DEPARTMENT OF SURGERY. 
545 
All abscesses should be opened and thoroughly cleaned, if 
necessary they may be scraped or curetted. When a clean 
healthy surface is obtained, the wound is treated as a surgical 
wound, and unless a large area is involved, it will heal very 
readily if it is not located in the cornea. 
IV. Fistula may result from various causes, usually, how¬ 
ever, from traumatic or surgical wounds. Perforating wounds 
that open the anterior chamber are often very troublesome ; 
intraocular pressure drives the aqueous humor through the 
opening, and prevents union by first intention. Paracentesis of 
anterior chamber sometimes causes open wounds, which do not 
heal very readily. Cysts in the coats of the eyeball occasionally 
open into the anterior chamber and allow the aqueous humor 
to be forced through the fistula, causing an enlargement or sac 
or bulging of the conjunctiva ( chemosis pallida). The treat¬ 
ment of ocular fistula is sometimes a very simple procedure ; it 
depends much upon the nature of the wounds ; if infected, it must 
be made aseptic, and when this is accomplished, the intraocular 
pressure must be removed by paracentesis of the anterior cham¬ 
ber ; if the wound has been made aseptic, it will unite before 
the anterior chamber is refilled. 
V. Ulcers on the antro-external surface of the eyeball 
are very common conditions ; they may be simple, traumatic, 
and toxic. Ulcers are generally located in the cornea, and may be 
sthenic or asthenic, especially when due to infection; occasion¬ 
ally some of them are very obstinate, and do not yield to treat¬ 
ment, but keep spreading in all directions ( serpiginous ) from 
the sclero-corneal margin ; when they involve the deeper struc¬ 
tures, they are named rodent ulcers ; these sometimes cause 
perforations. Ulcers in the conjunctiva or sclera are generally 
due to trauma, and are more satisfactorily treated than those of 
the cornea. Corneal ulcers are sometimes very difficult to de¬ 
tect, especially when they result from vesicular keratitis; these 
vesicles often rupture and leave large epithelial denudations, 
which, in the early stage, can scarcely be discovered without 
the use of fluorescin. In serpiginous ulcers ( creeping ulcers ) 
the destruction of tissue may extend until it involves the entire 
anterior surface, and leaving nothing but Descemefs membrane ; 
and, when this is perforated, the aqueous humor escapes and the 
iris falls against the posterior wall of the cornea, which closes 
the opening ; in the course of time the iris adheres to the wall 
(< anterior synechia') and the anterior chamber refills. When the 
opening is very large we may have prolapsus of the iris. The 
