Abstract
Abstract: :
Purpose: To establish how the pattern of optical aberrations of the eye changes when the human body is subjected to large G–forces. The long–term aim of the project is to establish which of the current refractive surgery techniques yields best overall performance in the fighter aircraft environment. Methods: Preliminary measurements were carried out to assess any changes in the performance of the equipment under large G–forces. A Tscherning Principle aberrometer (Allegretto Wave Analyzer, Wavelight, Germany) fitted with an eye–tracking device was used to measure the wavefront aberration of the eye when the pilot’s body is subjected to G–forces acting in the head to toe direction (+Gz). The instrument was installed in a human centrifuge capable of +12Gz acceleration. The performance of the aberrometer under +4Gz was assessed experimentally using an artificial eye. The subjects used in this study were air force pilots in training with centrifuge experience who had passed the medical examination. The wavefront aberration of the eye was quantified using Zernike Polynomials. Results:300 measurements on the model eye showed no statistically significant changes in wavefront aberrations under +4 Gz forces. The data confirmed the proper functioning of the equipment. A cross–sectional study of 20 subjects was then performed taking measurements of the right eye of each subject under an acceleration of up to +3 Gz. Measurements in the 20 human eyes revealed a significant increase in defocus (C20, p=0.022), coma (C31, p=0.018), higher–order coma (C5–1, p=0.022) and spherical aberration (C60, p=0.002), as a result of +1 Gz to +3 Gz increase in acceleration. The change in defocus is equivalent 0.10 dioptres, a value that may not be functionally significant. Conclusions:The findings of this study reveal significant changes in the aberration pattern of the eye under +3 Gz acceleration. Further studies are needed to establish whether the small but significant changes in defocus and other wavefront aberration coefficients reflect transient changes in accommodation or changes in the structural properties of the eye when subjected to +3Gz forces. One also needs to establish how ametropic eyes behave under these experimental conditions before this investigation can be extended to compare different corneal refractive surgery techniques. In addition, one needs to investigate the extent to which the small increase in wavefront aberrations of the eye has any significant effect on the pilot’s functional visual performance. Acknowledgements: I acknowledge the support received from the German Air Force for providing the use of the centrifuge. I am also grateful to the pilots who acted as subjects in this study.
Keywords: optical properties • refractive surgery: optical quality • visual acuity