1-5D of anisometropia
5D of aniso approaches 100% chance of IOD (intraocular acuity difference) of ≥ 2 lines
With anisometropia:
o >2D of SE aniso →40x more likely to get an IOD & decreased acuity in 1 eye
With isometropia:
o Not as likely to see bilateral decreased VA
o >4D hyperopia in least hyperopic eye →11xmore likely to have bilateral decreased VA
FORM DEPRIVATION AMBLYOPIA:
congenital or very early acquired degradation of visual stimuli
FORM DEPRIVATION AMBLYOPIA
- Congenital or very early acquired degradation of visual stimuli
- Physical obstruction along the visual axis, prevents eye and brain from forming connections
-
Causes:
- Congenital cataracts
- Ptosis
- Corneal opacity
- Complete vs. partial obstruction
- Unilateral vs. bilateral (easier to treatment, simply slower)
- Time of onset: Critical Worse
- Duration of onset
- Lapsed time before treatment
Latrogenic Amblyopia from occlusion treatment (ie. patching all day, don’t
ORGANIC AMBLYOPIA
IDIOPATHIC AMBLYOPIA
HYSTERICAL/PSYCHOGENIC AMBLYOPIA
ORGANIC AMBLYOPIA
- Irreversible by treatment, secondary to not obvious structural changes
- Ex: high myopes with mal-oriented PRs
- toxic amblyopia (lead poisoning)
- nutritional amblyopia (alcohol abuse)
IDIOPATHIC AMBLYOPIA
- decreased vision with no strabismus, significant RE or episode of form deprivation – no amblyogenic factors
- Responds to treatment, but then shows regressio
-
Transient amblyogenic factor?
- Constant strabismus early in life that resolved
- High anisometropia as a kid that emmetropized
HYSTERICAL/PSYCHOGENIC AMBLYOPIA
- VA loss due to an emotional problem
- typically bilateral VA loss 20/70-20/200
- females ~8-14yo
Tubular fields peripheral vision same even when you vary the distance
Malingerers
Expected test results
• Expected response from malingerers
- Color vision – all plates wrong
- 4BO test – normal fusional response, objective
- Retinoscopy – minimal Rx (even cycloplegic), but significant improvement with spectacles
- Cover test – no problem seeing fixation target
- Stereopsis – unpredictable, but VA may improve with polaroid glasses
Diagnosing Amblyopia:
4 Key Points
- Amblyopia is a diagnosis of inclusion and exclusion – rule out ocular disease and document cause of amblyopia
- Label the specific type of amblyopia
- Diagnosis must make sense in severity – the depth (severity of acuity loss) of amblyopia depends on several factors including cause, onset, previous treatment and compliance
- Response to treatment is part of the diagnosis – once treatment is started, amblyopia usually improves and should never get worse
The Exam and expected findings in amblyopia
- VA – near AND distance VA should be equally reduced
- Check binocular VA to compare
- Pinhole expected endpoint with refraction
- Cover test – correct sized target, 2 lines above amblyopic eye
- Stereo – Get baseline to monitor improvement (trying to improve global stereo)
- Fixation status
-
Refractive error – OBJECTIVE retinoscopy for peds
- CYCLO for: full anisometropia and astigmatism
- Cyclorefraction= 2gtt of1 % cyclopentolate separated by 5 min.
Cycloplegic – minimal dilation (only paralysis of accommodation), therefore, used in conjunction with tropicamide
Functionla testing at followm up if RX prescribed
Return Visit after Rx Wear (check compliance of glasses)
and
Subsequent Visits
REPEAT CYCLO FOR ALL RX CHANGES
Return Visit after Rx Wear (check compliance of glasses)
- Ensure compliance with glasses
- LENSOMETRY!
- Repeat VA
- Dry retinoscopy over Rx
- Repeat cover test
-
Repeat stereo
- Local – monocular cues, easier
- Global – requires polaroid spectacles
- Repeat fixation status
Subsequent Visits
- History probing compliance
- Repeat 1-5 to monitor for improvement at every visit
***Repeat cyclo before all Rx changes or if improvement stalls
Amblyopia TX
Goal of treatment: to maximize VA with foveal fixation and consequently maximize binocularity
How?
Why?
Optical correction
Occlusion
evidence-based approach to managing amblyopia
- Prescribe an Rx if necessary.
- Consider patching or some type of occlusion therapy
- Expect improvement every 3 months
Amblyopia: Benifits of treatment
- Functional impact + treatment success rates of 60-70%
- 1.2 to 10x increased lifetime risk of serious vision loss in the fellow eye from disease or injury
o Note: The 5-year cumulative incidence of bilateral visual impairment (BVI – worse than 20/100 in the better seeing eye) is significantly increased in patients with amblyopia compared to non-amblyopes
§ Non-amblyopes become more susceptible to BVI w/ age
Amblyopia treatment option Studies
Patching
Optical correction
Prescribing for Anisometropia
FULL anisometropia
FULL astigmatism
Cut hyperopia EQUALLY but not > 1.5D residual
Patching:
- Full time vs. part time (6 hours) patching for severe amblyopia = No difference in VA
- Part time (6 hours) vs. minimal time (2 hours) patching for moderate amblyopia = No difference in VA
The Optical Correction
- provide clearest retinal image possible in each eye and equalize the RE between the eyes
- cycloplegia: baseline – more reliable findings
- rely on OBJECTIVE testing
Prescribing for Anisometropia
FULL anisometropia
FULL astigmatism
Cut hyperopia EQUALLY but not > 1.5D residual
Glasses be worn before prescribing occlusion + expected improvement
10-12 weeks.. 3 lines in 3 mos
Guidlines for Amblyopia TX
*Regardless of the type of amblyopia, try optical correction alone for at least 3
months, and expect ~3 lines of improvement
Full Correction
-
Glasses be worn before prescribing occlusion and expected improvement.
- 10-12 weeks.. 3 lines in 3 mos
- With glasses alone, patients improved VA by ~2-3 lines on average after 3 mos
- 1/3 of children did not require further treatment intervention
-
Strabismic and strabismic-aniso amblyopes treated with optimal optical correction
- improved 3 lines in 3 months for both groups
- Monitor acuity (every 2-3 months) until there is no significant improvement for at least 2-3 consecutive visits
Patching
- Clinical recommendation: Part time occlusion (in children 3-8yo) of at least 3-4hours/day is as effective as longer amounts of occlusion
- 3-4hours do NOT need to be consecutive
- 2-3 lines of improvement in3month
- Majority of improvement takes place by14weeks
- Compliance ist he major obstacle
Patching / TX
Compiance vs Concordance
Why poor
Note: stress on the family is the largest obstacle to good compliance
Compliance: The extent to which patient behavior matches the prescribers recommendations
Concordance: Agreement that is reached after negotiation between a patient and healthcare provider that respects the beliefs and wishes of the patients in determining whether, when and how medicines are to be taken
Compliance - allow to explain expected outcome = Better treatment
-
Poor compliance
- Parents not understanding treatment/condition
- No improvement
- Social and educational difficulties
- Skin irritation
Note: stress on the family is the largest obstacle to good compliance
Patching Compliance
- Compliance with patching hours was 44%
- Longer treatment times led to worse compliance
- Increased visit frequency led to better compliance
- Weekday compliance better than weekend
IMPROVE
- Educational materials aimed at the parent and child
- Reward Calendar
- Fun Patches
Alternatives to Occlusion:
“Fun” patches
- Bangerter filters to create blur in dominant eye - MODERATE AMBLY
- Pharmacological penalization (use of atropine to blur the dominant eye) effective for mild, moderate, and severe amblyopia
- Occluder contact lens for dense amblyopia
- High plus contact lenses for milder amblyopia
Bangerter Filter
- Sticker different densities on the back of RX
- Scattered blur like a cataract, decrease VA from 20/30- 20/300 depending on filter
- can decrease contrast after acertain point
- NOT the best option if the patient has poor compliance with glasses Study on Bangerter filters compared to conventional patching
*Bangerter filters are a reasonable option to consider for the initial treatment of MODERATE amblyopia
Atropine
- Higher compliance
- First line of treatment along with conventional patching; both are considered equally effective for mild, moderate, and severe amblyopia
- patching and atropine are equally effective
Reduced dosage (2x/week) appears to be as effective as daily atropine
ClinicalRecommendation:
- Rx1gtts,1%atropine ophthalmic solution daily until improvement noted and then reduce schedule
- Follow up 1 week after initiation of atropine and then every 4-6 weeks after that
- careful refraction of better eye 20/20 prevent Iatrogenic Amblyopia
- Recommend hat and sunglasses for outside. Patient’s pupil will be dilated 24/7
Opaque Contact Lenses
- expensive and only reserved for severe amblyopia
- high plus CL in Moderate Amblyopia
- poses a higher risk of infection to good eye
Age of Amblyopia treatment treatment
- younger, moderate amblyopes will have increased likelihood of success, compared to older severe amblyopes
- Children < 4yo responded more rapidly and with smaller doses of patching compared to older children
- 25% of all subjects improved with spectacles ALONE (all ages)
- Patching/atropine was effective in the 7-12 yo group
- Patching was effective in the13-17yo group ONLY if there was no previous treatment (ie. never worn glasses or done patching before)
Amblyopia treatment in Adults
Chemical (Sinemet)
Perceptaul learning (Video games)
The cornerstone of dichoptic training for amblyopia is that it is a binocular disorder resulting from interocular suppression, effective treatment should engage BOTH EYES which may require the penalization of the dominant eye
- Levodopa/Carbidopa (Sinemet® - Merck and Co)
- LEVODOPA: Intermediate in the biosynthesis of dopamine, originally prescribed for Parkinson’s disease
- CARBIDOPA: Peripheral decarboxylase inhibitor and prevents break down of levodopa
- When given together (Sinemet), INCREASE dopamine levels (which can INCREASE plasticity)
Perceptual learning
- Concept that humans are capable of improving performance through practice
- perceptual learning tasks that are specifically aimed at this network should result in improved spatial vision and function
-
increased binocularity and stereo
- Conclusion: 68% of treatment group improved 2 or more lines independent of age
- The biggest gains of acuity were seen in contrast sensitivity tasks
-
Video Game play
- Arousal and reward may increase dopamine levels à increased plasticity of brain
significant improvement in the dichoptic learning, but not the monocular. Binocular huge improvement was seen in VA and stereo
Final treatment Recomendations AMBLYOPIA
1st line patching + atropine and if those plateau, try dichoptic training
- Optical treatment
- 3 lines in 3 months
- 1/3 resolve (milder anisometropic amblyopes with stereo at baseline)
- every 4-6weeks until plateaus for 2-3 app
- Conventional occlusion or atropine penalization (first line Tx)
- 3 lines in 3 months
- every 4-6 weeks until plateaus for 2-3 app
- Conventional occlusion – At least 3-4 hrs/day recommended
- Atropine 1% – Daily or reduced schedule (2x/week) depending on needs of patient (start daily and then reduce
- 1 week f/up
- iatrogenic Amblyopia risk / monitor good eye VA
- Recommend hat and sunglasses
- Compliance
- Educational materials
- More frequent follow-up visits
- Lower doses to start, but consider increasing the non-responders
-
Regression after cessation of occlusion MONITOR
- first 3 months
- 1 year follow up
- Maintenance patching: Regression 4x more likely in children not weaned off of patching
- 3hr for 1 month, 2hr for 1 month, 1hr for1month
Strabismus
Phoria vs Strab
Strabismus:
Manifested deviation from the line of sight – visual axes not aligned when BOTH eyes are open (>1pd)
Phoria is only seen when one eye is covered
Strabismus, whether constant or intermittent, at somepointwhenbotheyesare open, one of the eyes is deviated
Describing Strabismus
- Direction
- Laterality
- Frequency
- D vs N
- Magnitude
- Comitancy
- Version/ductions
Direction
- Esotropia, exotropia, hypertropia, cyclotropia
-
Recording:(vertical)
- Tropia, specify vertical (hypo or hyper) deviation by the tropic eye
- Phoria, specify HYPER deviation
- Torsion – SO = intorsion / IO = extorsion “Inferior people extort money”
Laterality
- Unilateral or alternating (Better prognosis)
Laterality Control
L constant EXOTROPIA example
-
Unilateral strabismus
- Cover OD, stays out, only when OS is covered, OD is forced to fixate and will move in, when uncovered, instantly deviates out
-
Loses before blink (alternator with specific FIXATION PREFERENCE)
- Cover OD, stays out, cover OS, OD is forced to fixate and will move in, when uncovered, will deviate out again within a secon
-
Loses during blink (alternator with specific FIXATION PREFERENCE)
- Cover OD, stays out, cover OS, OD is forced to fixate and will move in, when uncovered, will deviate out again until blink, in this case, strong left fixation preference
-
Loses after blink (alternator with specific FIXATION PREFERENCE)
- Still a left fixation preference, but not as noticeable since it takes more blinks for the OS to recover and OD to become deviated again
-
True alternator
- 50/50 OD, OS
Frequency
Constant or intermittent
Frequency control
ex Unilateral right exo___ ?
-
Phoria
- Cover OD, underneath deviates out, uncover, OD instantly refixates on the target
-
Recovers before blink (intermittent strabismus)
- Cover OD, underneath deviates out, uncover, OD refixates within a second
-
Recovers after blink (intermittent strabismus)
- Cover OD, underneath deviates out, uncover, OD refixates following a blink
-
Delayed recovery after blink (intermittent strabismus)
- Cover OD, underneath deviates out, uncover, OD refixates following several blinks
-
Constant strabismus (when both eyes open, one eye is ALWAYS deviated)
- Stays out indefinitely, only comes in when forced to fixate by covering OS, uncover
OS, instantly goes back out
Describing Strabismus
- Direction
- Laterality
- Frequency Control MAYO Scale
- D vs N
- Magnitude
- Comitancy
- Version/ductions
MAYO Scale – Intermittent Exotropia Control
5 = **constant XT** when observing the patient (without dissociation) 4 = **XT \> 50%** of the time during 30 second observation (without dissociation) 3 = **XT \< 50%** of the time during 30 second observation (without dissociation) 2 = **no XT unless dissociated** (with occlusion); **recovered in \>5 seconds** 1 = **no XT unless dissociated** (with occlusion); r**ecovered in 1-5 seconds** 0 = e**xophoria no XT** unless dissociated (with occlusion); recovers in \<1 second
Strabismus
- Direction
- Laterality
- Frequency
- Dist vs.Near
- Magnitude
- Comitancy
- Version/ductions
Dist vs Near
- Determine treatment options and dist
-
Differential diagnoses:
- ET larger at distance more likely related to pathology (do an MRI 6th nerve palsy
- ET larger at near a more likely related to hyperopia (Acc eso)
Magnitude:
- Treatment = small enough for fusional amplitude to control
- Psycho social factors
-
Large enough to consider strabismus surgery.
- horizontal deviation is ≥ 12 Δ
- Parks 3 Step
- R-L-R / L-R-L pattern with superior oblique palsy (CN4)
- Note: 1mm shift = 22 Δ
- Psycho social factors
- Observe At least14.5Δ ET, at least 8ΔXT (more obvious small deviation)
- Asians, esos more noticeable
- Caucasians exos noticeable
- AfricanAmericans , exos slightly more noticeable
Strabismus
- Direction
- Laterality
- Frequency
- Dist vs.Near
- Magnitude
- Comitancy
- Version/ductions
Comitancy
- < 5 Δ difference in magnitude of strabismus in all positions of gaze at specific testing distance
-
Non-comitant deviations generally of higher risk /Pathalogical Strab
- Paretic
- Restrictive
-
Largest E(T) in right gaze Most symptomatic
- Right 6th nerve palsy (LR)
- Horizontal and vertical strabismus, RH(T) largest in left gaze and right head tilt
- Right SO 4th Nerve
Ductions vs. versions
- Versions = binocular eye movements in the same direction
-
Ductions = monocular eye movements (cover one for EOMs)
- Movement = Tropia / No movement = Palsy
-
Recording: (+) overaction, (-) underaction
- scale of 1 to 4 – can’t cross the midline, it’s a -4
Brown’ssyndrome = SO restriction Both eyes
Psychogenic convergence spasm = eyes want to converge when both eyes are open
- Patient can finally abduct when the target gets so far that the nose blocks it
- Mimics an abducens palsy until you get to the point where it is a monocular duction
- Dysconjugate gaze
beating nystagmus = endpoint nystagmus
Saccades and pursuits
Pursuit testing may be normal despite abnormal saccades. Saccades may be more sensitive in the early detection of motility disturbances
TEST
- 40cm testing distance, 40cm separation
- Evaluate Initiation, velocity, accuracy – 10 cycles Gain calibration
-
Abnormal:
- Slow saccades / lack of coordination / asymmetry between the eyes is abnormal
Note: INO mimics medial rectus impairment. When the eye tries to adduct towards the nose, visible INO, limited to the midline. If one eye hits the target first in a saccade and the other eye slides along, this is a classic INO sign
Eye Movement components
Supranuclear (cortical) pathway
Vestibular pathway (stimulated by ears)
Infranuclear pathway
Infranuclear pathway
- Shared by all pathways
- all 3 are abnormal, problem infranuclear pathway
Tests to see which pathway is damaged:
- Doll’s head: Vestibular pathway
-
EOMs: Supranuclear pathway (VOLUNTARY)
- SN - Brainstem - IN - Eye
-
OKN drum: Supranuclear pathway (INVOLUNTARY)
- Can hold vertically or horizontally
- Optokinetic nystagmus involves both infranuclear and supranuclear pathways
EOMs abnormal / Dolls head normal R/O Vestibular / OKN abnormal Supranuclear problem vs normal malingering
Forced Duction
Test to detect mechanical limitation of motion
An attempt to move the eye forcibly in the direction of gaze limitation while the
patient is attempting to look in that direction (using an anesthetized swab)
Subjective
(+) forced duction = restriction
(-) forced duction = normal, probably paralytic
What determines Type of adaptation
(charactaristics of adaptation)
Suppression major adaptation < 8yo
Important Characteristics of Adaptation
- Age and onset of strabismus
- Duration of strabismus
- Comitancy (History of strabismic surgery, comitancy may change)
-
Type of strabismus
- Infantile ET constant >40-50pd before 4-6mos, surgery consecutive XT ‘current presentation’
As a clinician, you may not be privy to 1 and 2. 3 and 4 may change over time. So, being able to test for the type of adaptation can be a way of gaining insight into all 4 characteristics
Adaptations to Strabismus
Post Critical period
- Close an eye
- Increase fusional amplitudes
- XT, worse on BO ranges (PFV) to control (Not correct), requires more to compensate
- Blind spot syndrome = ET only
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Non-comitancy
- cannot suppress, compensate with head turn/tilt
-
Visual ignoring
- can not suppress, one image not on the fovea, will ignore the ‘blurry’ image, more common with small strabismus or when VA is monocularly reduced
- Difficult if equal VA in both eyes
Strabismus Adaptation
Suppression
ARC
Mono fixation Syndrome
SUPPRESSION
- Cortical phenomenon
- Variable / Active process (recognition of issue, actively signal to resolve the issue with suppression)
-
Respects laterality
- When fixation alternates, suppression shifts to the other eye
-
Respects frequency
- Intermittent strabismic not at risk for amblyopia
-
Depth of suppression – variable
- Suppression develops under natural conditions.
- artificial environment = possible Diplopia
Bagolini density filter bar
Degrades acuity of good eye to force the patient to see double, equalizes the quality of the image on the good eye to see images of the bad ‘how much degradation before the brain will no longer suppress the bad eye?’
Strabismus Adaptation
Suppression
ARC (Binocular adaptation)
Mono fixation Syndrome
Modified Thorington, Maddox Rod, and Worth4Dot are technically considered bi-ocular tests
ANOMALOUS RETINAL CORRESPONDENCE
- BINOCULAR conditions / Cortical phenomenon
- ARC, shift in visual cortex ‘remapping’, gives non-foveal point principal visual direction and motor value of 0
- Requires plasticity of visual system (within critical period)
- pseudofovea“F” Play the role of the fovea, but still not as clear as anatomical fovea (highest density of cones)
- Small active focal suppression of the physiological fovea F also occurs
Binocular conditions, preference – pseudofovea
Monocular conditions, preference – anatomical fovea
- IMPOSSIBLE to have global stereopsis
- will have poor local stereopsis
- Strabismus must be consistent
- 15-18pd deviation, too large, too poor of optical quality
- <6-8yo (plasticity required)
-
Objective angle: Motor movement cover test,
- True objective angle = (“F” - ef) + (ef - F)
- “F” to ef = how much you’ll see on cover test
- Ef to F = measured in Visuoscopy, distance between eccentric fixation point and anatomical fovea
- ET, more commonly constant, (+) due to nasal ef
-
Subjective angle: Magnitude of strabismus that the brain perceives the strabismus to be.
- 10pd constant left ET, the patient reports seeing 4 dots
- Subjective angle = 0 since they’re perceiving 4 dots assumed ARC
Bagolini Striated Glass to assess fusion, suppression, and correspondence
- perceives no dissociation
- Eso = Uncrossed = “V” pattern
- Exo = Crossed = “A” pattern
Strabismus Adaptation
Suppression
ARC (Binocular adaptation)
Mono fixation Syndrome
MONOFIXATION SYNDROME ‘Microtropia’
- Involves small central suppression under binocular viewing conditions
- Clinical profile:
- Reduced monocular acuity (20/25-20/40)
- Normal cover test
- Local stereo is present, but reduced (no global stereo)
- Aniso may or may not be present
- No AMBLYOGENIC refractive error
- The Development of Central Suppression
- Small esotropia(<10pd)
- Closer to fovea than ARC, therefore, better resolution
- Development of eccentric fixation occurs at the pseudofovea “F” = ef
Types of ARC
Harmonious
Unharmonious
Paradoxical
Harmonious ARC (mostcommon)
- Subjective angle = 0
- objective angle = 15pd, subjective angle = 0pd, normal “X” seen on bagolini, NO percieved strabismus
UnharmoniousARC § Rare
- REDUCTION of diplopia
- Subjective angle is smaller than objective angle
- objective angle = 15pd, subjective angle = 5pd
EX. constant left ET, but then with presbyopia it decompensates and gets larger, the ARC has been previously remapped
ParadoxicalARC
- DOES NOT resolve or reduce diplopia
- Subjective angle is larger than objective angle
- objective angle = 15pd, subjective angle = 20pd
• If the patient had strabismus with harmonious ARC and later had surgery, the diplopia becomes much worse
Strabismus Adaptation:
Stereo/Fusion
STEREO & FUSION:
- Provides insight into: Age of onset, frequency, and duration
- Can’t fuse prism = won’t fuse with surgery either
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Testing sensory without motor
- Use prism – move the image to where the eye is to allow for bifoveal fixation
- Exo, neutralize with BI § Eso, neutralize with BO
- Centration point where both lines cross at a random point in space
-
Synoptophores/Major Amblyopscopes
- Equipment to look at the angle of deviation and their binocular potential at a theoretical distance (fixation point)
- Creates simultaneous perception of two images on corresponding points ‘superimposition’
- Can be used to train an amblyopic eye
Strabismus Adaptation:
VA
Refractive Error
Visual Acuity
- Provides insight into: age of onset, laterality, and frequency
- Symmetric good VA binocularly (ie.20/20 intermittent and/or alternating
20/20 with good stereo: Intermittent (Since binocularity required to fuse)
20/20 with poor stereo: Alternating (No fusion since never under binocularity)
- Asymmetric poor VA monocularly
- Difficulty to restore binocularity
- Eye with decreased VA will drift out on its own even after surgery, might need retouch in 10+ years
Refractive Error
- Corrected Refractive error - VA, alignment, and potential to fuse
- Blur, barrier to fusion
- Correction, may improve stereo, but will likely not be perfect o Amblyopia risk factor >2.50D ‘iso’ astigmatism
Always start with correction of refractive error, then follow-up with reassessment of stereo/alignment and VA
