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29 Cards in this Set
- Front
- Back
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Dissociated Heterophoria
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(measures vergence posture)
*aiming TENDENCY of vergence system *only occurs when sensory fusion is disrupted by dissociaton, which is usually doen by occluding one eye (alternate cover test) TYPES OF PHORIA: 1) orthophoria: both eyes tend to aim directly at target, both horizontally and vertically 2) esophoria (E): both eyes tend to aim closer than target (pt sees "against movement") 3) exophoria (X): both eyes tend to aim farther than target (pt sees "with movement") 4) hyper (H) or hypophoria (Ho): vertical phorias in which one eye tends to aim above (hyper) or below (hypo) target (perception is opposite deviation) |
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Base In/Base Out Prism Flippers
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*alternate 8 BI/BO, flipping when pt sees clear and singly
*record number of flips in 30 second intervals for 2 minutes EXPECTED RESULTS: *pt should not slow much in teh 2 minutes *results vary greatly with age, testing method, etc *expect about 15 cpm for 16+yo; 7 cpm for 8 yo |
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Relative Vergence Range
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(more thorough assessment of vergence amplitude)
*measures fusional vergence ranges by inserting progressively stronger prism until end point (first blur and diplopia) and then reduce prisim power until recover (resume single vision) *inspects accommodative freedom from convergence/divergence *normal sensory fusion must be present to be valid PRC (positive relative convergence): used base-out to stimulate convergence NRC (negative relative convergence): base-in for divergence **if pt doesn't report diplopia or notice target is moving sideways, sensory suppression is occurring and test is invalid** |
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Measuring Vergence
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AMPLITUDE: maximum ability to converge/diverge
FACILITY: speed of change of vergence (can't be measure independent of accommodation) POSTURE/ACCURACY: the aiming tendencies of the two eyes relative to one another and the target; refers to any habitual tendency to over/under converge |
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Near Point of Convergence (NPC)
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(measures vergence amplitude)
*performed by moving small target gradually closer to eyes until convergence ability is exceeded -objective endpoint: dr notices failure to converge -subjective endpoint: pt observes diplopia CLINICAL IMPORTANCE: *minimum "strength" requirement for nearpoint tasks *greatly influenced by accommodation EXPECTED RESULTS: *break: 6.4 +- 1.8 cm *recovery: 10.2 +- 4.3 cm |
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Traditional Classifications of Vergence by E. E. Maddox
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TONIC VERGENCE: underlying level of vergence activity in the absence of a target
FUSIONAL VERGENCE: vergence due to binocular target disparity ACCOMMODATIVE VERGENCE: vergence due to change in accommodation PROXIMAL VERGENCE: vergence due to a mental or psychological awareness of a target nearness |
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Sensory Aspects of Vergence Function
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*normal vergence function requires good visual sensitivity in both eyes and normal sensory fusion
-amblyopia: common condition that interferes with normal vergence function because retinal disparity -normal vergence function is not possible when deep sensory suppression is present (suppression=temporary turn off of eye) *sensory fusion can only maximally develop when motor responses are predictable, steady, and consistently accurate *motor fusion can only be maximally predictable, steady, and consistent when there is normal sensory fusion support |
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Bare Essentials of Vergence Anatomy and Neuroanatomy
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*EOM are skeletal (striated) muscles innervated by the somatic nervous system
-lateral rectus: CN VI (abducens) -superior oblique: CN IV (trochlear) -all rest: CN III (oculomotor) *innervation to vergence is neurologically linked to accommodation via near triad *increase in accommodation = increase in vergence activity -AC/A ratio: accommodative convergence due to accommodation |
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Primary Stimulus for Vergence Adjustments
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***BINOCULAR RETINAL IMAGE DISPARITY***
CROSSED DISPARITY: converge beyond target; image seen by RE is left of image seen by LE; temporal disparity; cross physiological diplopia or heteronymous diplopia UNCROSSED DISPARITY: converge nearer than target; image seen by RE is right of image seen by LE; nasal disparity; uncrossed physiological diplopia or homonymous diplopia |
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Components of Vergence
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1) MOTOR (muscular): neuromuscular process required to adjust the aim of both eyes to bifixate on target
2) SENSORY (neural): "sensory fusion" involves the neural processes of binocular vision that enables the brain to merge the two monocular images into a unified single binocular image |
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Calculate Vergence Demands:
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V(prism diopters) = pd(cm)/target distance(m)
NOTE: prisms are usually only used in dysfunction of the vergence process because it bends incoming light |
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Possible Symptoms of Vergence Dysfunction
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*diplopia (especially with new condition)
*headache in temporal and frontal regions *loss of comprehension with reading *avoidance of certain near-point activities *reduced facility *loss of place when reading *fatigue when reading *general asthenopia |
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Heterotropia (tropia; strabismus)
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*an abnormal condition of vergence posture in which binocular vision is absent or abnormal and only one eye is aimed directly at the target or regard
ESOTROPIA (ET): other eye aimed closer than target (crossed eyes) EXOTROPIA (XT): other eye aimed farther than target HYPERTROPIA (HT): eye aimed above target HYPOTROPIA (HoT): eye aimed below target (pt may experience diplopia when strabismic, or may suppress the central vision of the deviating eye) DIAGNOSE: use unilateral cover test to see strabismus; eye will remain displaced after removal of occlusion |
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Differential Diagnosis: Phoria vs. Tropia
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*unilateral cover test used to diagnose condition of tropia
-if eye doe snot return to a position of bifixation when occluder is removed, tropia has been demonstrated |
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Possible Social/Mental Health Implications of Strabismus
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*retrospective study found that children with exotropia had three times greater risk than controls to develop mental health conditions (no difference with esotropia)
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Measuring Vergence Posture: Heterophoria
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1) Cover/uncover test (aka alternate cover test) with prism neutralization
-esodeviation: use base-out -exodeviation: use base-in --> moves light to where eye IS so they don't need to diverge/converge eyes to see 2) Von Graefe phorias in phoroptor 3) Maddox rod: -> hold rod in certain position = vertical red line -> turn rod 90 degrees = horizontal red line -> forces dissociation |
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Vergence posture in non-primary gaze positions:
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1) primary gaze position refers to the straight-ahead position of the eyes
2) non-primary gaze positions usually induce an increased (eso-ward) vergence posture change |
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Binocular Vision: corresponding retinal points
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LEFT Visual Field:
-RE: temporal retina -LE: nasal retina RIGHT Visual Field: -RE: temporal retina -LE: nasal retina UPWARD Visual Field: -R and L: inferior retina DOWNWARD Visual Field: -R and L: superior retina **the retinal points in the right and left eyes that receive the image of the target are said to be corresponding** |
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Binocular Vision, Vergence Posture, and Perception of Spatial Location
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*all light entering the eyeball must pass through the nodal point at the exact geometric center of the eye
*we LEARN through developmental experiences the relationship between where objects are in real space and where the image of those objects fall on the retina *after learned, relationship becomes FIXED and REFLEXIVE (when R temporal retina is stimulated, we move L to fixate target) *because spatial perception becomes "hardwired", it can lead to perceptual illusions when normal binocular vision is disrupted (ie. dissociating to measure phoria) *Phi Phenomenon: perceived movement in the absence of true target movement by illusion |
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Important Points to Understand Abnormal Diagnostic Test Results:
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1) patients who are diagnosed with these conditions have ABNORMAL vergence postures end do not necessarily follow the rules for normals
2) Patients who have abnormal vergence posture will often regulate accommodation in such a way as to MINIMIZE the effects of abnormal vergence 3) patients with abnormal vergence posture resist tests that require them to make a vergence change in the direction opposite to their normal vergence posture |
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Classic Duane-White Diagnostic Categories:
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*basic esophoria
*basic exophoria *convergence insufficiency (CI) *convergence excess (CE) *divergence insufficiency (DI) *divergence excess (DE) |
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Basic Esophoria
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*eso at 6m and 40 cm
*reduced divergence ranges *reduced PRA *possible excessive binocular lag of accommodation *reduced accommodative and vergence facility (especially minus and base-in) |
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Basic Exophoria
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*exo at 6m and 40cm
*reduced convergence ranges *reduced NRA *reduced binocular lag of accommodation *reduced accommodative and vergence facility (especially plus and base-out) |
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Convergence Insufficiency (CI)
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*high exo at 40cm
*normal phoria at 6m *reduced binocular lag of accommodation *reduced PRC *reduced NRA *reduced accommodative and vergence facility (especially plus and base-out) *possible intermittent 6m blur after near work |
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Convergence Excess (CE)
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*high eso at 40cm
*normal phoria at 6m *possible increased binocular lag of accommodation *reduced NRC *reduced PRA *reduced accommodative and vergence facility (especially minus and base-in) |
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Divergence Insufficiency (DI)
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*high eso at 6m
*normal phoria at 40cm *reduced 6m divergence ability |
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Divergence Excess (DE)
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*high exo at 6m
*normal phoria at 40cm *reduced 6m convergence ability *often intermittent strabismus *often photophobia |
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Binocular Dysfunction of Vision
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*generally decreased range and facility of accommodation and vergence
*phoria may be eso or exo *usually reduced stereopsis |
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Accommodative Insufficiency
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*reduced accommodative ability not associated with normal aging
*low NPA *excessive lag of accommodation *reduced PRA *reduced monocular minus lens to blur *reduced accommodative facility (especially minus) |
