A Case of Monochromatic Vision. 



179 



A Case of Monochromatic Vision." By Sir W. de W. Abney, 

 K.C.B., r.RS. Eeceived January 17, — Read Tebruary 1, 

 1900. 



Cases of monochromatic vision are rare, and I have thought it 

 right to put on record one which was kindly brought me some time 

 ago by Mr. Parker. The patient, whom we will call K. B., was aged 

 twenty-five at the time when I examined him for colour vision. The 

 notes of his case are as follows : — Vision always defective j has always 

 been colour blind. Has quick horizontal nystagmus ; probably an 

 absolute central scotoma. He is always " day blind." His vision for 

 right and left eyes is 6/60. He is not night blind. His fields are 

 nearly, but not quite, full for white. He shows no definite changes in 

 his eyes. 



I took his luminosity curve, and all colours he matched with white 

 with the same facility as if they were white. The following table 



Scale of 

 spectrum 

 (prismatic). 



K. B.'s 

 luminosity. 



P.'s 

 luminosity. 



Scale of 

 spectrum 

 (prismatic). 



K. B.'s 

 luminosity. 



P.'s 

 luminosity. 



56 



2-5 





32 



61-5 



65-0 



54 



9-0 





30 



43 -0 



50 -0 



52 



16-0 



7-0 



28 



37 -0 



36 -0 



50 



27 -5 



19-0 



26 



30 -0 



26-5 



48 



42-5 



39-0 



24 



34 '0 



19-5 



46 



61-0 



65-0 



22 



18-5 



14 -0 



44 



82 -5 



85 -0 



20 



14-5 



10-0 



42 



96-0 



98-0 



18 



11 -5 





40 



100 



99-0 



16 



9 



5-5 



38 



95 -5 



97-5 



14 



7-0 





36 



87-5 



90 



12 



5 





34 



75 -0 



80 -0 



10 



3-0 



2-5 



gives the luminosity of the spectrum to him, and for the convenience 

 of reference a previous case, which has already appeared in the ' Pro- 

 ceedings,* is given for comparison. In the accompanying diagram both 

 these curves are shown, together with the curve of luminosity for the 

 normal eye. As regards the first two, it will be seen that the maximum 

 of each curve is about scale number 40, or close to E. On the right- 

 hand side of the maximum the curves do not absolutely agree. K.B.'s 

 observations were first made in the red and green, and his readings 

 at first were not very close, and a mean had to be taken. As the 

 colours he had measured went towards the blue his measures were 

 much more accordant, as he had become accustomed to the methods 



