2 Maddox components of vergence TonicFusionalAccommodativeProximal
3 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 movementIf any one component is insufficient, pts. will have nearpoint complaintsasthenopia
4 Specifying the amount of vergence Three basic units of measurementAngular (°)Prism diopters (∆)Meter angles
5 AngularTake distance from target and pd in identical units of measurementDivide pd in halfTake inverse tangent of 0.5 pd/distanceDouble that to get the full angled (m)RR’pd (cm)
6 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 distanceFor ø ≤ 10 deg., tan ø=ø and ∆ = p/da viewing distance of .4 m( 40 cm) with p = 6 cm (60 mm), the eyes must converge 15∆ (6/.4).
7 Meter angleThe meter angle is the amount of vergence required for both eyes to look at an object at 1m distance1 meter angle = 1/d (in m)1 meter angle = 1∆/p.d.
8 Proximal Vergence Maddox called this component “psychic” vergence the amount of vergence produced by the awareness of a near objectIn the optometric exam, the phoroptor is a near object that can contribute to a vergence posture.
9 Tonic Vergencedifference between the anatomical position of rest and the physiological position of restanatomical position of rest is that which the eyes assume in deep anesthesia, coma, or deathdivergent
10 Physiological position of rest orientation of the two eyes in the absence of any stimulus to fusionidentical to the distance phoria if the eyes are emmetropic or properly refracted
11 Distance phoriaA 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 insufficientIf exophoric (eyes divergent), tonic vergence is probably insufficient.If esophoric (eyes convergent), tonic vergence is probably excessive.
12 Distance phoriaphoria = 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 eyesassumes that the person is emmetropic or properly corrected
13 QualifersIf 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.
14 Dissociating the two eyes two waysby covering one eye, as in the cover testby placing a dissociating prism in front of one eye and a measuring prism in front of the otheruse 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∆).
16 Distance phoriaIf 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.
17 Distance phoriaDistance 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 phoriasthe position of the eye in the orbitthe length of the EOMthe positions of the insertions of the EOM.
18 Fusional vergence also known as disparity vergence operates to reduce retinal disparityTo see an object singly, the image of the fixated object must falls on corresponding points on the two retinas
19 Corresponding retinal points Definition: points on the two retinas which, when stimulated, give rise to perception of identical visual directionFusional vergence movements take place to eliminate noncorresponding retinal stimulation or retinal disparityfusional vergence prevents diplopia
20 Eliciting fusional vergence place a prism in front of one eyeThe eye will move (fusional vergence movement) to prevent diplopia.uncover a covered eye elicits a fusional vergence movementThe eye will move from the phoria position to obtain single binocular vision.
21 Clinical determination of fusional vergence Ideally, introduce a small amount of horizontal prism, in equal amounts, before the two eyesInward movements are positive and outward movements are negativebase-out prism induces positive fusional vergence (convergence)base-in prism induces negative fusional vergence (divergence)
22 Clinical tests at both distance and near (40 cm.) using 20/20 letters as the test targetpatient is asked to report if the letters blur or become doublenote prism powers where blur (if it occurs) and where doubling (break) are reportedthen reduce prism until the target is seen singly (recovery)--and note that value
23 Negative fusional vergence at distance At optical infinity: base-in prism is added equally before the two eyes as the patient views 20/20 lettersWhat 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?
24 Negative fusional vergence at distance Blur indicates the limits of negative fusional vergencenow accommodative vergence is called on the supplement fusional vergencein this case, we have to diverge so we would have to relax accommodationShould we be able to relax accommodation at 6 m?
25 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.
26 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?
27 Positive fusional vergence Blur -- limits of fusional vergenceaccommodative vergence is being called on to supplement fusional; we should be able to accommodate at distanceBreak -- limits of accommodative vergence (if there is blurRecovery occurs after the eyes have converged (positive fusional vergence movement).
28 Negative and positive fusional vergence at near same tests but performed at 40 cmexpects blur for base-in vergencefocusing on a target at 40 cm demands 2.5D of accommodation (D=1/.4m)accommodation is relaxed to supplement negative fusional vergence
29 Expected values for fusional vergence from Morgan (and Bachman)At optical infinityBase-in x/7/4Base-out 9/19/10At 40 cmBase-in 13/21/13Base-out 17/21/11
30 Why? Test base in before base out? Test distance before near? There are aftereffects of prism testingEffects of base in are less than those of base outEffects at distance are less than those at nearStart where the aftereffects are least for most accurate determination