°All values represent differences between initial and subsequent baseline tests.

b Asthenopia measured in ordinal (rated) units. Higher scores represent fewer or less severe symptoms.

* Indicates statistically significant changes between baseline, control, and experimental testing.

change in curve type’° during the experiment; all patients tested were type 1 except for patient 5 whose curve was a type 2. Pretest and post experimental fixation disparity magnitude was similar in all patients except patient 6, who showed less eso disparity by casual observation after the experimental phase. Similarly, pretest and post experimental associated phoria magnitude showed little change except for patient 2 who demonstrated less base-in prism requirement after the experimental phase. In general, baseline tests revealed a slight eso-associated phoria, steep slopes at the zero prism diopter level, and low base-out ranges. After the experimental phase, base-out ranges increased significantly (t = 3.76, dF = 6, p < 0.01) from a baseline mean of 15.14 pd (SD = 6.49) to a post experimental mean of 30.86 (SD = 13.71). Mean value of base-in ranges (13.71 pd, SD = 3.90), associated phorias (4.71 base-out, SD =

4.64), and the magnitude of fixation disparity (0.86 min arc eso, SD = 4.30) were not significantly different from those measured during baseline testing. Although the slope at the 0 pd point did not show a consistent change, a flattening of the base-out portion of the fixation disparity curve was noted after experimental training in patients 2, 3, 4, and 6.

There was a close relation between changes in the forced-vergence fixation disparity curves and symptoms. In five of the six patients, the base-out range increased concurrently with the reduction in symptoms. In patient 1, overall shape and base-out range appeared to normalize during the control phase with concomitant reduction in symptoms. In patient 5, there was an increase in both postcontrol fixation disparity magnitude and symptoms.

DISCUSSION

The primary purpose of this study was to determine the effect of fusional vergence train-

ing under controlled conditions on the reduction of asthenopia in patients with convergence insufficiency. It is clear from our results that after RDS base-out training, there was a significant reduction in asthenopia. In addition, RDS convergence ranges improved significantly and base-out vergence performance using vectographic targets likewise increased. However, vectographic performance after experimental and control conditions did not differ significantly, and positive transfer from RDS vergence training to vectographic testing was less than that found in normal subjects.9 The reduced ability to transfer vergence skills learned in one task to another in our convergence insufficiency samples may explain why the asthenopia in many patients with convergence insufficiency is not relieved by doing only pencil pushup exercises. The patient with convergence insufficiency, unlike normal patients, may require practice involving several methods of vergence stimulation before becoming able to transfer these newly acquired skills from the clinic to the home and work environment. This hypothesis is supported by the finding that traditional orthoptics resulted in a further improvement of vergence skills and a further decrease in symptoms in the six patients. These six patients were dismissed with a mean asthenopia score of 30.5, which approaches the symptom-free level.

Changes in convergence performance were much smaller after the control phase in which there was no change in vergence demand. This supports the conclusion that improvements during the experimental phase were the result of more than the mere exposure to fusional targets. However, fusional vergence training alone significantly reduces symptoms in patients with convergence insufficiency. Additionally, the lack of changes in symptoms after the control phase strongly suggests that the symptoms were due to a vergence anomaly and not to psychosomatic or neurotic factors as suggested by others.2’ 19-21

The forced-vergence fixation disparity curves provided a useful comparison to other test findings. There was close correspondence between certain changes in the fixation disparity curves and patient symptoms. Thus, this curve may prove to be a useful indicator of patient symptoms. Indeed, concomitant changes in the curve and the symptoms were consistent with an earlier report.22 Contrary to others,23’24 we did not find a change in the slope of the curve at 0 after our experimental training phase. However, our training was limited to development of specific base-out fusional ability on RDS, and did not include the usual full repertoire of vergence and accommodation exercises4’8”7

The postexperimental increases in base-out fusional ranges on the fixation disparity curves