Eleven esophoric individuals underwent a one month base-in training program. The program was successful in expanding the limits of most subjects' base-in limit. This is contrary to most literature which report the base-in limit to be very difficult, if not impossible to move.
Calculated proximal convergence/nearness ratios, unexpectedly showed esophores to exhibit a positive proximal vergence response, prior to training. Contrary to the order reported in other studies, we found the greatest proximal response to be at the base-in limit, least at the base-out limit, and intermediate at the phoria. Furthermore, there was a reversal noted post-training; the maximal response occurred at the base-out limit, followed by the phoria, and base-in limit, respectively.
It was concluded that a proximal effect can be partially attributed to the increase in the base-in vergence range, i. e., by enhancing the "awareness of farness", or disenhancing the awareness of nearness . But also implied in the findings is a relation between fusional convergence and proximal convergence. We concluded that as the base-in vergence limit increased, the need for proximal converence lessened, so the PC/D ratio decreased .
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