This document discusses different types of vergence eye movements, including fusional vergence and accommodative convergence. It defines fusional vergence as an optomotor reflex that works to maintain eye alignment and retinal image correspondence. Accommodative convergence is described as a reflex linking convergence and accommodation simultaneously during the near response. The ratio between accommodative convergence and accommodation (AC/A ratio) is also discussed, along with examples of normal and abnormal AC/A ratios.

1. Vergences
Tukezban Huseynova, MD
Specialist in Strabismus and Refractive Cornea,
Briz-L Eye Clinic, Baku, Azerbaijan
Tukezban@gmail.com

2. The vergence eye movements are produced
by a group of compound reflexes, only two of
which are identifiable because they are
measurable; these are fusional vergence and
accommodative convergence.

3. The fusional vergences are optomotor reflexes
designed to improve and maintain the alignment
of the eyes so that similar retinal images project
on corresponding retinal areas.

4. ACCOMMODATIVE CONVERGENCE
• Accommodation differs from convergence and miosis in that it
occurs only within the framework of the synkinetic near
reaction.
• The accommodative convergence is a reflex linking
convergence automatically to accommodation and supplying the
most economical innervating method for achieving proper
alignment simultaneously with a change in the dioptric power of
the lens.

5. The following four stimuli produce the
synkinetic near response:
- A blurred retinal image focused posterior to the
plane of the retina.
- Bitemporal disparate retinal images.
- Awareness of near.
- Voluntary convergence.

6. The accommodation and accommodative
convergence activities are in proper relation, the
ratio of accommodative convergence to
accommodation (AC/A) is normal.
An abnormal AC/A is characterized by either a
deficiency or an excess of accommodative
convergence associated with each unit of
accommodation; thus, the resulting abnormal ratio
is either a low AC/A or a high AC/A.

7. NORMAL AC/A
• The normal AC/A in children is pliable, an
attribute that allows adjustments in uncorrected
myopia and exodeviation.

8. ABNORMAL AC/A
- A high AC/A causes more convergence for near
fixation than for distance fixation, with the actual
difference between them being determined by the
severity of the AC/A abnormality, which may vary
from slight to marked.
- A high AC/A may occur in a patient with orthophoric
eyes for distance fixation as well as in the patient with
an esodeviation or an exodeviation.

9. ABNORMAL AC/A
(A) High AC/A ratio, causing near esotropia
despite fully corrective distance hypermetropic
spectacles. (B) Bifocal segment adds compensation
for the high AC/A ratio, permitting straight eyes for
near viewing.

10. - The primarily abnormal high AC/A is unpliable, unlike the
normal AC/A
- The primarily defective high AC/A that causes convergence
excess tends to improve after the patient reaches 8 years of age.
- There is no orthoptic technique that can improve the high
AC/A.
- Surgery on the horizontal rectus muscles may improve the high
AC/A somewhat; the greater the severity of the high AC/A, the
greater is the effect of surgery on the ratio.
ABNORMAL AC/A

11. -A low AC/A causes less convergence for near fixation than
for distance fixation, with the actual difference between
them being determined by the severity of the AC/A
abnormality, which may vary from slight to marked.
-A low AC/A may occur in a patient with orthophoric eyes
for distance fixation as well as in a patient with
esodeviation or exodeviation. The patient with a low AC/A
who is either orthophoric or exodeviated for distance.The
patient with a low AC/A and esodeviation at distance has a
divergence insufficiency.
ABNORMAL AC/A

12. - The low AC/A in convergence insufficiency is a primarily
defective ratio that never improves with age.
- Neither surgery of the horizontal recti nor orthoptics improve
the low AC/A in convergence insufficiency.
ABNORMAL AC/A
- The low AC/A in divergence insufficiency is a relatively
rare clinical entity.

13. At 6 Meters At 0.33 Meter
Normal ratio
Orthophoria Orthophoria
ET = 30 ET = 30
XT = 30 XT = 30
Abnormal ratio
High AC/A
Orthophoria ET = 30
ET = 30 ET = 60
XT = 30 Orthophoria
Low AC/A
Orthophoria XT = 15
ET = 30 ET = 15
XT = 30 XT = 45
AC/A as Determined by Prism and Alternate Cover
Measurements

14. FUSIONAL VERGENCE
• Fusional vergence is an optomotor reflex.
• Fusional vergence is classified according to the plane of eye
movements (i.e., horizontal, vertical, or rotary).
• The maximal amount of eye movement produced by fusional
vergence is referred to as an amplitude. The amplitudes of
horizontal, vertical, and rotary fusional vergence are
measurable; the prism diopter is the unit of measurement
except in incyclovergence and excyclovergence, which are
measured in degrees.

15. HORIZONTAL
Convergence
- Fusional convergence is a reflex that
responds only to the stimulus of
bitemporal disparity of the retinal images.
- The normal fusional convergence
amplitude at 6 meters is 15Δ for fusion
break and 12Δ for fusion restoration.

16. Divergence
- Fusional divergence is a reflex that responds only to the
stimulus of binasal retinal image disparity.
- The normal fusional divergence amplitude at 6 meters is
8Δ for fusion break and 6Δ for fusion restoration.
HORIZONTAL

17. VERTICAL
Positive
- Positive vertical vergence is a simultaneous elevation of the right
eye and depression of the left eye, compensating for a left
hyperdeviation by maintaining a left hyperphoria.
Negative
- Negative vertical vergence is the opposite of positive vertical
vergence, namely, maintaining right hyperphoria by
simultaneous depression of the right eye and elevation of the
left eye.

18. -Incyclovergence is simultaneous incycloduction of each eye to
compensate for excyclodeviation and to maintain
excyclophoria.
- Excyclovergence is simultaneous excycloduction of each eye
to compensate for incyclodeviation and to maintain
incyclophoria.
- The normal patient has an incyclovergence of 6° to 10° and an
excyclovergence of 8° to 12°.
Torsional

19. The innervational factor that produces a vergence
movement that is neither a fusional vergence nor an
accommodative convergence is designated tonic.
Tonic vergences are most commonly referred to as
having a horizontal plane of action and are divided into
tonic convergence and divergence.
TONIC VERGENCES

20. Thank You