CATARACT. 103 



consist in an effusion of lymph into the posterior chamber of the 

 eye, against or upon the anterior surface of the capsule of the lens. 



A Capsulo-lenticular Cataract is one of a mixed charac- 

 ter, in which lens and capsule, and, necessarily, liquor Morgagni 

 too, are all involved in opacit}*. 



Another Distinction of- Cataracts arises out of the nature 

 of their composition or consistence. Commonly, a cataract is firm 

 or hard; at least, in most cases acquires consistence by age, 

 though when first -formed it may be of a soft nature — caseous, as 

 sometimes it is called. D'Arboval speaks of a fluid cataract, one 

 that from its whiteness often acquires the name of milky : I have- 

 no recollection of ever having seen one myself of this description. 

 To these may be added, the osseous cataract ; of which Mr. Charles 

 Percivall, V.S., Royal Artillery, has a fine specimen in his mu- 

 seum. This appears to be the ultimate change the lens under- 

 goes, and one that is the result of many years' continuance of the 

 cataract*. 



Cataracts differ also in Colour or Shade. — Their colour 

 not only depends upon their nature or consistence, but likewise 

 upon the stage of formation they happen to be in, as well as upon 

 their age or continuance. After attacks of ophthalmia, we behold 

 the pupil changing from its natural clear dark blue, and acquiring 

 a greyish or greenish tint, or, while contracted, having a dusky or 

 blackish blue aspect; eventually dilating and clearing again, to 

 assume the last change — that of cataract. 



The Cause of Cataract, speaking generally, in ninety cases 

 out of a hundred probably, is periodic ophthalmia. One attack 



* Examples of the same are recorded in human medicine. Mr. Wardrop, 

 " in one case, besides the capsule of the lens being ossified, found several 

 large but thin scales of bony matter dispersed throughout the vitreous 

 humour, which in all probability were ossifications of the hyaloid membrane." 

 The capsule has oftener been detected osseous than the lens itself But in 

 an eye sent to Mr. Wardrop by Mr. A. Burns, the central portion of the lens 

 was converted into hard bone ; the only instance Mr. W. ever met with in 

 which ossification of the lens was unattended by ossification of the capsule. 

 Dr. Mackenzie informs us, that a lens dislocated into the anterior chamber, 

 in consequence of a blow on the eye, is very apt to become ossified. — MaC' 

 kenzie on the Diseases of the Eye. 



