City Research Online

Abstract

This research project has considered how advanced vision tests can be used to optimise aircrew performance both as a means for characterising visual function of aircrew and as a method of better understanding mesopic visual function. The first study defined a test protocol for the Rod Cone Sensitivity (RCS) test with the aim of characterising the sensitivity of rod and cone mediated vision to mean modulated flickering stimuli presented at the fovea and peripherally at 5⁰ eccentricity. The luminance, chromaticity, and temporal modulation of the two stimulus conditions were configured to promote either a rod or cone mediated response after a short adaptation time of two minutes. Subsequently, the test was utilised to characterise binocular summation both at the fovea and at 5⁰ eccentricity with results confirming cone mediated vision based up probability summation at the fovea. The study also identified that binocular summation of stimuli presented peripherally resulted from a combination of probability and neural summation processes for both test stimulus conditions of the RCS test. The second study confirmed that the chromaticity of the rod condition instigated a rod mediated response based upon the scotopic dependency of the pre-stimulus diameter of the pupil light reflex. Using the two stimulus conditions to characterise the transient pupil light reflex to a 100% contrast stimulus for luminance values from -3 to 2 log cdm-2 enabled models for the constriction amplitude and latency as a function of retinal illuminance to be developed. The results have assisted in determining the transition point between rod and cone mediated visual function as a function of scotopic retinal illuminance and how this point might be affected by changes caused by aging to the optics of the eye and retina. The last study applied the RCS test enabling the comparison of visual function under conditions of: normobaric normoxia; hypobaric hypoxia equivalent to 3048m altitude; and normobaric hyperoxia (100%). The participants demonstrated a statistically significant loss of sensitivity at 5⁰ eccentricity at 0.5cd.m-2 and 24cd.m-2 due to hypobaric hypoxia, when compared to the normobaric hyperoxia condition. In addition, the study demonstrated that an inspired fraction of 43% oxygen was able to mitigate against the effects of hypobaric hypoxia at 3048m altitude. Together the studies have highlighted the differences in sensitivity and function of the retina at the fovea and at 5⁰ eccentricity at mesopic light levels, and how the peripheral retina is more sensitive to changes in choroidal oxygen tension.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RE Ophthalmology T Technology > TL Motor vehicles. Aeronautics. Astronautics
Departments:	School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses School of Health & Psychological Sciences > Optometry & Visual Sciences

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