CHAPTER VI 



PHOTOMECHANICAL RESPONSES IN 

 THE RETINA 



One of the most fascinating yet most perplexing problems 

 in retinal biology pertains to certain structural changes which 

 the retina exhibits in response to illumination of the eye. 

 The chief changes which occur are: 1) movements of the 

 pigment in the epithelial pigment cells, 2) changes in the 

 form and length of the visual cells, and 3) changes in the form 

 and staining reactions of the retinal nuclear layers. 



Until 1915 to 1916 the extensive investigations on this 

 phase of retinal physiology were confined almost exclusively 

 to European workers, and an excellent compilation of the 

 work was published in 1907 by Garten. In 1915 Arey pub- 

 lished an historical survey of the results in this field — the 

 first of its kind in the English language, and he himself sub- 

 sequently contributed extensively to our knowledge of these 

 changes, particularly in fishes and amphibia (1916a, 19166, 

 1919). The author investigated the problems in the eyes of 

 reptiles (Detwiler, 1916, 1920, 1923a, 1923c) and in certain 

 nocturnal mammals (1924). 



Pigment. Variations in the degree to which retinal pigment 

 extends down between the visual cells was noted as early as 

 1856 by H. Miiller. Morano (1872) also noted the incon- 

 stancy of epithelial pigment distribution. It seems, however, 

 that the first observations regarding the effect of light upon 

 the retinal pigment were recorded by Czerny (1867), who 

 found that after light stimulation the pigment epithelium 

 and the retina were less easily separated. But to Boll (1877) 

 and Klihne (1877), working independently, is given the credit 

 for the discovery of pigment migration. They found that in 

 the light, the retinal pigment of the frog extended nearly 



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