DISEASES OF THE EYES. 



PERIODIC OPHTHALMIA (MOON-BLINDNESS), 



Is a specific inflammation of most of the structures of 

 the eye. Relapses occur, lasting from 2 to 14 days. It 

 is dangerous, and is liable to be followed by a still more 

 dangerous disease — cataract. It is hereditary, but it may 

 be caused by rheumatic predisposition or blood contami- 

 nation, a bite or blow, foreign substances under the lid, 

 overwork, especially the young, filthy and badly ventilated 

 stables, the eruption of the tushes, compression of the 

 roots of the molar teeth on the fifth pair of nerves, work- 

 ing in coal-pits or other dark places, &c. 



Fig. 28. First appearance of 

 ° Periodic Ophthalmia. 



Fig. 29. Its termination. 



Symptoms.— First or inflammatory stage : Upper lid 

 droops; tears in superabundance; lids, venous vessels, 

 and conjunctive membrane swollen; the globe dull and 

 sunken; circumference of cornea sometimes exhibits a 

 broad, nebulous circle; front chamber, at first usually 

 clear, becomes so obscured that the pupil is hardly dis- 

 tinguishable ; the pupil is contracted and resembles the 



