216 THE ORGANS OF SPECIAL SENSE 



life, but, should it persist, it will give rise to one form of con- 

 genital cataract. When the lens is in its proper position, its 

 margins cannot be seen on ophthalmoscopic examination, 

 even when the pupil is as widely dilated as possible. The 

 observation of part of its margin shows that the lens is dis- 

 located or partially dislocated. This injury involves complete 

 or partial rupture of the suspensory ligament and, since it has 

 lost its attachments, the lens trembles visibly when the eye is 

 moved iridodonesis. 



The Posterior chamber of the eye is the small space which 

 intervenes between the peripheral part of the anterior surface 

 of the lens and the posterior aspect of the iris. It contains a 

 clear fluid, termed the aqueous humor ^ which is secreted by 

 the ciliary processes. Through the opening of the pupil the 

 aqueous humor of the posterior chamber communicates with 

 that in the anterior chamber, but, if this communication is 

 prevented by the formation of adhesions between the lens and 

 the iris, the fluid in the posterior chamber accumulates and 

 causes an increase in the intra-ocular tension. 



The Anterior chamber of the eye is bounded in front by the 

 cornea and behind by the anterior aspects of the iris and the 

 central portion of the lens. In the angle between the peri- 

 pheral margin of the iris and the cornea, the aqueous humor 

 drains away into the sinus venosus sclene (canal of Schlemm) 

 (p. 212), and, therefore, cases of glaucoma which are due to 

 obstruction of the normal communication between the anterior 

 and posterior chambers of the eye are readily cured by the 

 performance of iridectomy. 



On OPHTHALMOSCOPIC EXAMINATION, the red reaction of 

 the retina, which is caused by the great vascularity of the 

 chorioid and the corresponding opacity of the sclera, is at 

 once seen. The Porus Opticus (Optic Disc) can be found by 

 observing on the cornea the image of the lamp, utilised in the 

 examination. By manipulating his mirror, the observer can 

 cause the image to pass along the horizontal diameter of the 

 cornea, and, when the image reaches the junction of the middle 



