Purpose: Contrast sensitivity (CS) is important for our everyday and working vision, and it is affected by lumination. Pilots are dependent on a precise and strong visual acuity. Helicopter pilots are exposed to the combination of height and vibration, and operate under different light settings. The effect of mild hypoxia and vibration in combination on CS under different levels of light is not known. This study aims to explore this relationship.
Methods: CS was measured on 16 healthy subjects with a visual acuity of minimum 1.0 (20/20), under five different light settings (0.02, 0.12, 0.22, 1.5 and 54.0 lux). Each test person underwent four CS-tests, where they were randomized to four different combinations of height (10 000 feet) and vibration. The experiments were performed in a hypobaric altitude chamber with a vibration platform providing whole body vibration in the z-axis with a frequency of 17Hz with amplitude 1ms-2. The sum of the score value from the 5 different frequencies of the CS test was calculated, and a general linear model (GLM) procedure was carried out to identify the effect of the different factors. All test persons were included in the study.
Results: Mean SpO2 at 10 000 feet was 91%. The effect of the different light settings in incremental order with scotopic (0.02 lux) as reference was 153.7 for 0.12 lux, 177.8 for 0.22 lux and 336.2 for photopic conditions (54 lux), p<0.001. Vibration gave a significant negative effect of -22.8, p=0.031 and hypoxia at this level was not found important (p=0.14).
Conclusion: Vibrations equal to a typical helicopter negatively affects contrast sensitivity to a certain extent and in magnitude corresponds to the difference in illumination levels from 0.22 to 0.12 lux.