Value of neural contrast sensitivity on evaluating dark adapted and night vision goggle aided visual performance

Objective To apply neural contrast sensitivity (NCS) on evaluating the dark adapted and night vision goggle (NVG) aided visual performance upon the comparison with contrast sensitivity (CS) and to investigate the value of NCS in the assessment of visual performance. Methods Eight healthy male volunteers (8 eyes) were recruited for this study, and the right eye was tested in this experiment. CS curves of volunteers in light adaptation, dark adaptation and with NVG were measured by Vision Monitor System in different environment luminance levels (10-1-10-4 cd/m2). Modulation transfer function (MTF) curves were measured by optical quality analysis system. NCS was defined as the ratio of CS and MTF. Results In lower and medium frequency range (spatial frequency was 0.6-3.4 cycle/degree), dark adaptation made subject′s NCS and CS mount up considerably in the scotopic vision environment, but less effect in mesopic vision environment. NVG considerably improved subject′s NCS and CS both in scotopic and mesopic vision environments (spatial frequency was 1.1-7.1 cycle/degree) and more effective than in dark adaptation. In high spatial frequency range, neither dark adaptation nor NVG had obvious effect on improving subject′s NCS and CS. Conclusions Both dark adaptation and snooper scopes can improve visual performance in the scotopic vision environment, but snooper scopes is better. CS curves can represent the comprehensive visual performance, NCS reflects the function of the retina-brain neural system. But NCS and MTF would be helpful to find the reasons in case of poor CS measured. The examination combined NCS and MTF with CS is suggested. Key words: Contrast sensitivity; Dark adaptation; Vision; Night vision goggles