The short term effect of atlanto-axial high velocity low amplitude manipulation with cavitation on Edge Light Pupil Cycle Time

Abstract

Background Edge Light Pupil Cycle Time (ELPCT) is a measure of the pupillary light reflex mediated via the autonomic nervous system (ANS). ELPCT is a measurable constant, unaffected by eye measured (i.e. left versus right eye), gender, visual acuity, refractive error, eye colour and pupil size. Previous research suggests that spinal manipulation techniques can produce distant effects mediated in part by the ANS. Objective To investigate the immediate effects of atlanto-axial high velocity low amplitude manipulation on ELPCT. Design A three group randomised controlled study. Methods Thirty participants (mean age = 23.8) without eye, central or autonomic nervous system pathology had their ELPCT measured in both eyes pre- and post-manipulation. The manipulation technique used was a high velocity low amplitude (HVLA) rotatory thrust, with the applicator localised to the atlanto-axial joint on the left ( n = 10) or right ( n = 10) determined randomly. All HVLA manipulations were associated with audible cavitation. The control group ( n = 10) underwent the same protocol, including pre-positioning for the manipulation, but without the thrust. Results ELPCT measures demonstrated a significant decrease between groups ( P = 0.004) and between groups according to eye measured ( P = 0.022). Significant decreases between pre- and post-manipulation measures of ELPCT indicated an association between side manipulated and eyes, with right-sided manipulation producing a decrease in ELPCT in the right eye ( P = 0.001) and a left-sided manipulation producing a decrease in the left eye ( P = 0.013). No other significant changes were observed. Conclusion ELPCT, mediated via the ANS, is directly influenced by HVLA manipulation with cavitation to the atlanto-axial joint. The ANS changes observed in this study demonstrated a unilateral response to HVLA manipulation.