fusional vergence n.
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Fusional vergence. Maddox components of vergence. Tonic Fusional Accommodative Proximal. Maddox’s thoughts. 4 components are independent Additive a given vergence movement can be decomposed into components which are added together to produce the full movement

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maddox components of vergence
Maddox components of vergence
  • Tonic
  • Fusional
  • Accommodative
  • Proximal
maddox s thoughts
Maddox’s thoughts
  • 4 components are
    • independent
    • Additive
      • a given vergence movement can be decomposed into components which are added together to produce the full movement
      • If any one component is insufficient, pts. will have nearpoint complaints
        • asthenopia
specifying the amount of vergence
Specifying the amount of vergence
  • Three basic units of measurement
    • Angular (°)
    • Prism diopters (∆)
    • Meter angles
  • Take distance from target and pd in identical units of measurement
  • Divide pd in half
  • Take inverse tangent of 0.5 pd/distance
  • Double that to get the full angle

d (m)



pd (cm)

prism diopters
Prism diopters
  • most commonly used clinical measure of vergence angle
  • 1∆ (prism diopter) is the tangential deviation of 1 linear centimeter at 1 meter’s distance
    • For ø ≤ 10 deg., tan ø=ø and ∆ = p/d
    • a viewing distance of .4 m( 40 cm) with p = 6 cm (60 mm), the eyes must converge 15∆ (6/.4).
meter angle
Meter angle
  • The meter angle is the amount of vergence required for both eyes to look at an object at 1m distance
  • 1 meter angle = 1/d (in m)
    • 1 meter angle = 1∆/p.d.
proximal vergence
Proximal Vergence
  • Maddox called this component “psychic” vergence
    • the amount of vergence produced by the awareness of a near object
    • In the optometric exam, the phoroptor is a near object that can contribute to a vergence posture.
tonic vergence
Tonic Vergence
  • difference between the anatomical position of rest and the physiological position of rest
  • anatomical position of rest is that which the eyes assume in deep anesthesia, coma, or death
    • divergent
physiological position of rest
Physiological position of rest
  • orientation of the two eyes in the absence of any stimulus to fusion
  • identical to the distance phoria if the eyes are emmetropic or properly refracted
distance phoria
Distance phoria
  • A patient is said to be orthophoric if he/she has no distance phoria.
  • If there is a heterophoria, its direction shows whether tonic vergence is excessive or insufficient
    • If exophoric (eyes divergent), tonic vergence is probably insufficient.
    • If esophoric (eyes convergent), tonic vergence is probably excessive.
distance phoria1
Distance phoria
  • phoria = position of the two eyes is the position of the visual axes relative to one another when all stimuli to binocular fusion have been eliminated.
    • “dissociating” the two eyes
    • assumes that the person is emmetropic or properly corrected
  • If there are visual stimuli for fusion, the position of the eyes will be determined by both fusional vergence and tonic vergence.
  • If the test target is nearer than about 6 m, accommodative vergence will also be present.
dissociating the two eyes
Dissociating the two eyes
  • two ways
    • by covering one eye, as in the cover test
    • by placing a dissociating prism in front of one eye and a measuring prism in front of the other
      • use a value of vertical dissociating prism that is too great to be overcome by fusional vergence in front of one eye (e.g., 7-8∆).




Through dissociating prism

Measuring prism

distance phoria2
Distance phoria
  • If alignment occurs at 0 ∆, the patient is orthophoric.
  • If alignment requires base-in prism, the patient is exophoric.
  • If alignment requires base-out prism, the patient is esophoric.
distance phoria3
Distance phoria
  • Distance phoria measurements assume the target is located at 6 m or greater.
  • Tonic vergence is a significant determiner of the distance phoria.
  • Other factors contributing to distance phorias
    • the position of the eye in the orbit
    • the length of the EOM
    • the positions of the insertions of the EOM.
fusional vergence1
Fusional vergence
  • also known as disparity vergence
    • operates to reduce retinal disparity
  • To see an object singly, the image of the fixated object must falls on corresponding points on the two retinas
corresponding retinal points
Corresponding retinal points
  • Definition: points on the two retinas which, when stimulated, give rise to perception of identical visual direction
  • Fusional vergence movements take place to eliminate noncorresponding retinal stimulation or retinal disparity
    • fusional vergence prevents diplopia
eliciting fusional vergence
Eliciting fusional vergence
  • place a prism in front of one eye
    • The eye will move (fusional vergence movement) to prevent diplopia.
  • uncover a covered eye elicits a fusional vergence movement
    • The eye will move from the phoria position to obtain single binocular vision.
clinical determination of fusional vergence
Clinical determination of fusional vergence
  • Ideally, introduce a small amount of horizontal prism, in equal amounts, before the two eyes
    • Inward movements are positive and outward movements are negative
      • base-out prism induces positive fusional vergence (convergence)
      • base-in prism induces negative fusional vergence (divergence)
clinical tests
Clinical tests
  • at both distance and near (40 cm.)
    • using 20/20 letters as the test target
  • patient is asked to report if the letters blur or become double
  • note prism powers where blur (if it occurs) and where doubling (break) are reported
    • then reduce prism until the target is seen singly (recovery)--and note that value
negative fusional vergence at distance
Negative fusional vergence at distance
  • At optical infinity: base-in prism is added equally before the two eyes as the patient views 20/20 letters
  • What does the blur indicate? Is a blur finding expected in this case? Why or why not?
  • What does the break represent?
  • What does recovery mean?
negative fusional vergence at distance1
Negative fusional vergence at distance
  • Blur indicates the limits of negative fusional vergence
    • now accommodative vergence is called on the supplement fusional vergence
    • in this case, we have to diverge so we would have to relax accommodation
    • Should we be able to relax accommodation at 6 m?
negative fusional vergence at distance2
Negative fusional vergence at distance
  • Break indicates that the total ability of the eyes to diverge to avoid diplopia has been reached.
    • The eyes return to the phoria position at break.
  • Recovery indicates that a negative fusional vergence movement has been made to again obtain single binocular vision.
positive fusional vergence at distance
Positive fusional vergence at distance
  • adds base-out prism equally before the two eyes while the patient focuses on the test target (20/20 letters)
  • patient again reports blur, break and recovery.
  • Should we have a blur finding here?
positive fusional vergence
Positive fusional vergence
  • Blur -- limits of fusional vergence
    • accommodative vergence is being called on to supplement fusional; we should be able to accommodate at distance
  • Break -- limits of accommodative vergence (if there is blur
  • Recovery occurs after the eyes have converged (positive fusional vergence movement).
negative and positive fusional vergence at near
Negative and positive fusional vergence at near
  • same tests but performed at 40 cm
  • expects blur for base-in vergence
    • focusing on a target at 40 cm demands 2.5D of accommodation (D=1/.4m)
    • accommodation is relaxed to supplement negative fusional vergence
expected values for fusional vergence
Expected values for fusional vergence
  • from Morgan (and Bachman)
  • At optical infinity
    • Base-in x/7/4
    • Base-out 9/19/10
  • At 40 cm
    • Base-in 13/21/13
    • Base-out 17/21/11
  • Test base in before base out?
  • Test distance before near?
  • There are aftereffects of prism testing
    • Effects of base in are less than those of base out
    • Effects at distance are less than those at near
    • Start where the aftereffects are least for most accurate determination