Physiology. - "Determination of the Pomer of the Accommodation- 

 Muscle" . By Prof. J, v.AN uek Hoeve and H. J. Fliekinga. 



(Comniunicated at the meeting of September 29, 1923). 



The action of the accommodation muscle, the M. Ciliaris, makes 

 itself apparent to ns by tiie increase of refraction of the lens, the 

 so-called accomodation of llie eye. 



Tiiere are still many obscure points in the subject of accommo- 

 dation; for instance, it is still entirely unknown to us what relation 

 exists between the contraction of the acconimodation-niuscle and 

 the increase in refraction of the lens 



A few ophlhalmo-physiologisls are of opinion that contraction of 

 the accoMimodalion-muscle increases the tension in (he ligament of 

 the lens, the Zonula Zinii, while most of them assume, with Hm.mhoi.tz, 

 that contraction of the ciliary muscle causes a relaxation of the 

 Zonula Zinii, so that opportunity is given lo the lens to curve 

 according to its elasticity. When, through increase of age, the elasticity 

 disappears, contraction of the ciliary muscle does not assert itself 

 by increase of refraction of the lens. 



Even if one assumed the last theory, one meets with many unsolved 

 questions, e g. : 



a. Is the strongest possible contraction of the accommodation 

 muscle necessary to obtain the greatest possible accommodation? 

 DoNDKRS and Landoi.t assumed this and find still followers in these 

 days, amongst others Ct,arke and Duane. 



FucHs, Hkss and others, on the contrary, are of opinion that the 

 accommodation muscle can contract far more strongly than is necessary 

 to obtain a maximal accommodation. 



FucHs expresses this in the following way : (he accommodation- 

 muscle can first contract so far that the lens can follow its elasticity 

 completely, resulting in a maximal accommodation; the eye is then 

 focussed on a poirU, which is determined by a physical properly, 

 viz. the elasticity of the lens. FtiCHs therefore calls this point the 

 "physical near point". Now he muscles can contract considerably 

 more, so that the Zonula hangs entirely relaxed and the lens could 

 if only its elasticity were unlimited, increase its refraction consideiably, 

 allowing the eye to focus on a point, lying still closer by, and 



50* 



