This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
The sensitiveness of the eye to impressions is increased by strychnine, the field of vision becoming larger, and the sight more acute, so that objects can be distinctly observed at a greater distance, and the field of colour is increased for blue. This action appears to be to a certain extent local, as it occurs more distinctly on that side where the strychnine has been injected hypodermically. The sense of colour is affected in a remarkable way by santonin, which at first causes objects to appear somewhat violet and afterwards of a greenish-yellow. The yellow colour has been ascribed to staining of the media of the eye by santonin, as it becomes yellow when exposed to the light; others again have supposed the alteration in the apparent colour of objects to be due, first to a stimulation, and then to a paralysis of those constituents of the retina by which the violet colour is perceived.
1 Engelmann (and von Genderen Stort), Pfuger's Archiv, xxxv. p. 498.
2 Gradenigo, jun., Allg. Wiener med. Ztg., 1885, No. 29.
The sensibility of the eye for red and green appears to be sometimes diminished by physostigmine.