766 



metre angle aiul dioptric the same, then this line divides tiie right 

 angle between ordinate and abscis exactly in two equal parts. This 

 line, which unites all the points denoting an equal number of 

 metreangles for convergence as dioptries for accommodation, is 

 called: "Donders' Convergence-line". 



if the relation between accommodation and convergence was 

 absolute and unfringible, then a normal person would only be able 

 to see the |)oints of the convergence-line sharp and single at the 

 same time, and no other points; every person with an abnormal 

 refraction or a heteroplioria would not be able to see one single 

 point sharp and single at the .same time. 



Luckily the connection between accommodation and convergence 

 is more or less a loose one, so that at every convergence the 

 acommodation can, to a certain degree, be made stronger oi' slighter 

 than coincides with the degree of convergence. 



If one converges 6 metreangles, then an acconimodation of 6 

 dioptries coincides with (his, an accommodation, which one can raise f.i. 

 to 8 dioptries, or decrease to 3 dioptries. This interval between 3 and 

 8 dioptries is called the relative accommodation for a convergence 

 of 6 metreangles; the interval from 6 to 8 dioptries is called the 

 positive, from 6 to 3 dioptries the negative relative amplitude of 

 accommodation. 



The relative amplitude of accommodation differs a great deal in 

 each individual case and can be increased to a certain degree by 

 long practice. It is not necessary that the negative and positive part 

 of the relative accommodation are alike. 



One can determine the relative accommodation for all points in 

 the area of manifest contraction of the ciliary muscle and connect 

 the relative near and far points to gel the line.s of the relative near 

 and for points. 



Accoi'ding to Hess the relative accommodation is the same at 

 every convergence, so that for every normal person the linos of the 

 relative near and relative far points run parallel to Dondkhs' Con- 

 vergence-line. (See fig. 1 : pq and R.S.) 



Hkss is of opinion that one can continue these lines in the area 

 of latent ciliary muscle contraction, but could not prove this, as no 

 measuring could be done in the "latent" area. 



The next question theiefore is: 



f. How do the lines of the relative near and far points run in 

 the area of latent ciliary muscle contraction "r 



Our reasoning is as follows: if the supposed individual of tig. 1 

 converges 6 metreangles, the unparalysed ciliary muscle can contract 



