Report of the Committee on Colour-Vision. 311 



The Scotoma has usually an oval shape, the long axis being 

 horizontal; it includes the macula and extends as far as the 

 optic disc. 



" Persons who suffer in this way are usually what would be 

 called heavy smokers, and they usually use strong tobacco. In 

 a large proportion of cases there has been some mental shock or 

 depression as an additional cause. The patient may have been a 

 heavy smoker for many years without apparent injury ; then his 

 wife or child dies, or he loses money or employment ; sleep and 

 appetite fail, his strength is reduced, and within a few weeks the 

 tobacco begins to take effect. 



" Entire disuse of tobacco usually effects a great improvement 

 of vision in a month or two, or even sooner ; complete recovery 

 is not uncommon. I do not know that tobacco amblyopia is 

 commoner in seaport towns than in Birmingham. Many sailors 

 smoke heavily, but their out-door life would probably render 

 them less liable than the less robust inhabitants of manufacturing 

 towns. 



" In relation to the present enquiry, tobacco amblyopia is pro- 

 bably the most important form of acquired colour defect, for it 

 comes on insidiously, without known cause, without pain, and 

 without other sign of illness ; it affects both eyes, and it does 

 not prevent the man from doing rough labouring work. The 

 patients who come to us are often still occupied in rough work ; 

 a clerk affected in like manner is quite unable to follow his 

 occupation. 



"Tobacco amblyopia would prevent a man from recognising 

 the colour of a distant lamp. Possibly he might recognise it by 

 viewing it indirectly, that is eccentrically, but as a matter of fact 

 I think that such a man would always look directly at the lamp, 

 if he could still see it at all, and would therefore fail to recognise 

 its colour. On the other hand he would recognise the colours of 

 large surfaces, for the retinal pictures of these would extend 

 beyond the scotoma. I think he would recognise the colours of 

 skeins of wool, such as are used in testing the colour sense. 



"Persons suffering from tobacco amblyopia complain of bad 

 sight; they never complain of being unable to see colours properly; 

 they are seldom aware that they have lost the power of seeing 

 the colour of small objects, until the fact is pointed out to them. 



"Peripheral and Eccentric Defects of Colour-sense are common. 

 They are present whenever the field of vision is contracted. They 

 may co-exist with normal vision for form and colour at the centre 

 of the retina, but in many cases central vision is impaired also. 

 Wherever the defect be situated, the colour-sense and the form- 

 sense are impaired simultaneously, but the sense of colour is lost 

 before the sense of form. Green is said to be lost first of all ; 

 certainly green and red are lost before yellow and blue. 



" Neurasthenic Amblyopia is one of the conditions in which the 

 visual field contracts, and the colour-sense is impaired or lost. It 

 occurs in persons suffering from nerve-exhaustion, hysteria, reflex 

 disturbances, shock, &c. 



VOL. LI. T 



