PCT is the time that pupil takes to constrict and dilate once, when stimulated with a slit beam of light (Daniel E and Rao PSS, 1995). Integrity of pupillary reflex pathway is required for this light reflex. Pharmacological studies have demonstrated that PCT is mainly determined by integrity of parasympathetic nerve supply to the iris (Martin CN and Ewing DJ, 1986). Incomplete atropinization produced prolongation of PCT, whereas sympathetic blockade by intraocular application of guanithidine did not produce any effect on PCT. Further, pupil cycling can be elicited even when sympathetic supply to the pupil is cut surgically, indicating the role of sympathetic efferent is uncertain on PCT (Milton JG et al. 1989).

test was performed at Ophthalmology Department of the Institute. It was assessed by measurement of PCT using Haagstreit-type of slit lamp (Martin CN and Ewing DJ, 1986). PCT was measured with the subject sitting at the slit lamp in a dimly lit room after dark adaptation for 15 minutes. A horizontal, 1-mm wide slit beam of moderate intensity light was focused through the slit lamp, accurately on the lower part of the iris, in a plane perpendicular to it. The beam of light was slowly elevated until it overlapped the margin of the pupil and initiated cycle of constriction and dilatation. The oscillatory cycles were timed for ninety cycles (three 30-cycle runs), and time taken for single cycle is calculated. In the current study, timing device was developed in our laboratory with greater accuracy. The stopwatch used, incorporated an oscillator of 1 KHz, which gave an accuracy of one millisecond. It was connected to a counter on which the number of cycles to be counted could be selected. The counter starts the stopwatch at the beginning and end of the pre-selected number of cycles, which reduces human error to a minimum. The stopwatch was calibrated on an oscilloscope. Count was performed in both right and left eyes. For the purpose of analysis only the longer cycle of the two estimates from each subject was considered (Cahill M et al. 2001). Cardiac parasympathetic tests were carried out in the Physiology laboratory of the Institute. Cardiac PNS activity was assessed using spectral analysis of Heart Rate Variability and conventional cardiac PNS tests which included heart rate responses to different maneuvers. To quantify HR, the analog ECG signal was recorded using lead II, to obtain a QRS complex of sufficient amplitude and stable baseline. ECG signals were conveyed through an A/D converter (Biopac MP 30, Biopac system Inc. Santa Barbara, CA) at a sampling frequency 500Hz to a PC and were analyzed off-line, after visual checking of abnormal ECG. Both HRV and conventional tests were performed to assess cardiac PNS activity. For HRV, HR variation during normal breathing for a period of 5 minutes was recorded, with subject supine, awake and resting. The data so gathered was subjected to spectral analysis.

Following the 5-minute resting period measurements for HRV, subjects underwent conventional cardiac PNS tests. The tests included timed deep breathing, effect of cough, immediate heart rate response to standing, maximum handgrip and Valsalva maneuver. The test results of HR based responses were expressed using heart rate differences (delta HR) for timed deep breathing, cough maneuver, and MHG, while RR interval ratio was used for immediate HR response to standing and Valsalva maneuver (Simonion SX and Herbison 1997; Wei JY, 1983).

Statistics

Statistical analysis was performed with an SPSS package (10.5). Normality of the distribution was assessed with the Kolmogorov Smirnov goodness of fit test. Data are expressed as mean ±SEM with 95% confidence interval. All the variables were compared between age and gender groups using Two-Way ANOVA, with the test for age and gender effects as well as their interaction. Looking for the overlap of the confidence interval, the

were ascertained using Pearson’s correlation. In all the instances null hypothesis was rejected at P<0.05.

compared the subjects of specific age groups which were belonging to a narrow age-range (Umetani K et al. 1998; Liao D et al. 1999; Kuo, TBJ 1995).

Therefore this study attempted to cover wider age range of both gender and stratified age wise classification was continuous where subjects were grouped into children, adolescents, adults and middle aged. Further, since nutritional status and the physical activity level are consider to be confounding factors in the measurement of autonomic nerve activity, in this study both these factors were controlled for different study groups.

In this study, it was found that there was a slower reaction time with lengthening of PCT with ageing. The significant increment in PCT observed in this study, between adolescents and adults as well as between adults and middle age group. Data also showed that increase in PCT was not significant between children and adolescents. A relatively small difference in the age range between children and adolescents may have contributed to lack of significant difference between these two study groups. Prolongation of PCT in relation to age observed in this study is in agreement with the results of previous studies (Patel AD 1999; Manor RS et al.1981; Sood AK et al. 1985). Miller et al. observed a significant difference of PCT in subject groups above and below 50 years; however, between 12 and 50 years there was no significant age trend (Miller SD and Thompson HS, 1978). Another study, demonstrated that PCT of 56-65 years age group is significantly prolonged in comparison to younger age group (Sood AK et al. 1985). It has been reported that 80 percent of the subjects in the age group of 10-49 years had PCT, which were less than 800 millisecond. Among the elderly, upper limit of normality was more than 1010 milliseconds (Manor RS et al.1981). It is found that there is a trend towards increase of 2-4 milliseconds per year in PCT (Miller SD and Thompson HS, 1978). Usually for an individual the PCT becomes shorter as pupil size is reduced (Cahill M, 2001). In addition,with ageing, pupil size decreases and therefore a decrease in PCT with age could be expected. However, the age effect found in this study as well as previous studies was an increase in PCT with ageing, which suggests that factors other than pupil size are responsible for the influence of age on PCT. It has been suggested that measurement of PCT is particularly sensitive to dysfunction in parasympathetic efferent limb of the pupillary light reflex arc (Martin CN and Ewing DJ 1986).

The association of pupillary abnormalities with autonomic and peripheral dysfunction in diabetes has been demonstrated previously using pupillographic techniques (Smith SE et al. 1978; Friedman SA, 1967). Earlier, diminished PNS input to the iris was observed by measuring the latency time for pupillary response to a light stimulus (Pfeifer MA 1982). Reduced iris PNS activity associated with ageing could be due to the decreased sensitivity of the Edinger-Westphal nucleus.

The gender related differences in cardiac-autonomic nervous system have been studied earlier (Liao D et al., 1995) .Few studies representing the influence of gender on PCT have shown that there is no sex difference in pupil cycle time (Smith SE et al. 1978; Cahill M, 2001). These reports are based small number of subjects, or restrict their population to certain age category. However, in this study also PCT, a measure of ocular PNS function did not differ between two genders.

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