The pupil as such is entirely dependent upon the function of the iris. Therefore, all reactions and conditions of the pupil are to be considered basically as no more than changes affecting the inner margin of the iris. For the irisdiagnostician, however, only those abnormal conditions are significant which by paralysis or irritation of the nerves controlling the muscles of the iris, produce changes in the function or state of the pupil. (M. sphincter pupillae = pupil contraction and M. dilatator pupillae = pupil dilation.) Consequently, all those disturbances which are caused by local injuries or other conditions of the eyeball are to be ignored.

The normal shape of the pupil is circular. It should lie in the centre of the iris (perhaps somewhat disposed towards the nasal side), and appear neither too large nor too small under ordinary conditions of lighting. The normal diameter is 3-4 mm. On the whole, relatively larger pupils are found in small children, while in adults the size of the pupil progressively diminishes as old age advances.

The pupil should not show any undue variation in width, and the movements of contraction and dilation should affect both pupils symmetrically.


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