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


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Highsmith
Jennifer
J
Department of Psychology, University of Nevada, Reno, 89557, USA. highsmit@unr.nevada.edu
Crognale
Michael A
MA
D000328:Adult; D003116:Color; D005074:Evoked Potentials, Visual; D005260:Female; D018475:Head-Down Tilt / Q000502:physiology*; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D010775:Photic Stimulation / Q000379:methods*; D011930:Reaction Time; D014795:Visual Pathways / Q000502:physiology; D055815:Young Adult