338 DISEA~SES OF THE EYES. 



apparatus differs from an ordinary photogi'aphio camera by, among other 

 things, the " stop " (the pupil) being in front of the lens, and by focussing 

 being performed by alteration being made in the shape of the lens by the 

 action of certain muscles. The choroid is dark-coloured, so as to enable it 

 to absorb any superfluous rays of light. The pupil has the power of con- 

 tracting and dilating in order to regulate the admittance of light. 



Simple Ophthalmia ( Conjunctivitis). 



This is inflammation of the membrane (tlie conjunctiva) whioli 

 covers the sm'face of the eye, and lines the eyelids. It may be 

 induced by mechanical injury or cold. 



When it is caused by a blow directly inflicted on the cornea, the 

 opacity will radiate from the point struck. This appearance, which 

 serves to distinp-uish the affection from that due to cold, will not 

 be present when the eye has been injured at a moment when it 

 was protected by the eyelid. In catarrh, both eyes are usually 

 afl'ected ; but in ophthalmia from injury, only one eye is as a rule 

 inflamed. The presence or absence of other signs of catan-h will 

 also help in obtaining a correct decision. In ophthalmia from a 

 blow, there will often be a mark of the injury on the skin of the 

 eyelid. Id catarrh ('' running ") of the eyes, the opacity com- 

 mences at the inner corner of the eye. 



SYMPTOMS. — The eye has the' appearance of having received a 

 blow. The eyelids are closed and swollen. The eyeball is drawn 

 back. Tears flow copiously. The haw projects ; and there is in- 

 tolerance of light. The conjunctiva is inflamed. The cornea grad- 

 ually becomes clouded by an opacity which appears to be super- 

 ficial and of a bluish colour ; characteristics which distinguish this 

 disease fi'om periodic ophthalmia (p. .339). 



TREATMENT.— Examine the part to see if there be any ex- 

 ternal injury. If a foreign body be found in the eye, remove it 

 carefully. To do this, and also to facilitate examination, it is -well 

 to produce insensibility of the part by applying to the surface of 

 the eyeball a few drops of a 5 per cent, solution of hydrochlorate 

 of cocaine (p. 619) in water, or it may be necessary to pull back 

 the haw by transfixing it with a needle and thread. Give a dose 

 of physic, and put the animal on laxative food. Foment the part 

 with warm water, and keep the horse in darkness. From time to 

 time smear the skin round the eyelids with extract of belladonna, 

 which can be made to adhere by mixing it with a little glycerine ; 

 or place in the eye a few drops ,of liquor atropinse sulphatis. The 

 belladonna, by virtue of its active principle, atropine, relieves the 

 congestion of the blood-vessels by causing their muscular coats to 



