Biomedical subjects
Publications and source records attributed to D H Brennan.
The control of high-speed aircraft is a demanding task in which rapid decisions, based on visually acquired information, must frequently be made. Glare, both direct and veiling, is a prime cause of visual degradation in flight. The visual effects of glare are discussed together with means of reducing its consequences. In addition, the visual sequelae of looking at a nuclear fireball are discussed together with means of providing protection.
The time to detect each of three underwater lights by six subjects was measured in clear and turbid (attenuation coefficient = 4.2.m-1) water, at distances of 1.54 m and 3.1 m, from two viewing angles, straight ahead (0 degrees) or 65 degrees to one side, and under three levels of ambient illumination. The lights were viewed either through a window, to simulate the use of a face mask, or with the subjects immersed. All lights were detected rapidly (less than 1 s) when viewed through the window in clear water. In turbid conditions, none of the lights was seen at 3.1 m by any subject. At a 1.54 m viewing distance, reliable detection by immersed subjects was found only in the clear water under the two darker ambient illuminations. In turbid water, detection was unreliable. We conclude that the design of underwater escape lighting should not rely on visibility over distances greater than 1.5 m, and that an illuminated guide-bar might provide valuable assistance in directing escape from aircraft.
The effect of a reversible cholinesterase inhibitor (pyridostigmine: 30 mg, 8-hourly for 3 days) on psychomotor performance and visual function and on the electrical activity of the brain was studied in healthy man. It was not possible to detect any change during the six individual experimental sessions over the 3 days, but with pooling of the data there was a drug effect. The threshold for detection of a flickering light was increased and less responses were missed on a dynamic visual-acuity task. Visuo-motor coordination was impaired. The observations were consistent with the known activity of the drug and suggest an increase in central arousal and minimal alteration in motor coordination.
Seventeen officer aircrew, wearing soft contact lenses, were subjected to adverse conditions likely to be encountered in military aviation. The stresses included hypoxia, rapid decompression, pressure breathing, vibration, climatic extremes, G forces, and the prolonged wearing of an aircrew respirator. Their visual performance wearing contact lenses under stress did not differ significantly from the control values; either when wearing corrective flying spectacles or contact lenses when not under stress. It is considered that from the environmental standpoint soft contact lenses are suitable for aircrew. As contact lenses may not be tolerated by all, and may cause undesirable side-effects in some, their use should be restricted to the aircrew to whom they offer the maximum advantages. The group most likely to benefit are young, well motivated myopes flying fast jets.
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