Study of visual acuity and reaction time at different contrast levels for military soldiers

Objective To investigate the variation of visual acuity (VA) and reaction time (RT) at different contrast levels with bright and dark background and their relationship for military soldiers with normal VA, and to evaluate the importance of low contrast VA and RT measurement in personnel selection for special branches of the service and conscription physical examination. Methods Fifty-four active-duty army servicemen (108 eyes) with normal VA were enrolled. logMAR VA and RT were measured at four contrast levels (100%, 25%,10%, 5%) with bright and dark background in dark room with multi-functional visual acuity tester (MFVA-100). The measurement values were divided into 8 groups according to the background and contrast level. Results ① VA of lower contrast group was significantly worse than that of higher contrast group (P0.001) with background luminance being identical. With contrast level descending, VA decreased gradually. At the same contrast level, VA of dark background group was significantly worse than that of bright background group (P0.001). ② RT extended gradually with contrast level descending with background luminance being identical. At bright background, there was no significant difference of RT between contrast 10% and 5%(P0.05). However, significant differences were found among the others(P0.05). At dark background, RT of lower contrast group was significantly longer than that of higher contrast group(P0.05). At the same contrast level, RT of dark background was longer than that of bright background, but only at contrast 5% level, there was significant diffe-rence(P0.05). Conclusions The contrast VA of military soldiers with normal VA at bright background was better than at dark background. With luminance weakening and contrast descending, VA decreased individual variation increased, and the RT of stimulant recognition extended gradually. MFVA-100 offers a new sensitive, convenient adjunctive measure of contrast sensitivity which may be useful for identifying the unique visual abilities required for the military.