Pupil Dilation

Pupil size is assessed in both well and dimly lit settings. The pupils should remain symmetrical but should dilate when the lights are dimmed. A difference in pupil size is termed anisocoria. In a dimly lit room the pupils are best visualized with an ophthalmoscope providing ambient light. The pupils should each reach near maximal size.

​

​

​

​

​

The structures evaluated include the iris, the dilator papillae muscles and the sympathetic pathway innervating the dilator muscles. The diameter of the pupil results from a tonic balance between the parasympathetic and sympathetic innervation of the pupillary constrictors and dilators. In normal room light the pupils are not fully dilated or constricted but close to midrange. By removing the light source which stimulates the pupils via the pathways described for the PLR, the dominant pathway becomes sympathetic resulting in dilation. This pathway also becomes dominant during fear, anxiety or pain.

The structures evaluated include the iris, the dilator papillae muscles and the sympathetic pathway innervating the dilator muscles. The diameter of the pupil results from a tonic balance between the parasympathetic and sympathetic innervation of the pupillary constrictors and dilators. In normal room light the pupils are not fully dilated or constricted but close to midrange. By removing the light source which stimulates the pupils via the pathways described for the PLR, the dominant pathway becomes sympathetic resulting in dilation. This pathway also becomes dominant during fear, anxiety or pain.

The structures evaluated include the iris, the dilator papillae muscles and the sympathetic pathway innervating the dilator muscles. The diameter of the pupil results from a tonic balance between the parasympathetic and sympathetic innervation of the pupillary constrictors and dilators. In normal room light the pupils are not fully dilated or constricted but close to midrange. By removing the light source which stimulates the pupils via the pathways described for the PLR, the dominant pathway becomes sympathetic resulting in dilation. This pathway also becomes dominant during fear, anxiety or pain.