ENTOPTICS. REVERSED IMAGES. 



161 



rays form with those from the other becomes more or less 

 open. 



Ent optics. The eye perceives not only external objects, but 

 certain details of its internal organization. 

 This portion of the visual phenomena is 

 called interior vision, or entoptics. A 

 bruise of the cornea through the lids, or a 

 scar or foreign body on its surface, the 

 vascular ramifications of the retina, and 

 other causes of that nature, sometimes 

 throw images on the retina of different 

 forms, such as striae, spots, globules, dark 

 or luminous circles which appear to move 

 in the eye. Certain of these images are 

 called ilies, or motes (musccR voliiantes\ 

 because they traverse the field of vision 

 from one side to the other. Their ap- 

 pearance results from nothing abnormal, 

 and they cannot be confounded, when 

 there is no other disturbance of the visual 

 functions, with the analogous signs which 

 accompany and denote some diseases of 

 the eye and brain. A. lateral movement 

 of the eye is sufficient to displace them or 

 cause them to disappear. 



Reversed images. The eye may be 

 compared to an optical instrument known 

 as the camera obscura. It is well known 

 that the image of objects appears re- 

 versed on the screen of the camera; in 

 the same manner the luminous rays which 

 spring from every point of an object at 

 which we look, traverse the cornea, the 

 aqueous humor, the crystalline, and the Fig. 3 6. 



vitreous body, in order to reach the re- 

 tina ; and are refracted in this transit, so that the image which 

 they form appears reversed at the bottom of the eye. In 

 examining the eye of an ox, of which the sclerotic has been 

 previously made thin or the eyes of albinoes, such as white 



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