| Nurses are affected by the arduous requirements of shiftwork. Countermeasures to ease this difficult burden would aid in the recruitment and retention of nurses and improve the quality of patient care. One area which holds promise is exploration of mechanisms which control human circadian rhythms.; The body clock is thought to be located in the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN, through the sympathetic nervous system, stimulates the pineal gland to synthesize melatonin (a hormone marker of circadian phase state). Apparently, overlapping neuronal fields in the superior cervical ganglion supply both the pineal and the eye through the carotid sympathetic nerve branch. Pupil diameter is determined by the antagonist action of sympathetic and parasympathetic input to the intrinsic muscles of the iris. Smooth muscle control of palpebral fissure is essentially controlled by the sympathetic system.; Subjects were measured every 30 minutes over 24 hours to observe bilateral changes in pupil size and palpebral fissure. Measurements were made by infrared videography recordings and the Fitness Impairment Tester{dollar}sp{lcub}TM{rcub}{dollar}, a binocular pupillary camera recording system. Twelve males and 12 females (ages 18-29 years, {dollar}rmbar x{dollar} = 21.6) were studied around the clock while they remained within a light controlled facility ({dollar}<{dollar}100 Lux).; The acrophases (maximums) for pupil diameters and palpebral fissure distances were estimated using a cosine curve fitting technique applied to each 24-hour data set. Pupil diameter acrophases occurred randomly throughout the day. Rayleigh test for these data produced r = 0.016, p {dollar}>{dollar} 0.900 (not significant) for pupil diameter, therefore, no circadian rhythm was detected. The data demonstrated a significant circadian rhythm for both resting and maximum palpebral fissure values. However, palpebral fissure acrophases were widely distributed with the largest portion of the peaks occurring between 10AM and 10PM. Sample mean vectors were at 5:37PM for resting (95% C.I. = 3:04PM-8:08PM) and 4:44PM for maximum (95% C.I. = 1:44PM-7:44PM). The Rayleigh test for these data produced r = 0.440, p = 0.008 for resting values and r = 0.403, p = 0.020 for maximum opening values.; The data did not support the hypotheses that sympathetic innervation to the pineal is found in the eye, and results do not demonstrate any applicability of human eye measurements as circadian markers. |
