gorham's pupil photometer. 



76: 



accommodation, a sensation of heaviness and coldness of the eyeball, enlargement of the 

 palpebral fissure, constriction of the small peripheral vessels, and slight lachrymation.] 



Myotics are those substances which contract the pupil : Physostigmin ( = Eserin, the alka- 

 loid of Calabar bean), nicotin, pilocarpin, muscarin, morphia, according to some observers 

 (Ghrunhagcn) cause stimulation of the oculomotorius, while others say they paralyse the sym- 

 pathetic. As these substances cause spasm of the ciliary muscle, it is supposed that the first of 

 these has an analogous action on the sphincter. It is probable that they paralyse the dilator 

 fibres and stimulate the oculomotor fibres. [Amongst local myotics, i. e. , those which act on 

 the eye, some act on the muscular fibres of the iris, e.g. , physostigmin or eserin, while others 

 act on the peripheral terminations of the 3rd nerve, e.g., pilocarpin, muscarin. Muscarin causes 

 very great contraction of the pupil from spasm of the circular fibres, due to its action on the 

 3rd nerve ; eserin, on the other hand, although contracting the pupil, also affects the dilator 

 fibres. The contraction of the pupil due to opium is central in its cause.] 



If the one pupil be contracted or dilated by these substances, the other pupil, conversely, is 

 dilated or contracted, owing to the change in the amount of light admitted into the eye into 

 which the poison has been introduced. The anaesthetics (ether, chloroform, alcohol, &c), 

 when they begin to cause stupor, contract the pupil, and when their action is intense they dilate 

 it {Dogiel). Chloroform, during the stage when it causes excitement (preceding the narcosis), 

 stimulates the centre for the dilatation of the pupil ; after a time this centre is paralysed, so 

 that the pupil no longer dilates on the application of external stimuli. Thereafter the pupillo- 

 constrictor centre is stimulated, whereby the pupil may be contracted to the size of a pin's 

 head ; ultimately this centre is paralysed, and the pupil becomes dilated. 



Time for Movements of Iris. The reflex dilatation of the pupil occurs slightly later than the 

 reflex contraction, the time in the two cases being 0*5 and 0*3 second respectively, after stimu- 

 lation by light {v. Vintsckgau). A certain time always elapses, until the iris, corresponding to 

 the strength of the stimulus of light exciting the retina, "adapts " itself to produce a suitable 

 size of the pupil {Aubert). Contraction of the pupil occurs very rapidly after stimulation of the 

 oculomotorius in birds ; in rabbits 0'89 second elapses after stimulation of the sympathetic, 

 until the dilatation begins (4tU). 



Excised Eye. Light causes contraction of the pupil in the excised eye of amphibians and 

 fishes {Arnold). Even the iris of the eel, when cut out and placed in normal saline solution, 

 contracts to light {Arnold), the green and blue rays being most active. Increase of the tempera- 

 ture causes mydriasis in the excised eye of the frog or eel, while cooling causes myosis {H. 

 Milller). 



[Size of the Pupil. Jonathan Hutchinson recommends a pupilometer, consisting of a metal 

 plate perforated with a series of holes of different sizes. The smallest hole measures about 3 of 

 a line, and the largest is 4^ lines. The plate is placed just below the patient's eye, and the 

 hole is selected which corresponds with the size of the pupil.] 



[Gorham's Pupil Photometer. This ingenious instrument may be used as a pupilometer, 

 and also as a photometer. It consists of a piece of bronzed tubing 1*9 in. long and 1*5 in. 

 diameter (figs. 545 and 546). One end is closed by a disc or cap, which is pierced in its radii by 



Fig. 545. Fig. 546. 



Gorham's pupil photometer. Fig. 545 shows the disc with a slot and two holes. Fig. 546 

 gives a side view with the diameter of the pupil marked on it. The upper end is closed by 

 the disc, while the lower end is open. 



a series of holes at distances varying from *05 in. to *28 in. There is a slot in the cap which 

 allows one pair of holes to be visible at a time, while on the cylinder is engraved the linear 

 distance of each pair of holes. In using the instrument as a pupilometer, look through the 

 open end of the tube (the bottom in fig. 546), with both eyes open, towards a sheet of white 

 paper or the sky, when two dies of light will be seen. Then revolve the lid or cap slowly until 

 the two white dies just touch one another at their edges. The decimal fraction opposite the two 



