PROLAPSE OF THE EYEBALL 425 



Amaurosis. Black Cataract. — Under this title we class all of those 

 morbid states where there is partial (amblyopia) or complete loss of 

 eyesight or blindness (amaurosis) without any change in the external 

 portion of the eye. In the majority of cases it is due to pathological 

 process in the retina or the optic nerve, namely retinal hemorrhage, 

 separation of the retina, papillitis, retinitis, or atrophy of the optic nerve. 

 In rare instances it is due to direct pressure of hemorrhages on the optic 

 nerve, or to inflammations to neof ormations in the orbit, or at the entrance 

 of the optic nerve, or it may be due to certain lesions in the cranial 

 cavity, such as inflammation, hemorrhage, tumors, parasites, which are 

 located in the base of the brain near the optic centre. Certain poisons 

 have a specific effect on the optic nerves and cause permanent or tem- 

 porary blindness such as nicotine, salicylic acid, extract of male fern, 

 santonin, carbon dioxide, or decayed meat toxines. The sight is some- 

 times affected by sporting dogs working in the field when it is covered 

 with snow. Congenital amaurosis cannot be said to be extremely rare, 

 it being rather common in toy terriers and particularly so in Boston 

 terriers. 



Symptoms. — "When a dog is blind in both eyes it is not difficult to 

 determine the condition, on observing the careful method of walking, 

 the absence of fright when menaced with a stick or hand, and the very 

 much increased use of the sense of smell, or of hitting obstacles or 

 walking into them, and, in addition, the fixed, stary look, and the dilata- 

 tion of the pupils which do not contract in the presence of strong light. 

 Cases have been observed where there was pronounced amaurosis and 

 W'hile the pupil was ordinarily dilated, when the animal was brought 

 into strong light the pupil contracted. Where there is partial or com- 

 plete loss of sight in only one eye, it is more difficult to determine the 

 condition. Blind one eye w'ith some dark material and try to see 

 whether the pupil dilates and contracts with the light. A peculiar form 

 of blindness is hemeralopia (night blindness) , In such animals the sight 

 is perfectly good in the day, but at night the sight is partially lost and 

 the animal has no confidence in walking about. This condition is found 

 to be due to a peripheral opacity of the refractory mediums. The treat- 

 ment consists in the attempt to remove the exciting cause, if possible. 



Prolapse of the Eyeball. 



(Exophthalmus; Prolapsus Bulhi Oculi.) 



There are a number of causes that produce prolapse of the eyeball. 

 It may be crowded out of the cavity of the eye, or exposed in its external 

 circumference by the swollen and distended eyelids which are closely 

 adherent to its posterior surface (Fig. 149). This condition occurs 



