4 AMES, PROCTOR AND AMES. 



picture. Most of the data has been published in a paper by Mr. 

 Ames and Dr. C. A. Proctor, entitled "Dioptrics of the Eye." 2 



It is the purpose of the present paper to convey as clear an under- 

 standing as possible of the nature of the retinal picture and to point 

 out conclusions to which such an understanding leads us. 



PREFACE. 



A consideration of the analogy between our eye and a photographic 

 camera is helpful for a general understanding of the subject. 



Broadly speaking the eye is like a camera, or more truly speaking 

 cameras were made like the eye, the lens of the camera corresponding 

 to the lens of the eye and the plate or film to the retina. As the 

 character of a photograph depends upon the kind of lens and plate 

 used, so the characteristics of our retinal picture depend first upon the 

 nature of the lens of the eye and second upon the nature and sensi- 

 tivity of the nerve structure, i.e., the retina upon which the image is 

 formed. 



Certain photographic lenses are corrected. 3 The detail in photo- 

 graphs taken with such lenses is clear and distinct over the entire 

 picture and free from distortion. Other photographic lenses which are 

 not corrected produce pictures in which the detail is indistinct and 

 distorted in varying degrees. 



The lens system of the eye is not corrected. The details in part of 

 the image formed by it are clear, in other parts unclear and all more or 

 less distorted. 



Furthermore, the retina, instead of being equally sensitive over its 

 entire area as is a photographic plate, varies in sensitiveness in differ- 

 ent parts. 



As a result of the effects of the lens system of the eye and the effects 

 of the variable sensitivity of the retina the retinal picture has charac- 

 teristics which make it markedly different from photographs taken 



2 Journal Opt. Soc. of Amer., Vol. V, Jan. 1921. 



3 The image of a scene formed bv a simple lens (called uncorrected), such as 

 a spectacle lens or a magnifying glass, is not an exact reproduction of the scene 

 itself. The detail of objects at the center of the picture is slightly softened and 

 has chromatic edges. The detail at the sides of the picture is still more softened 

 and objects at the side are bent and distorted. 



To make the detail at the center as well as at the sides perfectly sharp and 

 to do away with distortion, so called corrected lenses were devised. Ihey 

 consist of a combination of two or more simple lenses of determined character 

 and separation. 



