On the strength of this method of inquiry there is a prevalence of opinion that the asthenopic disorders common in myopia are caused by over-exertion of the ocular muscles; indeed people believe this so strongly that they assume the presence of muscular asthenopia even in individuals in whom the habit of working with relative divergence is already firmly rooted. Relative divergence may perchance cause annoyance through double images, though this really seldom happens, but it can never cause muscular asthenopia, for the internal recti muscles protect themselves by means of relative divergence from any stronger exertion. Asthenopic disturbances are certainly frequent in myopia, but the above method of inquiry does not at all prove that their cause lies in the ocular muscles, for those appearances from which one concludes dynamic relative divergence and muscular asthenopia, are found in almost all myopes, even when the latter have no asthenopic troubles, for they owe their origin to the nature of the myopia. Myopes learn to converge to the distance of their far point, without exerting the accommodation; if we now cause a point at this distance to be fixed and then exclude one eye, or make binocular fusion impossible by means of vertical prisms, what imaginable reason is there for the excluded eye to remain in proper fixation? In emmetropia the habitual relation between accommodation and convergence will be able to ensure that the excluded eye also remains covering the fixed object, convergently as well as accommodatively; in myopia, every discretionary relative divergence up to parallelism of the lines of vision is perfectly justified, because no effort of the accommodation takes place. How in the world can it be held to be pathological that a movement of convergence does not occur, when one has just artificially removed all those physiological conditions which could possibly have brought it about? If one now likes, as v. Graefe proposes, to determine the prisms, which can be overcome by means of the outward movement, there is no doubt about the fact, that with the aid of prisms the lines of vision may be made parallel or even divergent, the retinal images indeed, always retaining the same distinctness, in so far as they are not injured by the prismatic diffusion of colours. There is just as little reason why the convergence usually attainable should not also be restored by the aid of prisms with the bases outwards, the retinal images are not only impaired by the prisms, but the accommodation united with the convergence, no longer corresponds to the real distance of the fixed point. Enough, all these incidents, which are to prove the presence of muscular asthenopia in myopia, occur when the investigation is carried out as usual in the region of the far point, entirely on a physiological basis, and must not therefore be held to be pathological without further proof.