member of a pair was then randomly assigned to either an experimental or control group. Patients in the experimental group initially received a vergence training procedure identical to that experienced during RDS baseline testing. Training consisted of 100 trials per weekly session. At the end of each session, maximum convergence attained before the onset of diplopia was recorded. The vectograms were then separated in a base-out direction until diplopia occurred, and the value was recorded. Patients in the control condition received the same number of RDS stimulus presentations as their matched partners. The convergence demand, however, in the control group remained constant (i.e., the right and left views were superimposed at 40 cm). When a patient in the experimental condition attained either a minimum of 25 of positive relative convergence during three successive sessions or completed 15 sessions, that patient and his matched control partner reversed conditions. The new experimental group received vergence training until the previously stated criteria were met, whereas the new control group received an identical number of trials and sessions without programmed changes in vergence demand.

After this second phase, RDS baseline testing was again performed, and traditional orthoptic therapy was initiated. This included various accommodative.’6”7 vergence, and stereoscopic training procedures.4’8 After a minimum of eight sessions, one per week of orthoptics, a final RDS baseline evaluation was conducted along with measurements of asthenopia and fixation disparity curves.

Different experimenters performed various clinical and experimental procedures throughout this study without having access to patient performance during other segments, so as to minimize experimenter bias. All findings were kept confidential until termination of the experiment and all testing was standardized.

RESULTS

Vergence performance and asthenopia scores for each patient during baseline, control, experimental, and orthoptic therapy phases are presented in Fig. 1. Performance during RDS testing and training represents maximum vergence achieved in prism diopters, while vectographic scores represent the break point in prism diopters using base-out fusional stimuli. Asthenopia scores represents the total of the patient’s score on a questionnaire, with higher scores representing fewer and/or less severe symptoms.

It is evident that after the experimental phase

(automated vergence training) all patients exhibited significant increases in maximum vergence as compared to that recorded in the preceding baseline or control phase. Mean increase in vergence for all seven patients was 17.7 (SD = 6.9). In contrast, a much smaller vergence increase was noted after the control phase; mean increase in convergence was only 2.4 (SD = 4.1) (Table 1). Statistical analysis revealed that maximum vergence scores in baseline, control, and experimental phases were significantly different (F = 7.75; DF = 2,12; p > 0.01). Increases in vergence ranges for vectographic testing followed a similar pattern, with larger increases following the experimental phase (mean increase = 5.57 pd SD = 6.68) than the control phase (mean increase = 2.14 pd, SD 3.48). These differences approached, but failed to reach, statistical significance (F = 3.35; dF = 2,12; p < 0.10). After orthroptic therapy administered to five of these patients, retesting of vergence ranges using vectographic stimuli was completed. Findings indicated a moderate, but variable, improvement in base-out break point in comparison to that found at the end of the experimental phase (mean improvement = 7.30 pd, SD = 13.39).

Fig. 1 also shows each patient’s asthenopia score after baseline control and experimental phases. A Friedman two-way analysis of variance’8 revealed a statistically significant difference in reported symptoms between these conditions (X2 = 8; dF = 2; P = 0.016). As expected, larger changes occurred after the experimental phase (mean decrease in symptoms = 6.42; SD = 3.46) than the control phase (mean decrease in symptoms = 0.43; SD = 4.76). Further decreases in symptoms occurred after orthoptic therapy in the four patients for whom data were available (mean decrease in symptoms from a mean baseline finding of 20 to the end of orthoptics was 10.5 in these four patients (a classification shift from “moderately uncomfortable” to “very comfortable”). The final asthenopic score (mean = 30.5; SD = 3.30) was close to the upper limit of 35 which represents a totally asymptomatic patient, thus indicating in our small sample that orthoptic therapy significantly reduced asthenopia.

Forced vergence fixation disparity curves for six of the seven patients are presented in Fig. 2. Each graph contains baseline and postexperimental test curves, with five also showing postcontrol test curves. Our forced-vergence fixation disparity data for six patients were analyzed with respect to curve type, curve range, curve slope, magnitude of fixation disparity, and magnitude of associated phoria. There was no