Accommodative and vergence dysfunction

Accommodative and VergenceAccommodative and Vergence
DysfunctionDysfunction
Binocular Vision II
Rabindra Adhikary
ravinems@iom.edu.np

AccommodationAccommodation
Process by which refractive power of
eyes is altered to ensure a clear
retinal image
Association with
– Convergence
– Pupillary Miosis
Near triad

ConvergenceConvergence
 Disjunctive
movement
– Simultaneous,
synchronous,
adduction of both
eyes
 Types
– Symmetric
– Assymetric

Unit of measurement
– Meter angle (MA)
• The amount of convergence required for
each eye to fixate an object located at a
distance from the eyes in the median plane
• Numerically the reciprocal of fixation
distance in meter
– Clinical measurement – Prism Diopter
• 1pd = ? degree

Prism dioptrePrism dioptre
Meter angleMeter angle

 Amount of convergence
– Fixation distance
– IPD
– Formulae
• Tan E = Convergence for a eye
= IPD/Fixation distance (m)
Both eyes = 2 E = IPD (cm) X MA of convergence
Eg: Patient with IPD 6.5 cm fixing at 1/3 m , what is the
amount convergence requirement?

Types
– Voluntary convergence
– Tonic convergence
• Brings eyes from anatomical position of
rest to physiological position of rest
– Accommodative Convergence
– Proximal convergence

Accommodative Convergence &Accommodative Convergence &
AC/A RatioAC/A Ratio
 Convergence elicited by Accomm.
– Amount = AC/A ratio
• The convergence response of an individual to an unit
stimulus of accommodation
• Unit = ∆/D
• Normal range = 4 to 6
– Value above 6 = excessive accommodative convergenc
– Value below 4= Insufficiency
– Calculation
• Heterophoria method
• Gradient Method
• Haploscopic method
• Graphical Method

AC/A ratio calculationAC/A ratio calculation
Heterophoria Method (Calculation)
AC/A = IPD (cm) + ∆n - ∆d
D
Where, ∆n - ∆d= change in deviation from near (33cm) to distance fixation
D = fixation distance in Dioptre
Esodeviation = +ve
Exodeviation = -ve

AC/A ratio calculationAC/A ratio calculation
Gradient method
AC/A = ∆l - ∆o
D
Where, ∆l = deviation with lens
∆o = deviation without lens
D = power of lens
AC/A (Heterophoria > Gradient method)

Classification of AccommodativeClassification of Accommodative
Accommodative Insufficiency
Accommodation fatigue
Accommodative Infacility
Paralysis of Accommodation
Spasm of Accommodation
– Pseudomyopia

Classification of VergenceClassification of Vergence
 Convergence insufficiency
 Divergence Excess
 Basic Exophoria
 Convergence Excess
 Divergence Insufficiency
 Basic Esophoria
 Fusional Vergence Dysfunction
 Vertical Phorias

Accommodative Dysfunctions (AD)Accommodative Dysfunctions (AD)
Accommodation begins at 4 months
of age
Accommodative dysfunction
– response is less than needed for a
given stimulus
Normal accommodative systems is
resistant to fatigue

Signs and Symptoms:Signs and Symptoms:
1.Accommodative insufficiency (AI)1.Accommodative insufficiency (AI)
 Blurred vision, difficulty reading, irritability, poor
concentration
 Asthenopia at end of day
 Excessive convergence might occur in
attempting to accommodate – AC/A relationship
 Amplitude of Accommodation is less than
expected for patient’s age
 Usually fail the flipper test (+/- 2.00D)
 Positive Relative Accommodation (PRA) is less
than –1.50D

2. Accommodation fatigue (AF)2. Accommodation fatigue (AF)
 Blurred vision after prolonged near work
 Accommodative system fails to sustain
accommodation
 S& S ]
– Like Acc. Insufficiency
– except Amp.Acc. is normal
 Amp. Acc. on repeated testing reduces
 Usually fails flipper test (+/- 2.00D)
 Decreased PRA

3. Accommodative Infacility3. Accommodative Infacility
Poor ease in change of
accommodation stimulus
– Pts c/o distance blurring after
prolonged near work and/or
– near blur after prolonged distance work
Fail flipper test (+/- 2.00D)
Might have normal AA
Abnormal Both PRA or NRA

4. Paralysis of accommodation4. Paralysis of accommodation
 Non- presbyopic patient
– loses accommodation monocularly or
binocularly
 Complain : blur
 Paralysis can be caused by many factors:
– Trauma, toxicity, Adie’s Pupil, neuropathy,
drugs (cycloplegic agents)
 Etiology should be known if possible

5. Accommodation spasm5. Accommodation spasm
 Eyes over-accommodates for a stimulus
 Constant parasympathetic innervations of the
near reflex
– Usually not associated with organic disease
 Etiology might be psychogenic
 Distance VA can also be impaired
– Pseudomyopia
Note:
The term accommodative excess can also be used
interchangeably

Etiology: Vergence DysfunctionEtiology: Vergence Dysfunction
1. Convergence insufficiency: Controversial etiology
– Exo deviation at near > distance by 8 Pd
– Low AC/A ratio
– Cause
• Believed to be breakdown of accommodative-convergence
relationship
1. Divergence Excess:
– Exo deviation at distance > near by 8 Pd
– High AC/A ratio
– Innervation etiology
– Condition increases the peripheral field of view
• when patient manifests a strabismus
1. Basic Exophoria
– Equal amount of exo for both distance
– Normal AC/A

Etiology: Vergence DysfunctionsEtiology: Vergence Dysfunctions
4. Convergence excess:
– Eso deviation Near > Distance
– Due to high AC/A ratio
– Increase with age in child
5. Divergence insufficiency
– Eso deviation Distance > near
– Due to high tonic esophoria
– Does not change with time
6. Basic esophoria
– Develops early in life (6-9 months)
– Genetic predisposition
– Normal AC/A

1. Convergence Insufficiency1. Convergence Insufficiency
 Most common symptoms?
 Low Positive Fusional Convergence (10PD
or less)
 79% are exophoric, 18% orthophoric and
3% are esophoric
 Low NPC
 Low AC/A
 Low NRA
– Failure with (+) lenses or the +/- 2.00 flipper
test

2. Divergence Excess2. Divergence Excess
 May be asymptomatic
– Deep suppression
– Anomalous correspondence
 Diplopia and asthenopia
 Distance blur if pt over-accommodates at
distance
 High AC/A ratio
 Normal NPC
 Adequate Positive Fusional Convergence
at near and normal stereopsis at near

3. Basic Exophoria3. Basic Exophoria
Same signs and symptoms as DE
Same angle of deviation at distance
and near
This patient believed to be have
DE , , has acquired CI

4. Convergence Excess4. Convergence Excess
Symptoms of CE?
– Not all have symptoms and asthenopia
Low Fusional divergence amplitudes
at near
Low PRA (less than –1.50 D)
High AC/A ratio

5. Divergence Insufficiency5. Divergence Insufficiency
Low Fusional Divergence Amplitudes
at distance
Low AC/A ratios
Reports diplopia or blur at distance

6. Basic esophoria6. Basic esophoria
At which distance does pt report
symptoms?
Fusional divergence amplitudes not
large enough to compensate
esophoria

Fusional Vergence dysfunctionFusional Vergence dysfunction
 Reduced fusional vergence amplitudes in
divergence and convergence
– Do not have significant Heterophoria
 Most have accommodative problems too
– Fixation Disparity Curve: very narrow with flat
zone indicating poor Vergence adaptation

Treatment Thoughts:Treatment Thoughts:
 Early treatment is important not necessary for
success
– Some can become strabismic especially during
critical period of development
 Not age dependent or restricted
– Motivated 60 year old
– 10 year old
 Does not cause learning disabilities, but…
– Contributes to learning problems
– Vergence anomalies reduce reading scores
– Earlier treatment can help with academic success for
students

Diagnostic procedures:Diagnostic procedures: this is notthis is not
comprehensive (just ones I want to stress to you)comprehensive (just ones I want to stress to you)
Cover Test
– small target to control accommodation
Versions
– Attention to elevation and adduction
– Which muscles most affected?
– Use alternating CT with prism
neutralization in field of question

Diagnostic procedures:Diagnostic procedures:
NPC
– RAF rule
Fusional Vergence Amplitudes (near
and far)
– Measure BI (divergence) first
– Use Accommodative target for near
– Report first blur. Why?

 NRA/PRA
– Measure accommodation with a fixed amount
of convergence
– How does (+) lenses change fusional
vergences?
– How does (-) lenses affect Fusional vergence?
– When a patient reports
• first blur with (+) lenses, First blur with (-) lenses?

Accommodative Amplitude and
Facility
– Monocular
– Push up
– Minus lens method
– +/- flipper

Supplemental Tests:
AC/A ratio: Normal = 4-6:1
– Calculated method
– Gradient method

Supplemental Tests, cont.Supplemental Tests, cont.
Fixation Disparity/Associated Phoria
–Fixation Disparity:
– direct measurement of
misalignment of eyes that occurs
when vision is single and binocular
and clear.
–Associate Phoria:
– amount of prism needed to
neutralize FD

Vergence Facility
– Prism flippers (16 PD BO and 8 PD BI)
– Mean values are 8 cycles/min for
children 5-8 years
– 13 cycles/min for children age 7-14
years

Accommodative Lag
– MEM retinoscopy (objective)
– Nott retinoscopy
– Fused cross-cylinder (subjective)

Treatment OptionsTreatment Options
 Optical correction
– FULL CORRECTION (CYCLOPLEGIC)
 Vision Therapy/Orthoptics
 Medical/pharmaceutical treatment
 Surgery

ReferencesReferences
Binocular Vision & Ocular Motility –
Von Noorden
Orthopitc Management of strabismus
Lab manual for BSV – Bill B. Rainey
WWW.

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