Saccadic velocity and pupillary reflexes during acclimatization to altitude (4300 m)

Introduction: Oculometrics have been shown to be responsive to acute hypoxemia. We investigated whether oculometrics could be used as an objective index of a hypoxic effect on the central nervous system (CNS) during altitude acclimatization. We hypothesized that oculomotor reflexes [pupil diameter (PD), constriction amplitude (CA), constriction latency (CL), and saccadic velocity (SV)] changed in concert with a select number of accepted acclimatization variables and that these changes correlated with the severity of acute mountain sickness (AMS). Methods: After sea-level, baseline (SLB) measurements were obtained, 18 men (19-33 yr) were transported to Pikes Peak, CO (4300 m), where they remained for 14 d. Periodic measurements (days 1-4, 6, 7, 9, 10, and 12) were made of PD, CA, CL, and SV in addition to heart rate (HR), pulse oximetry (SpO₂), end-tidal PO₂ and PCO₂, 24-h urinary catecholamine concentrations, and AMS severity (environmental symptoms questionnaire, ESQ). Results: PD and CL decreased from SLB on days 1-4 and subsequently returned toward SLB; these changes paralleled changes in ventilatory and circulatory variables. CA decreased on days 1 and 2 and remained decreased for 12 d. SV increased over days 1-6 then returned toward SLB with continued exposure, similar to changes in urinary catecholamines. With acclimatization, CL correlated with HR and SpO₂; SV correlated with PCO₂, HR, and SpO₂. AMS severity peaked during days 2-4, returned toward SLB over the next 10 d, and correlated only with CL (p = 0.045). Conclusions: Oculometrics can be used as an indicator of CNS hypoxia and altitude acclimatization, although there was no strong correlation with AMS severity.