A CCOMMODA TION. 1037 



also observed no changes during accommodation in the images reflected 

 from the cornea. Later measurements with the ophthalmometer have 

 failed to show any change in the radius of curvature of the cornea. 



Intra-ocular pressure. The condition of intra-ocular pressure during 

 accommodation has been the subject of much difference of opinion. 

 According to one view, the pressure in the vitreous rises while 

 that of the aqueous falls during accommodation. This view is 

 based chiefly on cases described by Forster. 1 In cases in which the 

 anterior chamber had been opened, the cornea was noticed to flatten 

 during accommodation, pointing to lessened pressure within ; while, in a 

 case of perforation of the cornea, the aqueous filling the opening receded 

 during accommodation. In these cases the general intra-ocular tension 

 was abnormally lowered, and it is doubtful whether the same phenomena 

 would occur in the normal eye, and this doubt is increased by the fact 

 that Forster notes that they occurred after the use of atropin. Mano- 

 metrical observations, however, in both cavities of the eyeball during 

 accommodation have failed to show any noticeable difference, 2 while it 

 has been found that injection of fluid into one cavity raises the pressure 

 of both equally. The free mobility of the lens during strong accom- 

 modation, described by Hess, would be impossible if there were any 

 difference of pressure in front of and behind the suspensory ligament. 



Hensen and Voelckers 3 found that in animals an artificial protrusion 

 of the vitreous through a puncture increased during accommodation. 



Nervous mechanism. The chief point of interest is the sup- 

 posed function of the sympathetic as the nerve of accommodation for 

 far vision. Jessop 4 observed recession of the anterior lens surface 

 on stimulating the long ciliary nerves, after the ciliary muscle had been 

 moderately contracted by pilocarpin. Morat and Doyon 5 assert that 

 when the sympathetic is stimulated in a dog or cat, under the influence 

 of morphia or pilocarpin, the anterior lens image enlarges, and that a 

 needle placed against the anterior lens surface indicates flattening of 

 the lens. They ascribed this effect to the inhibitory influence of the 

 sympathetic on the ciliary muscle. On the other hand, Langley and 

 Anderson 6 failed to observe either movement of the choroid, backward 

 movement of the anterior lens surface, enlargement of lens images, or 

 increase of distance between them. Heese 7 also failed to obtain any 

 separation of the lens images on stimulation of the sympathetic. In 

 the cat, with which animal Morat and Doyon obtained their most 

 marked results, Heese noticed a diffused halo round the lens image, 

 which he ascribed to dispersion rendered more obvious by the dilatation of 

 the pupil, and supposed that this may have misled the French observers. 



Unequal and meridional accommodation. By the former term is 

 meant accommodation of a different amount in the two eyes; by the 

 latter, of a different amount in the two meridians of the same (astigmatic) eye. 

 Observations of Hering and Donders are generally held to have disproved the 

 existence of the former, but A. E. Fick 8 has recently attempted to show that 



1 Kim. MonatsU.f. Augenh., 1864, Bd. ii. S. 368. 



2 For recent confirmation of this, see a paper by Hess, Arch. f. Ophth., 1898, Bd. xlvi. 

 S. 243. 



3 Centralblf. d. med. Wissensch., Berlin, 1866, S. 721. 



4 Ophth. Rev., London, 1887, vol. vi. p. 163. 



5 Arch, dephysiol. norm, etpath., Paris, 1891, Se"r. 5, tome iii. p. 507. 



6 Journ. Physiol., Cambridge and London, 1892, vol. xiii. p. 583. 



7 Arch.f. d. ges. Physiol., Bonn, 1892, Bd. Iii. S. 563. 



8 Arch. Ophth., N.Y., 1889, vol. xviii. p. 292. 



