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Manual of Veterinary Physiology. 



being thrown upon the retina fall in front of it, the rays 

 crossing and forming a diffused circle on the retina. If in 

 Fig. 31 the retina lies at (I— viz., the eyeball is too long— 

 the rays of light will focus in front of it and diverge at 

 " and h. 



Hypermetropia, or long sight, is due to the opposite con- 

 dition—viz., the eyeball being too short— whereby- the rays 

 of light are focussed behind the retina instead of on it. 

 The retina of a hypermetropic eye would be situated at 

 H (Fig. 31) ; the rays of light at c and/ have not yet come 

 to a focus. In this condition, by a great effort of accom- 



Fig. 31.- Diagram to illustrate Myopia \\i» Bypermetropia. 



G, the position of the retina in a myopic eye. a blurred image from 

 A B is perceived at e and o which are beyond the focus ; H. the 

 position of the retina in a hypermetropic eye. the image from 

 A B is blurred ate /, which are in front of the focus ; V. the 

 position of the retina in the emmetropic eye, the rays from A 1*. 

 are brought to an exact focus at </ A (Kirke). 



modation (a term which will be presently explained . the 

 divergent rays from a near object may be caused to focus 

 on the retina: the parallel rays from distant objects are 

 generally well seen without any great effort of accom- 

 modation. 



Since myopia and hypsrmetropia are due to the rays being 

 brought to a focus either in front of or behind the retina, 

 if we could supply horses with convex or concave spectacles, 

 their myopic or hypermetropic condition would bo of no 

 serious disadvantage. 



In the normal eye the retina must be situated the proper 



