REGION OF THE EYE. 77 



Hemorrhage. Hemorrhage into the orbit may occur either as the result of 

 direct traumatism involving the contents, or from fracture of the base of the skull 

 through the orbital plate. The blood pushes its way anteriorly and shows itself 

 under the conjunctiva surrounding the cornea. It is prevented from appearing 

 on the lids by the orbitotarsal ligament. A subconjunctival hemorrhage alone is not 

 sufficient to justify a diagnosis of fracture of the base of the skull, although it is 

 a significant confirmatory symptom. 



Kronlein's Operation. In order to gain access to the back part of the orbit 

 to remove tumors, Kronlein resects the outer wall, divides the periosteum and 

 external rectus muscle, and so gains access to the retrobulbar space. The various 

 steps of the operation are shown in Figs. 90, 91, 92. 



THE EYEBALL AND OPTIC NERVE. 



The eyeball has three main coats, viz. : a fibrous outer coat, called the sclerotic; 

 a vascular middle coat, the choroid; and a nervous inner coat, the retina. 



Sclerotic Coat. The sclerotic coat forms a firm protective covering or case 

 for the delicate retina within. It is continuous posteriorly with the fibrous coat or 

 dura of the optic nerve, which is a continuation of the dura mater of the brain. At 

 the optic foramen, the dura mater splits into two layers; the outer layer forms the 

 periosteum, while the inner forms the dural coat of the optic nerve. This nerve also, 

 like the brain, has an arachnoid and a pial membrane. The sclerotic coat is con- 

 tinued forward over the front of the eye as the cornea. As it is essentially a mem- 

 brane intended to be protective in its function, its diseases are those of weakness: 

 thus, if the cornea is affected, it bulges forward and is called an anterior staphyloma ; 

 if the posterior part is affected, the sclera is stretched, and it forms a posterior 

 staphyloma. 



Anterior staphyloma may occur either rapidly as a small local protrusion, resulting 

 from ulceration of the cornea or a wound, or it may be slow in forming, and involve 

 nearly or quite the whole of the cornea, pushing it forward in the shape of a cone; 

 this is called conical cornea. Posterior staphyloma occurs in near-sighted people, the 

 anteroposterior diameter of the eye being longer than normal. If this posterior 

 staphyloma or stretching of the eye becomes marked, the choroid atrophies and the 

 functions of the retina are lost. The white sclera is seen with the ophthalmoscope, 

 surrounding or to one side of the optic nerve. 



Although the cornea has no blood-vessels, it still, from its exposed position, 

 becomes inflamed (keratitis) and ulcerated, and eventually blood-vessels may de- 

 velop into it from its periphery, constituting the disease known as pannus. 



The weakest portion of the globe is at the junction of the sclerotic coat with the 

 cornea. It is here that the sclera is thinnest. On this account, blows on the eye 

 cause it to rupture usually at this point, the tear encircling the edge of the cornea 

 for a variable distance (usually at its upper and inner quadrant) according to the 

 force and direction of the injury. On healing, a staphyloma may form at this point. 



The choroid or vascular coat of the eye contains the pigment or color of the 

 eye. It is continued forward as the ciliary body (or processes) and iris. Being a 

 vascular tissue, its diseases are inflammatory. If the choroid is affected we have 

 choroiditis ; if the ciliary region is inflamed, it is called cyclitis ; and if the iris is 

 inflamed we have iritis. 



The retina or nervous coat of the eye is concerned in the function of sight and 

 it, like other nerves, may be affected with inflammation, called retinitis. Sometimes 

 it becomes loosened from the choroid beneath by a hemorrhage or rapid stretching 

 of the sclera, constituting a detachment of the retina. Outside the disk is the macida 

 lutea and fovea centralis or region of distinct vision. 



Filling the interior of the eye is the jelly-like transparent vitreous Immor, enclosed 

 in the hyaloid -membrane. In front of the vitreous humor is the lens ; and the clear, 

 limpid liquid between the anterior surface of the lens and the posterior surface of the 

 cornea is the aqiieous humor. 



The lens, immediately behind the iris, is suspended in its capsule from the 

 ciliary processes by its suspensory ligament or zone of Zinn. Between the ciliary 

 processes and the sclera lies the ciliary muscle, which regulates the accommodation 



