Background: Evaluation of pupillary autonomic activity has clinical significance as pupillary autonomic dysfunction occurs earlier to cardiovascular autonomic damage. Pupil cycling is a feature of pupillary reflex arc and measurement of pupil cycle time is an index of Parasympathetic Nervous System (PNS) activity to the iris.

 Objectives: The present study aimed at establishing a reference value of pupil cycle time among healthy males and females between the age groups of 6-55 years and determine the influence of ageing and gender on pupillary autonomic activity and also correlating the same with cardiac autonomic activity.

Method: 252 healthy subjects, between the age group of 6-55 years were studied. Pupillary autonomic activity was assessed by measuring pupil cycle time. Cardiac PNS activity was assessed using spectral analysis of Heart Rate Variability (HRV) and conventional cardiac PNS tests

Result:  Mean pupil cycle time for children to middle age ranged from 818 to 958 milliseconds. It increased significantly (P=0.00) with ageing. No significant difference in pupil cycle time was found between males and females. The correlation of various cardiac PNS tests with pupil cycle time were statistically significant and negatively correlated ranging from 0.22 to 0.45.

Conclusion:  The study establishes reference value of pupil cycle time for males and females of age group between 6-55 years. The age related prolongation of pupil cycle time can be explained by diminished PNS to the iris with ageing as seen for cardiovascular system. The significant correlation obtained between pupil cycle time and various parameters of cardiac parasympathetic activity indicates that the measurement of pupil cycle time is as reliable and sensitive method as cardiac PNS tests to assess PNS activity.

Key words: Pupil cycle time; Reference value; pupillary autonomic activity; cardiac autonomic activity