Changes in chromatic pattern-onset VEP with full-body inversion

Intra-ocular pressure (IOP) increases to double that of its normal level under full-body inversion, in part simulating high IOPs found in glaucoma and ocular hypertension. Inversion also simulates negative g-forces experienced in aerobatic maneuvers such as those produced during aerial combat. Studies using achromatic pattern-reversal visual evoked potentials (VEPs) have shown losses in response amplitude when subjects are inverted and IOP is increased. In other studies, chromatic, pattern-onset VEPs have been shown to be a sensitive and objective indicator of ocular and systemic pathology. Thus, chromatic pattern-onset VEPs may also show changes in amplitude and/or latency when subjects are subjected to full-body inversion.

In this study we employed chromatic, pattern-onset VEPs to determine if there were changes in response latency for the different visual pathways with healthy subjects during full-body inversion. Stimuli were 1 cpd horizontal sine-wave patterns presented in an onset mode (100 ms on/400 ms off). Subjects (n = 7) were tested at low to medium contrast levels, which were subjectively equated across chromatic pathways (S, LM, and achromatic). Patterns were presented using LCD goggles.

All subjects showed a small but statistically significant increase in latency in the large negative component (CII) for both L - M and S - (L + M) pathways during inversion. The achromatic pathway also showed a statistically significant increase in latency to the positive component (CI) during inversion.

These results demonstrate that changes in ocular and/or systemic physiology during full-body inversion can result in increased latencies of chromatic and achromatic pattern-onset VEPs.