Research On Ground Simulation Experience Method And Disposal Measures Of Pilots’ Night Myopia

The flight accident rate in night training is higher than that of day training.How to maintain safety during night flight is an important issue in the aviation field.According to the requirements of"night combat and night training"by the Central Military Commission（CMC）.Night flight training,especially the night training close to the actual battlefield,has come up with new requirements on training equipment,training methods,flight performance and flight safety.In 2018,the air force issued"the Aviation Physiological Training Program"first time,which included night vision physiological training contents.However,it was not comprehensive and systematic enough and lacked corresponding training means.When flying in the night,the pilot would face reduced visibility or unfamiliar airport environment,there would occur series visual physiological and psychological phenomena,such as blind spot,the color of the Purkinje displacement,night myopia,black holes illusion,which might endanger flight safety.Thus,enhancing the visual physiology of pilots’visual physiology knowledge,and carrying out night training are particularly important.Night myopia is a physiological phenomenon.When the ambient brightness is less than a certain level,there would be lack of the effective visual stimulation in the visual field,and the distant point will move closer and the distant target would be unclear.Therefore,the phenomenon of night myopia will threaten flight safety,especially during relative flight and approaching landing,which may result in reduced effective visual distance,reduced visual response time and developing illusion of"from near to far by mistake"and"from low to high by mistake".There is a lack of training measures for pilots to experience and overcome night myopia.This study aims to establish a ground simulation experience method for night myopia and increase pilots’awareness and real feelings of night myopia.At the same time,based on the simulation experience of night myopia,the influence factors of night myopia and the common night myopia disposal measures were explored.Objects and methods1.To establish the night myopia ground simulation experience method based on the mechanism of night myopia in a dark environment.Because of lacking visible of reference view（under condition of empty field）,the eye ciliary muscle is in a state of involuntary regulation,making eyes in the myopia status and not seeing the distant target.According to this mechanism,we tried to change the laboratory low-light environment,object size,object distance,object brightness and other parameters.Finally,we established the following experience method.The subjects were in dark environment for 20 minutes after dark adaptation and observed the weak light target 6 m far location（the subjects were unable to find the target and the target light intensity was determined by preliminary forecast experiments）and moved slowly in the direction of the target（speed was 10²0 cm/s）.When subjects found the weak light marked point A and diopter was measured by infrared refractive screening instrument.After that,the subject stared at the low-light visual target and slowly moved backward when the subjects reported the disappearance of the target.Then point B was recorded and the diopter of point B was measured at the same time.We made punctiform weak light and"E"-shaped weak light with controllable luminance.Measuring the distance L_A between point A and the visual target and the distance L_ABB between point B and point A through the infrared rangefinder.Eye movement trajectory and pupil changes in real time were detected by eye tracker monitors,which provided the subjects with visual physiological objective indicators.Twenty healthy subjects were selected to verify the established method of simulating night myopia experience,and the relationship between distance indexes L_A and L_AB and refractive changes of night myopia directly measured were established.2.20 healthy subjects（Diopter:-0.5 D⁺0.5 D）were selected to observe the changes of L_A and L_AB under the conditions of different brightness and size of visual standards by using the established experience method of ground simulation of night myopia.Meanwhile,10 emmetropes（Diopter:-0.5 D⁺0.5 D）and 10 subjects with mild myopia（Diopter:-4D^-1 D）were selected to observe the effects of myopia on L_A and L_AB.3.20 healthy subjects（Diopter:-0.5 D⁺0.5 D）were selected to observe the effects of factors such as different blinking speeds（once/three seconds and once/five seconds）,different scanning frequencies（one cycle/five seconds and one cycle/ten seconds）,single and double eyes focus（double eye,dominant single eye and non-dominant single eye）and myopia correction glasses（+0.5 D and+1 D）on night myopia L_A and L_AB.Results1.The successful rate of the simulation experience method for night myopia was 100%.Combined with the laboratory conditions,it was found that the order of magnitude of the optimal visual standard brightness was 10^-3 cd/m².When the brightness of the punctiform scale was 1×10^-3 cd/m²,the regression equation of L_A and（diopter _B-diopter _A）was:（diopter _B-diopter _A）=0.21 L_A-0.727（R²=0.736）and the regression equation of L_AB and（diopter _B-diopter _A）was:（diopter _B-diopter _A）=-0.48 L_AB-0.101（R²=0.781）.2.When the brightness of the punctiform weak light visual standard was on the order of 10^-3 cd/m²,the more the brightness increased,the smaller the L_AB was（P<0.05）,and the larger the L_A was（P<0.05）.However,when brightness of the"E"-shaped weak light level was in the order of 1.1×10^-33 cd/m² and 1.1×10^-44 cd/m²,the greater the brightness was,the greater the L_A was（P<0.05）,while the L_AB existed no significant difference（P>0.05）.When the brightness of the"E"shape visual standard was 1.1×10^-33 cd/m²,L_A increased（P<0.05）and L_AB decreased（P<0.05）with the increase of the visual standard size.When the subject was the mildly myopic,L_A decreased（P<0.05）and L_AB increased（P<0.05）compared with the emmetropias.3.The blink rate of once per 5 s（blinking every five seconds）,the scanning movement of once per 10 s（scanning every 10 seconds）and the myopia correction lens of 1 D could significantly reduce L_AB（P<0.05）and increase L_A（P<0.05）.Meanwhile,compared with monocular fixation of non-dominant eyes,binocular fixation could also significantly reduce L_AB and increase L_A（P<0.05）.Conclusions1.We successfully established a standardized method for ground simulation of nocturnal myopia,which could change the abstract and imperceptible diopter into the distance changes.The flight personnel could truly experience the phenomenon of night myopia,so as to better apply to the physiological training of pilots’night vision.2.Night myopia is closely related to the brightness and size of the visual standard and the myopia degree of the subjects themselves,thus providing a theoretical basis for us to evaluate and predict night myopia.3.Night myopia could be reduced to some extent by blinking,eye scanning and wearing myopia correction glasses.At the same time binocular gaze could also reduce the level of night myopia.In practice,we could choose suitable methods to dispose night myopia.4.We believe that the occurrence of black hole illusion is closely related to the phenomenon of night myopia.The experience method established in this study could be applied to the simulation training of black hole illusion experience and overcoming for flight personnel,which has important aviation medical significance.