A qualitative model of an autonomic effector control loop is presented, showing the components of information transmission. With reference to the pupil-light reflex and accommodation it is argued that injection of drugs such as pilocarpine forms an input to the forward loop of the system, whereas drugs such as DFP and cycloplegics cause a change in gain. In these terms their effect on accomodative-convergence may be understood. Competition between certain miotic drugs as well as dose-response non-linearity is explained by reference to the model. It is proposed that under some conditions, properties of the open-loop system are responsible for denervation-sensitization.
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