Fig. 2. Total divergence fusional

reserve (phoria/tropia plus divergence

fusional convergence amplitude mea-

surements minus prism in the specta-

cles) is presented for each orthoptic

therapy session. Measurements are for

disparity stimuli moving with a con-

stant velocity (ramp) which is depict-

ed in the upper curve, and jump duc-

tion (step) which is depicted in the

lower curve. As amplitudes improv-

ed, therapy was increased in difficulty

by making the vergence stimuli smal-

ler and by increasing the velocity of

the target during ramp therapy.

continued to improve, additional step-wise reductions in the total amount of

prism correction were made, i.e., 30B0, 25B0, 2oBO, i6BO, I2BO, ioBO,

and 8B0. Initial prismatic changes were large, while subsequent changes

were made progressively smaller. With progress, fusional amplitude therapy

was made more difficult by slowly increasing the velocity of the vergence

stimuli to 5k/sec and/or by reducing the stimulus size to 6 degrees.’2

As smooth divergence amplitudes improved, more difficult step (jump

duction) stimuli were then introduced. Stimulus presentation, vergence de-

mand, and reinforcement contingencies were presented with the VTS3 com-

puterized method of training. Fig. 2 presents both the maximum total fu-

sional divergence reserve and maximum total step amplitude measured at

each session. It is readily apparent that both ramp and step fusional ampli-

tudes progressively improved over time.

Over a one-year period of weekly therapy, horizontal divergence fusional

amplitudes improved at distance to x/- I0/- 14 and at near to x/4/2; the more

positive post-therapy values demonstrated moderate improvement of fusion

ability. Initial occlusion with an alternate cover test resulted in an esophoric

deviation of approximately 7^ at distance and orthophoria at near. Upon pro-

longed repeated alternate cover testing for two minutes, the magnitude of the

deviation gradually increased, until it equalled the magnitude found at the

initial examination, i.e., 40^ esotropia. Three years after orthoptic treatment,

the patient is presently wearing progressive addition lenses without any

prism incorporated into the spectacle lens before each eye. After a stressful

day, however, the patient often has to revert to his prismatic glasses, which

have 2^ BO in each eye.

Towards the end of the orthoptic therapy, both horizontal versional (mon-

ocular and binocular) and vergence eye movements were recorded using a

commercially-available infrared eye movement system (Gulf and Western,

Eye Trac Model 200). This system has a bandwidth from DC to 250 Hz, a

resolution of 0.2 degrees, and a linear range of +/- 10 degrees; however, the

frequency response of the eye movement traces was limited by the band-

width of the strip chart recorder (DC to 8o Hz). The target consisted of a

small (5 mi arc), bright spot of light presented on a display monitor 57 cm

from the subject which was controlled by a function generator.

Representative eye movement recordings are shown in Fig. 3. Midline

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J.Cooper et al.