88 The Eye 



The netves come from the lenticular ganglion (p. 58), bringing 

 motor influence from the third for the contraction of the pupil, and 

 from the sympathetic for its dilatation (p. 59). Thus, irritation of the 

 retina, the optic nerve, or the third nerve causes contraction of the 

 pupil, and of the cervical sympathetic, dilatation. 



Iritis. When the iris is inflamed its vessels are so engorged, and 

 its stroma is so infiltrated with effusion, that its bright colour is 

 changed to a rusty hue, and it is hindered in its work. Thus the pupil 

 but slowly contracts, even when a strong light is thrown upon the 

 retina. A pink circle appears just beyond the border of the cornea, 

 where the anterior ciliary arteries are bending inwards to the iris, and 

 are also anastomosing with the conjunctival vessels. This interesting 

 anastomosis is well shown in vol. ii. of ' Quain's Anatomy' (9th edition, 

 p. 403), by which it is easy to see that when the ciliary arteries are 

 engorged a ring of subconjunctival congestion is almost inevitable. 



So full are the vessels that serum escapes into the aqueous, and 

 lymph oozes from the vessels and glues the iris to the capsule of the 

 lens synechia posterior (awex*)*, holding together}. These adhesions 

 may be complete and permanent ; if, however, they be limited to certain 

 spots, and if, under the influence of atropine, the free part of the pupil- 

 lary border only be drawn away, the pupil becomes irregular. (The 

 atropine probably acts by paralysing the third nerve, and so allowing 

 the sympathetic filaments free play.) 



The treatment of iritis demands the immediate application of atro- 

 pine, so that the sticky border of the pupil may be kept from adher- 

 ing to the capsule of the lens ; or that, adhesions having formed, they 

 may, if possible, be stretched and broken. Leeches should be applied 

 to the temple to relieve the engorgement of the ophthalmic vessels. 

 And, if the tension and pain persist, the distended anterior chamber 

 may be treated as the inflamed pericardial lymph-space is treated in 

 pericarditis, namely, by paracentesis. 



When posterior synechia is permanent and universal, the aqueous 

 humour which is behind the iris can no longer flow through the pupil, 

 and, moreover, the iris itself is so disturbed by the attachment that 

 secondary attacks of inflammation are apt to recur (see GLAUCOMA 

 infra}. 



An artificial pupil is, therefore, needed : An incision is made 

 in the corneo-sclerotic margin (in the upper part, if possible, so that 

 the unsightly vertical pupil may be under cover of the lid), and the 

 pupillary border of the iris is gently dragged out of the wound by 

 delicate forceps which have been introduced into the anterior chamber ; 

 the piece of iris is then snipped off. 



The lens, biconvex, is suspended in the capsule, just in front of 

 the vitreous, and behind the iris. Indeed, when the pupil is con- 

 tracted a considerable extent of the iris is touching the lens, and 

 even pushed forwards by it ; but during dilatation of the pupil there is 



