Griffin; pp 385-395; 416-427

Richman pp. 15-22, Activity D-17, 18 and D 24: (Bernell Guide) E-1, E-2: E-7 to E-12; E-15 to E-18

Press Chapter 17

I. Introduction: Vergence therapy is necessary for many patients to achieve clear, single and comfortable binocular vision. Although this laboratory is designed to augment the lecture material on convergence dysfunction, it is important to remember that many patients with vergence dysfunction require accommodative therapy as well. The artificial separation of non-strabismic binocular dysfunction into neat and separate categories is a necessity when learning, but is not the case in real patient encounters (...the crowd falls into a hush as Dr. A.F. steps off his little soapbox...).

A. There are several general classifications of vergence dysfunction

1. Convergence insufficiency

2. Convergence excess

3. Inefficient binocular vision (general skills)

4. Divergence excess and insufficiency usually result in an intermittent or constant strabismus. They will be treated in a later lab.

B. Types of vergence: We learned in pre-clinic of the four components of vergence according to Maddox. They were proximal, tonic, accommodative and fusional vergences.

1. It has been shown that vergence therapy has positive long term benefits to fusional vergence.

2. Traditional thought had it that AC/A ratios did not change appreciably after vision therapy. This historical icon is hard to move, but recent clinical research establishes that an AC/A ratio is, in fact, quite adaptable. It is also true that much of therapy is designed to converge beyond and diverge behind the plane of accommodation.

3. The effects of vision training on proximal vergence are under study. The importance of proximal cues to our vergence response have (hopefully) been communucated to you in the past year!.

4. The effects of vision therapy on tonic vergence control remain to be elucidated.

C. Vergence skills (Von Graefe) have been traditionally described as a single range in three steps: blur, break and recovery. Griffin describes TEN criteria for normal vergence function. Most of these were elaborations of phoroptor testing done in a PC exam. I will allow you to read this in all it's gory detail, and offer a brief synopsis here.

1. Vergence fusional ranges should be sufficient for flat fusion targets (like the acuity chart) with the absence of suppression.

2. Vergence ranges should be sufficient without blur or break of fusion.

3. Recoveries to clear and single flat fusion targets should be sufficient.

4. Vergence ranges should be sufficient (blur or break) without a loss of stereopsis

5. Vergence ranges should be sufficient without discomfort.

6. Vergence ranges should be sufficient with proper facility and sustaining skills.

D. Once a diagnosis of a vergence dysfunction is made, the next task is to plan a vision therapy program around the individual needs of a particular patient. As a general rule, it is very important to start a patient with tasks he/she can complete without excessive strain or difficulty. It is very important for a doctor to find the skill level of the patient in each of the four binocular modalities.

E. The goals of vergence therapy are to achieve sufficient ranges to flat fusion or stereoscopic targets with the various devices presented today. Achieving or exceeding Morgan's expecteds is certainly a goal of therapy (see Tab. 1-2 in Scheiman).

F. Vergence facilities (BI/BO flippers) should be developed to a point where the 20/20 vergence rock rule is met. This is also in Griffin. Your assignment (if you choose to accept it) is to look it up. The importance of vergence facility cannot be underestimated; it tests jump vergence ability while forcing the accommodative system to remain at a steady state.

- The 20/20 rule is noble, but most practitioners settle for 8BI/BO facility @15 cycles/min.

II. Now that you are familiar with the four binocular vision skill levels, the next question on your lips is, .."wow, that's neat, but how do I know when my patient is ready to go from one skill level to the next?" Thankfully, Richman and Cron (Bernell Guide, pg. 8) describe this progression quite nicely. (see Bernell guide, pg. 15 for more details).

A. O.K. guys, the stages here are quite similar to those for accommodative dysfunction. In fact, only a few words have to be changed to modify the diatribe on accommodation to a diatribe on vergence skills....In fact, it would seem that Richman has done exactly that !!

B. Awareness of error is the first step. In this case, the change is from brief physiological diplopia to clear single vision WITHOUT SUPPRESSION. This is the control level.

C. Vergence ranges, facilities and efficiency should be increased in the control level. Distractive stimuli should be introduced as skills improve (ie cognitive demands)

D. After these skills are internalized, the patient has reached the automatic level.

E. This should be accomplished with flat fusion and stereoscopic targets.

F. DON'T FORGET ABOUT PLUS LENSES (if accepted).

**H. PLEASE DON'T FORGET TO WORK ON BOTH BO AND BI RANGES WHEN DOING VERGENCE THERAPY...NO MATTER WHAT DYSFUNCTION OF VERGENCE THE PATIENT MAY HAVE!

**General techniques to increase vergence skills fall into two broad categories: instrument vergence techniques and "free space" techniques. Only free space techniques will be covered in this lab.

III. At the Transitional Level: Vergence therapy in free space may begin with awareness of flat fusion and anti-suppression work.

A. Pt. should practice "walk away" or "walk towards" regimens to maintain fusion and no suppressions at different vergence demands. This sort of gradual change in vergence demand is known as smooth vergence. This is an excellent way to begin increasing vergence ranges. The techniques to be reviewed in the Bernell guide for this section are:

1. Box X-O (D-24, home VT section)

2. Pola-Mirror (see below)

3. Pencil push-up (E-1, E-2)

B. The pt should, shortly after initiating therapy, start work on the techniques listed in this section. These techniques are more dynamic and versatile than the previous tests, as they more accurately measure suppression and alignment of the eyes. The techniques to be reviewed in the Bernell guide for this section are:

1. Physiological diplopia (Brock) string (D-17, Home VT section)

2. Barrel cards (Home VT section)

Because of it's length and adjustable balls, the Brock string is the most used of this group.

a. first, it is necessary to begin with the three balls in a sort of standard alignment. Place the first ball at 12 ", and each subsequent ball 12" separated.

b. smooth vergence skills are improved as the pt slowly converges or diverges to a slowly moving bead. Any of the three beads can be used to train smooth vergence skills.

- to learn this, it may be useful for the doctor (you) or the pt. point to the fixation bead as it moves toward or away from the patient; these kinestetic cues help the pt. learn smooth vergence

- demand is increased as a closer (for convergence enhancement) or more distant (for divergence enhancement) target is fixated or the target is moved (Brock string)

- a more challenging way to work smooth vergence is to have the pt slowly change fixation from one target to another as if an insect was crawling on the string from one bead to another.

c. jump vergences may be taught by "jumping" from one target to another either closer to the pt. (for convergence enhancement) or farther away (for divergence enhancement).

IV. At the Binocular Level: we enhance vergence skills and introduce stereopsis into therapy

A. It is important to remember that these artificially designated levels of binocular skills ARE CONTINUOUS WITH EACH OTHER! Therefore, many techniques discussed as transitional level tasks may be modified to fit into the binocular level. It is important to use some of the "early" binocular level techniques to gradually move a patient forward to the next binocular skills level.

1. Box X-O or pencil push-ups may be completed with the addition of a jump prismatic demand (loose prisms or prism flippers)

2. Brock string activites are brought into the binocular level of therapy by introducing additional jump prismatic demand (loose prism or prism flippers).

3. In both cases, fusional vergence demand is increased, while accommodation must remain at a relatively steady state.

B. Pt. should then work with loose prisms (BI and BO) in a "loose prism vergence rock". The rapid change in vergence demand is known as jump vergence. This is an excellent , but more difficult way to continue increasing vergence ranges as well as efficiency and facility. An additional advantage is that may also be used alone, with ordinary (ie real) targets. It is still a good idea to have suppression checks, although an observant doctor (you) will be able to detect suppression by the patients vergence eye movements (or lack thereof). This procedure can also be done effectively for distance targets. The techniques to be reviewed in the Bernell guide for this section are: Loose prism rock (E -16, E-17)

C. Vectographs and tranaglyphs have already been seen in lab. They present a different perspective of an object to each eye (ie binocular disparity). This is accomplished with cross polarization (Polaroid glasses) or color cancellation (red/green glasses). They either have a fixed disparity (fixed vecto. or anag.) or a variable disparity ("sliding" vectograph or tranaglyph. The fixed vectograph (tranaglyph) is on one sheet, and the amount of fusional demand is pre-set. In a "sliding"vectograph" (tranaglyph), the images presented to each eye are on separate slides (2) which allows for variability in the amount of vergence demand presented. In any case, suppression checks are included (one eye sees an object that the other does not). The techniques to be reviewed in the Bernell guide for this section are:

i. Vectographs (E-15)

ii. Tranaglyphs (E-15)

1. The fixed types usually are the ones to begin therapy with.

a. smooth and jump vergences should be worked

b. the entire procedure can be repeated with loose BO and BI prism, for added excitement

2. The variable type are a bit more versatile and advanced.

a. smooth and jump vergences should be worked

b. the entire procedure can be repeated with loose BO and BI prism, for added excitement

3. Because of the disparity created between the images seen by each eye, these targets will be seen stereoscopically. There are several ways then to monitor suppression. If there is suppression , two changes will be noted.

a. suppression checks will detect it

b. loss of stereopsis or float will detect it

4. In addition, any abnormalities in spatial awareness may be unmasked with this technique. The ability to perceive depth (float) is only part of spatial perception. Localization, the ability to "place " the target in space compared to another target in the vectrogram or the pt's. own finger, is also important. SILO is another perceptual outcome of the vectogram. It is based on size constancy (remember your "Monsense" class. In general, as BO demand is increased, the target will appear closer (in) and smaller. This is the "SI" part. As BI vergence is increased, the target(s) will appear to move away (out) and get larger. This is the "LO" part.

D. Eccentric circles (both fixed and variable) can be used as a very advanced binocular level technique to internalize vergence skills. It requires fusion of separate targets ("circles") in a crossed (chiascopic) or uncrossed (orthopic) way. In general chiascopic fusion will develop convergence skills in this procedure. Chiascopic fusion is considered easier to grasp than orthopic fusion. In this procedure , orthopic fusion will develop divergence skills. A third target in depth will be perceived as fusion is achieved. This is a very valuable tool, because it forces the pt to fuse separate targets by converging or diverging outside the plane of accommodation. The techniques to be reviewed in the Bernell guide for this section are: Lifesaver Card (E-18)

*You may wish to perform chiascopic and orthopic fusion now,...before lab. To reward your dedication to learning, I offer "chiascopic thumbs"

1. Separate your thumbs by 2" and hold them at 40 cm. in front of your nose.

2. Slowly follow an imaginary bug from your thumbs towards your nose.

3. As you converge, try to pay attention to the thumbs and keep them clear.

4. As you converge, each thumb will become diplopic....you’re getting there!

5. Eventually, you will reach a point where a third, clear thumb will appear in front of the other two (real ) thumbs. Your real thumbs will be blurry and the third thumb should be clear.

6. You have just chiascopically fused...congratulations!

7. To orthopically fuse, you must attempt to follow that imaginary bug away from your nose! This is usually considered a more difficult task.

V. At the Integrated Level: At this level extreme vergence demand is joined by additional demands on the accommodative and oculomotor systems.

A. It is important to remember that these artificially designated levels of binocular skills ARE CONTINUOUS WITH EACH OTHER! Therefore, many techniques discussed as binocular level tasks may be modified to fit into the integrated level. It is important to use some of the "early" integrated level techniques to gradually move a patient towards the end of vision therapy and a future of binocular bliss. Most techniques that fit into this category are modifications to those earlier described.

1. Brock string activites are brought into the integrated level of therapy by introducing additional jump accommodative demand (lens flippers).

2. Loose prism facility jumpsare brought into the integrated level of therapy by introducing additional jump accommodative demand (lens flippers).

3. Vectograms (or Tranaglyphs) are brought into the integrated level by the introduction of additonal jump accommodative demand (lens flippers).

4. Eccentric circles are brought into the integrated level by the introduction of plus and minus lenses.

5. Another very advanced eccentric circle technique is to move the fused circle in a large arc. Therfore, chiascopic or orthopic fusion must be maintained as binocular smooth pursuit eyemovements are made.

1. What are the diagnostic findings expected on the following tests for the three types of vergence dysfunctions listed below:

True C. I. True C. E. Pseudo C.I.

a. VA's (dist and near)

b. fused cross cylinder

c. Binoc. +/- 2.00 facilities

d. NRA

e. PRA

2. Tell us a bit about the wonders of the Brock string. How does it monitor fusion? How does it monitor suppression? How does it monitor binocular posture? Give an example how the Brock string can be used at each of the three binocular skill levels that apply to vergence therapy.

1. 3.

2.

3. Both plus lenses and BO prism have the same effect on fusional vergence. They accomplish this, however, by different means. What is the mechanism behind the effects of BO prism? What is the mechanism behind the effects of plus lenses ?

4. Both minus lenses and BI prism have the same effect on fusional vergence. They accomplish this, however, by different means. What is the mechanism behind the effects of BI prism? What is the mechanism behind the effects of minus lenses ?