REGION OF THE EYE. 79 



The aqueous humor does not dissolve the opaque lens after the age of thirty- five 

 years. Senile cataract rarely occurs before the forty-fifth year, so there is a period 

 of ten years in which a cataract may be a nuclear cataract without being senile. 



To remove a nuclear or a senile cataract, a slit is made through the cornea near 

 its scleral junction, a piece of the iris may (or may not) be removed, the anterior 

 capsule is cut with a cystotome and the opaque lens pressed out through the 

 opening so made, then through the pupil (either artificial or dilated with atropine), 

 and finally through the sclerocorneal incision. The posterior capsule is not injured, 

 and it prevents the vitreous humor from escaping. If inflammation follows the 

 operation, the iris and ciliary region throw out lymph and the remains of the 

 capsule become opaque, forming a secondary or capsular cataract. This is removed 

 by tearing or cutting it across with needles or extremely fine scissors. 



Iris. The iris is the continuation of the choroid through the ciliary body, and 

 extends down to the pupil, its free edge resting on the anterior surface of the lens. 

 The iris is composed of a vascular and fibrous anterior portion, and a muscular and 

 pigmented posterior portion. In consequence of its vascularity, the iris is the fre- 

 quent site of inflammation. When inflamed it pours out lymph which may cause it 

 to adhere to the lens behind, forming a posterior synechia. An anterior synechia is 

 where, on account of a perforation of the cornea, the iris washes forward and becomes 

 attached to the cornea in front. 



The circular muscle fibres surrounding the pupil are anterior, and form the 

 sphincter pupilltz muscle ; it contracts the pupil. The radiating muscular fibres, 

 which lie posteriorly, form the dilator pupilltz ; it dilates the pupil. The dark pig- 

 ment layer is on the posterior surface of the iris, and after an attack of iritis, as the 

 adherent iris is torn loose from the lens, it leaves patches of pigment adhering to the 

 anterior capsule. 



The iris, as it rests at its pupillary margin on the lens, divides the space anterior 

 to the lens into two parts. The part between the posterior surface of the iris and the 

 anterior surface of the lens forms the posterior chamber. The anterior chamber lies 

 between the anterior surface of the iris and the posterior surface (Descemet's mem- 

 brane) of the cornea. The two chambers communicate through the pupil. The 

 anterior surface of the iris toward its periphery is of the nature of a coarse mesh- 

 work, the spaces of which are the spaces of Fontana. They communicate with a 

 venous or lymph canal which passes around the eye at the sclerocorneal junction 

 {canal of Schlemm^). 



Aqueous Humor and Anterior Lymph Circulation. The aqueous humor 

 is of the nature of lymph. It is secreted by the ciliary processes and posterior surface 

 of the iris. It passes through the pupil to the anterior chamber, and enters the 

 spaces of Fontana to empty into the canal of Schlemm. The canal of Schlemm 

 empties its contents into the anterior ciliary veins. In iritis and glaucoma the lymph- 

 current is seriously interfered with. In iritis, the swelling and outpouring of lymph 

 blocks the spaces of Fontana and prevents a free exit of the aqueous humor from 

 the anterior chamber, therefore in this condition the anterior chamber is deep, and 

 the iris is seen to lie far beneath the cornea. 



Glaucoma. Glaucoma is a disease accompanied by increased intra-ocular 

 tension. The eyeball feels hard to the touch. It is supposed to be due to disease 

 of the ciliary region interfering with the canal of Schlemm and obstructing it. 

 Therefore, the drainage of the eye and the circulation of the aqueous humor is inter- 

 fered with. In iritis the anterior chamber becomes deeper, but in glaucoma, as the 

 intra-ocular tension increases, it pushes the lens forward, and it is seen to lie close 

 up to the cornea; so that a shallow anterior chamber causes the ophthalmologist to 

 suspect glaucoma and a deep anterior chamber iritis. The increased pressure within 

 the eye pushes the optic nerve backward at its point of entrance, so that it is seen 

 sunk below the surface of the adjoining retina, forming a distinct cup-shaped cavity 

 or pit. This is cupping of the disk. 



Optic Nerve. The optic nerve reaches from the optic chiasm to the eyeball, a 

 distance of about 5 cm. ( 2 in. ) . It enters the apex of the orbit through the optic foramen 

 at the upper inner angle, in company with the ophthalmic artery. The artery crosses 

 the under surface of the nerve from its inner to its outer side. The optic nerve has 



