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Basic Course Lecture given in Philippine General Hospital, Sentro Oftalmologico Jose Rizal, Lecture modified July 2014
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I. Binocular Vision and Retinal CorrespondenceII. Amblyopia
Alvina Pauline D. Santiago, MDPediatric Ophthalmology & Adult Strabismus
Basic Course Lectures in OphthalmologySentro Oftalmologico Jose RizalPhilippine General Hospital September 2014
Binocular Vision & Retinal Correspondence
Theories of Binocular VisionCorrespondence & disparity
sensory binocular cooperation based on correspondence & disparity
single visual impression, no depth binocular rivalry: diplopia horizontal disparity: depth within Panum’s
fusional space
TermsHoropter
locus of all object pts imaged on corresponding retinal elements at a given fixation distance
Panum’s fusional space or area of SBV region in front of and at the back of the
horopter that still allows SBV allows depth perception
Horopter Elliptical line that
stimulate corresponding points on the retina
Panum’s fusional space Area in front and behind
horopter where objects stimulate non correspondings points and yet are still fusible as one retinal image
Physiologic diplopia
Uncrossed diplopia
Crossed diplopia
Theories of Binocular VisionNeurophysiologic theory
visual stimuli from retina to visual cortex modified and coded
only 25% binocularly driven cells are stimulated equally; 75% graded influence from R & L eye
Macaque monkey: Ar 18; Rhesus: Ar 17-18 Lost binocular neurons do not recover
Binocular Vision Reduced panorama of visionUpright positionFrontal eye positionVisuomotor tasks improvedDepth perceptionOrientation of body to environment
Visual Pathway
Normal Visual Development
Development of Visual Acuity
Macula Development Fine visual
discrimination characteristic of high VA require sharply focused small objects as appropriate stimuli
Amblyoscope or haploscope
Amblyoscope 2 mirrors at elbow
that reflect images from picture slides
arms may be moved to align targets on each fovea
AmblyoscopeSubjective angle
amount in degrees the examiner must move amblyoscope arms for patient to see 2 pictures as superimposed
during binocular viewing conditionsObjective angle
AmblyoscopeSubjective angleObjective angle
deviation measured by alternate prism cover test
during monocular viewing conditions
AmblyoscopeAngle of anomaly
displacement of the true fovea from pseudofovea
zero if NRC; subjective = objective angle (+) if alternate cover test (objective angle)
is not equal to subjective angle
Worth’s level of fusionFirst degree (simultaneous perception)
Dissimilar targets presented Perceived at the same time in the same
visual directionSecond degreeThird degree
Worth’s level of fusionFirst degree (simultaneous perception)Second degree (flat fusion)
similar targets with dissimilar components (monocular suppression checks)
Third degree
Worth’s level of fusionFirst degree (simultaneous perception)Second degree (flat fusion)Third degree (stereopsis)
Same targets as 2nd degree + disparity
First degree simultaneous
perception
2nd degree flat fusion
3rd degree Stereopsis
Normal retinal correspondence RE: circle LE: black dot
Orthotropic Black dot in circle
Normal retinal correspondenceOrganization of visual space is such
that the visual direction of each fovea is the same
Angle of anomaly = 0Patients with NRC always use fovea as
center of reference
NRC, with strabismus
To see black dot in circle, need to move arms of amblyoscope total of 40 PD
Difficulties in TestingNRC and strabismus
If with dense large regional suppression, no subjective angle, difficult to superimpose images
If monofixator, use targets for peripheral retina
Harmonious ARC subjective angle = 0
measured under binocular conditions
Pseudofovea compensates for angle of deviation
No subjective misalignment
Unharmonious ARC
pseudofovea does not compensate fully for angle of deviation
Angle of anomaly = objective angle - subjective angle
AmblyoscopeMeasures fusional vergenge amplitudesAngle of deviationArea of suppressionRetinal correspondenceTorsion Instrument convergence
Terms
Retinal correspondence single vision: hallmark
ARC vs NRCRetinal disparity & rivalry:
diplopia and visual confusion
Abnormalities of binocular visionDiplopiaVisual confusionSuppressionHorror fusionisAnomalous retinal correspondence
Diplopia vs Visual ConfusionDiplopia
Object of interest seen by fovea of one eye and peripheral retina of the other eye
Visual confusion Fovea of both eyes (or corresponding
retinal points) sees 2 objects of interest interpreted as coming from the same point in space
Diplopia vs Visual Confusion
SuppressionSuppression: alteration of visual
sensation that results in inhibition or prevention of one eye’s image from reaching consciousness
Physiologic suppression prevents physiologic diplopia from reaching consciousness
Central vs peripheral suppressionCentral:
pathologic extension of retinal rivalry prevents foveal image of deviating eye
from being perceived
Peripheral: Prevents awareness of the image on
peripheral retina (2nd image)
Suppression ScotomaEsotropia Exotropia
Monocular vs Alternating suppressionMonocular: unidirectional
Dominant eye always predominate over image from deviating eye
Alternating: bidirectional Suppression switches between the two
eyes
Facultative vs Obligatory SuppressionFacultative
Present only when eyes are deviated
Obligatory Present at all times, whether eyes are
deviated or aligned
Amblyopia
Definition: Amblyopia
Etymology: dullness of vision Greek:
amblyos = dull Stem: ops = vision
Observer (MD) sees nothing, and the patient sees very little
von Graefe
DefinitionUnilateral or bilateral decrease in VA
caused by pattern vision deprivation or abnormal binocular interaction for which no cause can be detected by physical examination, and which in appropriate cases, reversible by therapeutic measures
von Noorden
PrevalenceApproximately 2-2.5% of general
population has amblyopia
Military Recruits 1-3.2% Preschool children 0.5-3.5% Ophthalmic patients 4-5.3%
Normal Visual Development
Basic Mechanisms Abnormal binocular interactionFoveal pattern vision deprivationCombination of both
Susceptible Period Most sensitive first 2-3
years Decreases until age 6-
7 years complete visual
maturation retinocortical pathways
and visual centers resistant to abnormal visual input
Classification Reversible (functional)
Strabismic amblyopia Anisometropic / ametropic amblyopia Visual deprivation amblyopia Idiopathic amblyopia Toxic / Nutritional amblyopia
Irreversible (organic) Amblyopia in nystagmus Other ocular pathologies
Strabismic Amblyopia Higher prevalence in ET than XT because of
nasotemporal asymmetry of retinocortical projections
ET: fovea of deviating eye competes with strong temporal field
XT: fovea competes with weaker nasal field
Strabismic Amblyopia
always unilateral, caused by active inhibition of retinocortical
pathway originating from fovea of deviating eye due to visual confusion
lack of adequate stimulation of the foveaDuration of strabismus rather than age
at time strabismus develops correlates more closely with amblyopia
Sensory AdaptationsDouble vision: diplopia
obj of interest seen by fovea of one eye and peripheral retina of other eye
Visual confusion fovea of each eye sees 2 different obj
interpreted by brain to be in the same visual direction
Diplopia vs Visual Confusion
Suppression ScotomaEsotropia Exotropia
Lateral Geniculate Nucleus in Strabismic Amblyopia
NORMAL
Normal PET Scan
Relative cerebral glucose metabolism most active in tip of visual cortex
equal activity with monocular viewing of either eye
Right eye viewing
Left eye viewing
Strabismic Amblyopia Normal right eye
active glucose metabolism in tip of visual occipital cortex extending to Area 19 and 7
Amblyopic left eye decreased glucose
metabolism at tip activation of Areas 19
and 7
Right eye viewing
Left eye viewing
Strabismic Amblyopia Amblyopic left eye
minimal glucose metabolism in visual cortex
Normal right eye active glucose
metabolism left temporal lobe
more active than right
Left eye viewing
Right eye viewing
Other AssociationsEccentric FixationAnomalous CorrespondenceLoss of fusionRetinal disparity and rivalryCrowding phenomenonSmooth pursuit asymmetry
Visual Acuity Prediction
Amblyopia vs SuppressionBoth occur to eliminate visual confusion
from dissimilar retinal imagesSuppression occurs only under
binocular conditionsAmblyopia persists after closure of
fixating eye
Anisometropic AmblyopiaActive inhibition of fovea Eliminate sensory interference caused
by superimposition of a focused and defocused image (abnormal binocular interaction)
Aniseikonia may be a factorFoveal pattern vision deprivation
Normal PET Scan
Relative cerebral glucose metabolism most active in tip of visual cortex
equal activity with monocular viewing of either eye
Right eye viewing
Left eye viewing
Anisometropic Amblyopia Greater glucose
metabolism when sound eye (left) is viewing
Note contralateral hemisphere activation with either eye viewing
Left eye viewing
Right eye viewing
Visual Deprivation Amblyopia
Disuse or understimulation of retinaUnilateral more severe than bilateralBoth pattern vision deprivation and
abnormal binocular interaction are factors in monocular
Only pattern vision deprivation in binocular
Mechanism of Ambyopia
Causes AbN binoc Forminteraction Deprivation
Strabismus + -Anisometropia + +Visual Deprivation
Unilateral + +Bilateral - +
Organic AmblyopiaSuperimposed functional component
can be improved with amblyopia therapy
Wrong orientation of retinal receptors?Changes in lateral geniculate nucleus
and striate cortex
DiagnosisFixation preference
but many normal patients have fixation preference
Crossed fixation does not always imply absence of
amblyopia
10 PD Base Up Test
DiagnosisVisual acuity
difference in acuity in 2 eyes but certain small difference exist in normal
population difference of 2 lines for most clinical
purposes
Amblyopia TherapyOcclusion or patching even in
nystagmus1 week per year of life then reevaluate
does not signify end of therapy evaluate occlusion amblyopia
Full time vs part timeRole of tapering
Amblyopia Therapy3-6 weeks in older child because of
schoolRationale:
force to use the bad eye allows neural circuitry to be reestablished
Occlusive Patch under Eyeglasses
Alternative to PatchingPenalization
Atropine (Hunter, Johns Hopkins protocol) Optical penalization (over plus: fogging) Neutral density filters Blurring better eye by any means
Factors Affecting RecoveryStage of maturity of visual connections
at which abnormal visual experience began
Type of abnormal visual experience amblyopia more common in ET than XT may be related to nasotemporal
asymmetry (stronger temporal hemifield)
Factors Affecting RecoveryDuration of deprivationAge at which treatment was startedComplianceNeurologic statusPsychological and psychosocial
considerations
Problems with Amblyopia TherapyPatient compliance & acceptanceParental understanding of rationaleParent-child dynamicsPoor follow-upSmart children memorize charts!Differing methods of assessmentWhen to stop patching?
Results of Treatment
Single optotype improves more rapidly than line acuity
Crowding has prognostic valueSingle E acuity represents true
potentialDifferent charts, different results
Normalization of fixation
Timing of Surgery In general, maximize amblyopia
treatment prior to straightening eyes Enhances fusion-lockMost of the time, more practical to start
patching, continue even after surgery
References
Rosenbaum & Santiago: Clinical Strabismus Management
Von Noorden: Binocular Vision and Ocular Motility
Wright: Pediatric Ophthalmology and Strabismus Taylor:Pediatric Ophthalmology Nelson:Pediatric Ophthalmology Moses & Hart:Adler’s Physiology of the Eye PEDIG Amblyopia Studies
Thank you