ACCOMMODATION. 1035 



ciliary muscle before it affects the iris, and applied eserin after using 

 homatropin. The normal eye showed similar marked shaking, the 

 observation being especially striking when opacities of the lens existed. 

 The shaking was also observed subjectively. On moving the head from 

 side to side, and then stopping the movement, an observed needle 

 appeared to make three or four oscillations after cessation of movement 

 of the head. The same phenomenon was observed in entoptic observa- 

 tion of the lens. The mobility of the lens during marked accom- 

 modation, produced voluntarily or by means of eserin, was ascribed by 

 Hess to slackening of the suspensory ligament. Hess x also confirmed 

 Tscherning's observation of a downward movement of the lens during 

 accommodation, but found further that the direction of the movement 

 depended on the position of the head, and that the movement did not 

 occur when the head was inclined so that the iris was horizontal, 

 showing that it was due to gravity. The movement of the lens was 

 determined by the apparent movement of a point of light which moved 

 with the head, and had a constant position relative to the eye ; during 

 strong accommodation there was an apparent rise of the point of light, 

 showing a downward movement of the retinal point stimulated. The 

 amount of movement of the lens, with strong voluntary accommodation, 

 was found to be about '3 mm., while in the eserinised eye, on moving the 

 head from shoulder to shoulder through an angle of 180°, the displace- 

 ment of the lens amounted to 1 mm. 



Hess also found a certain amount of mobility in the antero-posterior 

 direction, and investigated its amount by determining the near point 

 with the head inclined forwards and backwards. With voluntary 

 accommodation he found in several individuals that in the two posi- 

 tions of the head, the near point varied to an extent corresponding 

 to a difference of refraction of "34 D to -48 D, and calculated that this 

 corresponded to a displacement of the lens antero-posteriorly of 15 

 to -21 mm. With the eye well under the influence of eserin, the refrac- 

 tion, as shown by the near point, changed to the extent of -61 to \S1 D, 

 showing a displacement of the lens of -26 to *36 mm. With relaxed 

 accommodation no change in the near point with altered position of the 

 head could be observed. Hess suggests that the previous observations of 

 recession of the posterior lens surface may have been due to the position 

 of the head. 



Crzellitzer 2 has confirmed the observations as to the shaking of the 

 lens, but supposes that this is due to a muscular tremor and not to 

 slackness of the zonula. This explanation cannot, however, apply to 

 the other observations of Hess. 



Several observers have noted irregularities of the border of the lens 

 in albinos and in cases of absent iris, such as might be due to greater 

 pressure on certain parts than on others. Hess 3 observed that this 

 appearance, which he describes in most cases as a wavy border, becomes 

 quite uniform after the instillation of eserin. When the lens is ob- 

 served from in front in similar cases, its outer zone is seen as a circular 

 band, bright by reflected, dark by transmitted light. This appearance 

 is due to total reflection, and has been used as an indication of change 

 of shape of the lens. The breadth of the border depends on the angle 

 at which the two lens surfaces meet, increased breadth showing increased 



1 Areh.f. Ophth., 1897, Bd. xliii. S. 477. - Loc. cit., S. 90. 



3 Arch. f. Ophth., 1896, Bd. xlii. Abth. 1, S. 288. 



