Changes in Pupil Dynamics at High Altitude—An Observational Study Using a Handheld Pupillometer

Abstract

Gross pupil dynamics are used as an indirect measure of brain function. Changes in hypoxia and intracranial pressure are thought to alter pupil responses to light. This study assessed a portable handheld pupil measuring device (pupillometer) in the field investigating the changes in pupil size, speed of reaction, and rate of constriction/dilatation with hypoxia induced by changes in altitude. A correlation between pupil dynamics and acute mountain sickness was sought. Seventeen volunteers were studied following acute exposure to 3450 m and then during a trek to 4770 m in Ladakh, India. The pupillometer was used to record maximum and minimum pupil diameter in response to a standard light source with calculation of latency, constriction and dilatation velocities. Acute mountain sickness (AMS) was recorded using Lake Louise self completed questionnaires both in the morning and afternoon on each day. Acute altitude exposure resulted in a significant reduction of percentage change in pupil size (36.5% to 24.1% p=<0.001), significant delay in pupillary contraction (latency; 0.208 to 0.223 seconds p=0.015) and a significant slowing of the rate of contraction (constriction velocity; -2.77 mm/s to -1.75 mm/s p=0.012). These changes reverted to normal during a period of acclimatization. A significant diurnal variation in pupil size was also observed. There was no significant difference between subjects with and without AMS. The handheld pupillometer is a suitable robust tool for monitoring changes in pupil dynamics in the field. With acute exposure to hypobaric hypoxia associated with an ascent to a moderate altitude, there is a general slowing of pupil function which reverts to normal within a few days of acclimatization. There appears to be a marked diurnal variation in pupil size. The measurements clearly demonstrated an effect of hypoxia on cerebral function, but these changes did not relate to moderate AMS.

Diurnal Rhythms of Spherical Refractive Error, Optical Axial Length, and Power in the Chick

“…5a). This diurnal variation agrees with that found in humans 20 but not with randomly occurring pupil diameter acrophases 40 or maximum pupil size in the dark in other species. 26,41 There does not appear to be a contribution from differential accommodation as pupil size is not correlated with MOR.…”

“…In humans, circadian fluctuations have been reported in intraocular pressure (IOP, see Sit 7 for review), axial length, [8][9][10] choroidal thickness, 8,11 anterior chamber depth, 8,10,12 corneal topography, [13][14][15] optical aberrations, [15][16][17][18] pupil diameter, 19,20 and corneal thickness. 8,10,13,21 In marmoset, a primate myopia model, circadian rhythms of IOP, axial length (cornea to sclera), and choroidal thickness have been observed.…”

Pupil Dynamics in Hypoxic Conditions: Caudwell Xtreme Everest Results

“…We previously reported a reduction in pupil aperture change (PAC) and constriction velocity (CV) within 1 hour of arrival at high altitude (3450 m and 4770 m), with these changes reverting to normal over subsequent days (Wilson et al, 2008). We here extend these observations as part of the Caudwell Xtreme Everest expedition (ascent profile and methodology as previously described (Levett et al, 2010).…”

Acute Hypoxic Hypoxia and Isocapnic Hypoxia Effects on Oculometric Features

“…Pupillary dynamics ( 29 ), eye movements (i.e., fi xations and saccades) ( 15 ), and blink metrics ( 30 ) have all been linked to cognitive activity. Changes in these parameters have been reported in hypoxia and altitude acclimatization ( 6 , 26 , 29 ) and, therefore, might have a promising role in extreme and highly demanding environments such as aviation and mountaineering.…”