4. ConvergenceConvergence
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
6. ConvergenceConvergence
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?
8. 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
9. 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
10. 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)
11. Classification of AccommodativeClassification of Accommodative
DysfunctionDysfunction
Accommodative Insufficiency
Accommodation fatigue
Accommodative Infacility
Paralysis of Accommodation
Spasm of Accommodation
– Pseudomyopia
13. 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
14. 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
15. Signs and Symptoms:Signs and Symptoms:
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
16. Signs and Symptoms:Signs and Symptoms:
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
17. Signs and Symptoms:Signs and Symptoms:
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
18. Signs and Symptoms:Signs and Symptoms:
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
19. 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
20. 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
21. Signs and Symptoms:Signs and Symptoms:
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
22. Signs and Symptoms:Signs and Symptoms:
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
23. Signs and Symptoms:Signs and Symptoms:
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
24. Signs and Symptoms:Signs and Symptoms:
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
25. Signs and Symptoms:Signs and Symptoms:
5. Divergence Insufficiency5. Divergence Insufficiency
Low Fusional Divergence Amplitudes
at distance
Low AC/A ratios
Reports diplopia or blur at distance
26. Signs and Symptoms:Signs and Symptoms:
6. Basic esophoria6. Basic esophoria
At which distance does pt report
symptoms?
Fusional divergence amplitudes not
large enough to compensate
esophoria
27. Signs and Symptoms:Signs and Symptoms:
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
28. 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
29. 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
31. 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)
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?
32. 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)
Accommodative Amplitude and
Facility
– Monocular
– Push up
– Minus lens method
– +/- flipper
33. 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)
Supplemental Tests:
AC/A ratio: Normal = 4-6:1
– Calculated method
– Gradient method
34. 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
35. Supplemental Tests, cont.Supplemental Tests, cont.
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
36. Supplemental Tests, cont.Supplemental Tests, cont.
Accommodative Lag
– MEM retinoscopy (objective)
– Nott retinoscopy
– Fused cross-cylinder (subjective)
37. Treatment OptionsTreatment Options
Optical correction
– FULL CORRECTION (CYCLOPLEGIC)
Vision Therapy/Orthoptics
Medical/pharmaceutical treatment
Surgery