Distributional characteristics of different contrast visual acuity under bright background in military helicopter flight cadets

Objective To investigate the variation of visual acuity(VA) at different contrast levels under bright background in military helicopter flight cadets. Methods Eighty-six military helicopter flight cadets(172 eyes) with normal VA were enrolled. log MAR VA was measured at 4 contrast levels(100%, 25%, 10%, 5%) under bright background with multi-functional visual acuity tester(MFVA-100). The relationship of VA at different contrast levels under bright background was analyzed. Results log MAR VA of 100%, 25%, 10%, and 5% in right eye were-0.001±0.128, 0.257±0.152, 0.537±0.158, 0.726±0.174, respectively; log MAR VA of 100%, 25%, 10%, and 5% in left eye were 0.003±0.127, 0.248±0.156, 0.521±0.170, 0.706±0.197, respectively. Visual acuity decreased gradually with a decrease in the contrast level, and it was significantly better at high contrast than that at low contrast(P 0.05). Visual acuity(VA) was of no statistically significant difference between right and left eye in the same contrast level(P 0.05). Visual acuity at 100% contrast was linearly related to the visual acuity at 25%, 10%, 5% contrasts respectively(P 0.05). Conclusion The different contrast levels significantly affect contrast visual acuity. The lower the contrast is, the larger visual acuity changes.