io 3 6 VISION. 



thickness of the lens. The border becomes broader during accommo- 

 dation, and it is said that the lens can also be observed to diminish 

 in size concentrically. 1 



Changes in suspensory apparatus.— The free mobility of the 

 lens, and the changes observed in the regularity of its edge, are 

 evidence that the suspensory ligament is slack during accommodation. 

 In cases of absent iris, a fine radially striated appearance may be 

 observed in the position of the ligament, and Hess found that this 

 striation became indistinct after the use of eserin. In animals, Hensen 

 and Voelckers 2 found that a style placed behind the ligament showed 

 that it became slack during accommodation. Schon 3 has objected that 

 this is only true of the fold of the ligament which runs to the posterior 

 surface of the lens, which he supposes to become bent on itself, while the 

 anterior stronger process remains tense. 



The behaviour of the ciliary processes during accommodation has 

 been much discussed. When observed from in front in albinos and in 

 cases of absent iris, Becker 4 noted recession in near vision, but most 

 other observers have seen the processes move forwards, and at the same 

 time approach the optic axis. They are also said to swell slightly. 

 When observed in animals through a window in the sclerotic, the 

 ciliary region is seen to sink inwards during accommodation (Hensen 

 and Voelckers). 2 The space seen between the ciliary processes and the 

 edge of the lens appears to remain approximately constant during 

 accommodation (Hjort, 5 Hess). 



Hensen and Voelckers 6 found that during accommodation the choroid 

 moved forwards. They obtained this result in an extirpated human eye 

 as well as in animals. They found that a needle showed a movement of 

 the choroid, amounting to \ mm. at the equator of the eyeball, diminishing 

 from this point, so that no movement was observed in the ciliary and 

 macular regions. The retina moved with the choroid. The circular or 

 oval phosphene, seen on sudden relaxation of an accommodative effort 

 in the dark, has been ascribed to the movement of the choroid. It is 

 probably due to traction near the posterior pole of the eyeball, for 

 Berlin 7 found that, when produced simultaneously with an ordinary 

 pressure phosphene, the latter appeared outside the ring of the accom- 

 modation phosphene. 



In addition to the associated contraction of the pupil during 

 accommodation, the iris is pushed forwards by the bulging lens. If 

 the eyeball is observed laterally, the pupillary edge may be seen to 

 move forwards while the peripheral zone recedes. Helmholtz 8 found 

 the amount of movement forwards about '4 mm. 



Tscherning 9 observed a greater recession of the middle than of the 

 outermost zone of the iris, but other observers have failed to confirm this. 



Thomas Young 10 found that his range of accommodation was as great 

 when his cornea was covered with water as under normal conditions, and 



1 Graefe u. Saemisch, "Handbuch d. ges. Augenh.," Bd. vi. S. 470. 



''Experimentaluntersuch. tiber d. Mechanismus d. Ace," Kiel, 1868. 



Arch./, d. ges. Physiol., Bonn, 1895, Bd. lix. S. 448. 



Med. Jahrb., Wien, 1863 (2), Bd. xix. S. 159. 



■ hhn. Monatsbl.f, Augenh., 1876, Bd. xiv. S. 205. 



I Arch. f. Ophth., 1873, Bd. xix. Abth. 1, S. 156. 



7 Ibid., 1874, Bd. xx. Abth. 1, S. 89. 



* "Handbuch d. physiol. Optik," 2te Aufl., S. 141. 



m tJ C , „ physwl norm - et Vnth., Paris, 1894, tome vi. p. 40. 

 ™ Phil. Trans., London, 1801, p. 57. 



