in alternate ocular occlusion. The viewing targets presented during the on cycle were 6/7.5 (20/25) visual stimuli. Both the control and the experimen.tal patients received experience in identical telebinoculars, with identical viewing stimuli, during the same session time and day.

The experimental group had a plus lens placed in front of the right eye and a minus lens in front of the left eye during alternating monocular accommodative training. During the on cy cle the patient was required to clear the lens interposed between the eye and the 6/7.5 (20/ 25) visual stimuli. After 5 min, the plus and minus lenses were switched. If the patient was able to maintain clarity for 5 min with plus and minus lenses, without any signs of ocular fatigue, the power of the next pair of lenses was increased. In addition, the patient had to demonstrate instantaneous accommodative changes. However, if the patient could clear one lens but not the other, only the lens cleared was increased according to the following sequence:

+0.50/—0.50; +0.75/—1.00; +1.00/—2.00; +1.25/

—3.00; +1.50/—4.00; +1.75/—4.50; +2.00/—5.00; +2.25/—5.50; +2.50/—6.00 D. By the end of twelve 30-mm sessions, all patients were expected to clear a +2.50/—6.00 D within 2 s without any signs of fatigue. The final value represented 8.50 D accommodative change.

The matched control subjects underwent the same training as the experimental subjects with one exception. During each of the twelve 30-mm training sessions (2 times per week for 6 weeks), the accommodative lenses marked with plus and minus values (e.g., +0.50/-0.50) were actually piano lenses. Neither the patient nor the therapist was made aware of this fact. Thus, during training, control patients experienced no altered accommodative demand. At the end of 12 sessions, both the experimental and control groups once again underwent accommodative testing, vergence testing, and the asthenopia rating questionnaire.

After this testing, the experimental patients received an additional 6 weeks of training identical to that of the control group, i.e., all training was now with plano lenses. The control group patients also received another 12 weeks of training. The conditions were identical to those of the original experimental group so that training was performed with lenses having different values of accommodative demand (e.g., +0.5/—0.5). This matched-subjects crossover design was used to control primarily for “order of treatment effects” and to demonstrate that patients switched from piano to accommodative demand lenses would show corresponding changes in accommodative amplitude and in asthenopia. After this second 12-week period, both groups again received a third clinical testing and as-

thenopia questionnaire. Once again, all evaluations were done by clinicians having no know!edge of the patient’s ocular status or group, experimental or control.

RESULTS

Fig. 2 depicts the mean absolute values of accommodative amplitude during baseline, experimental, and control conditions as a function of the order of treatments. The abscissa depicts the three phases of testing, i.e., baseline, phase 1, and phase 2. Mean accommodative amplitude for all patients in each phase (determined by minus lens to blur) is plotted on the ordinate. The experimental and control groups performed similarly at the initial baseline, 5.25 and 5.08 D, respectively. However, patients who received experimental training during phase 1 showed a marked increase in accommodative amplitude compared to the control group. Amplitudes after phase 1 were 8.00 and 5.16 D, respectively. The latter value did not differ from its initial baseline measure. After phase 2, a substantial change in performance could be seen for the control group. Accommodative amplitude increased to 7.5 D for these patients, whereas it remained virtually unchanged for the original experimental group. When the data from all patients were combined so as to compare the change in accommodative amplitude after either experimental or control conditions, a statistically significant difference was observed (t = 7.36, dF = 4, p <0.01).

Table 1 presents changes in accommodative amplitude for each patient after exposure to plano lenses or accommodative demand lenses. The order of assignment to groups is also indicated. As is apparent, all but one patient showed an increase in accommodative amplitude after exposure to the experimental condition that was greater than that to the control condition. Table 1 also shows that the mean change of accommodative amplitude was significantly larger after experimental than control conditions.

Fig. 3 presents the mean absolute asthenopia scores for experimental and control groups during baseline, phase 1, and phase 2 conditions. Asthenopia scores are presented on the ordinate, whereas phases of testing are presented on the abscissa. The scores during initial baseline testing were somewhat lower for the experimental than for the control group patients, 6.0 and 8.67, respectively (the higher the score, the fewer the symptoms). After phase 1, patients who received experimental training showed a marked reduc tion in symptoms compared to the control group, 13.0 and 9.33, respectively. The control group showed only a small change from baseline find ings. After phase 2, when the original experi mental and control groups received the cross-