54 

 PERIODIC OPTHALMIA— MOONBLTNDNESS. 



This is an eye disease peculiar to horses and mules. Be- 

 fore the development of veterinary science the belief was 

 prevalent that the moon exerted a direct or indirect influence 

 upon the eyes; because the inflammatory attacks recurred at 

 monthly or somewhat regular periods. Thus the names 

 "moon blindness" and "mooneyed horses" originated. But 

 as veterinary science progressed, extensive clinical and anat- 

 omical investigations made known the fact that moonblind- 

 ness was a periodic or rpicurring inflammatory disease of the 

 entire eye, involving primarily the iris, the choroid coat and 

 the ciliary bodies. 



Symptoms. — This disease makes its appearance very sud- 

 denly — generally beginning in the night; in the morning 

 the eye is found closed, extremely sensitive to light with a 

 very great flow of tears down over the cheek. In some in- 

 stances there is systemic fever, while in other milder cases, 

 it is not manifest: but, as a rule, the horse or m\i\e is dull, 

 wanting in vigor, and energy, indicating constitutional dis- 

 turbance. The eye ball is drawn backward into the orbital 

 cavity, by the retractor muscle ; this makes it appear smaller 

 than the healthy eye ; after several attacks the eye ball is said 

 to shrink in size — decrease in actual volume. The conjunc- 

 tiva exhibits slight swelling and diffuse reddening ; the surface 



Fig. 16. 

 Diffuse cloudiness of the cornea as observed in moon blindness and 

 in inflammation of the cornea. The internal structures of the eye 

 are cut off from view by the total opacity of the cornea (after 

 Armatage). 



