Authors Reply

The article is a reply to comments by G.K. Hung (see ibid., p.2787-9, 2010). We emphasize that the primary purpose of the study was to determine if the two most commonly cited dynamic models of accommodation and vergence predicted two empirical findings taken from our investigation of near addition lenses. Our empirical investigation measured vergence adaptation and a concurrent reduction of CA associated with that process. Two commonly cited models of vergence and accommodation correctly predicted the change in vergence adaptation. Only one model (C.M. Schor, 1992) predicted the concurrent reduction in CA with vergence adaptation. In his letter, Dr. Hung uses a static model to compare the steady-state CA responses of the two models, which was NOT the intention of the study. We would argue that the framework of model discussion must be those, which are dynamic, and hence quantitatively describe the replacement of fast vergence with that of slow or tonic responses. Static models are not appropriate as vergence adaptation is not described in that format.