BackgroundDifferent depthes or distances are prompted with many visual cues on the flat screen.Which kind of depth cues plays a major role in the accommodation of human eyes, in addition, whether this effect exists in the different distance are still below understood.

ObjectiveThis study was to research the effect of the monocular space depth perception on accommodative response at different distances, and to analyze the effect of linear perspective and size-constancy perceptual depth cues on the level and amplitude of accommodative fluctation.

MethodsFour groups of visual targets were designed by FLASH software and placed at the front of eyes with the distance of 50 cm or 33.3 cm, representing static change from far to near and dynamic change from far to near, from near to far respectively.Twenty-six healthy volunteers aged 22-26 years were included in this study, with the spherical power of (-4.06±1.99)D and cylindrical power of (-0.38±0.41)D under the informed consent.The accommodative response and accommodative fluctuations during monocularly watching the targets were recorded at 5 times/second by Grand Seiko WAM 5500 automatic infrared refractor.This study was approved by Ethic Committee of Wenzhou Medical University, and written informed consent was obtained from each subject before entering the study group.

ResultsAt the distance of 50 cm, the accommodative response caused by the depth perception of near was (1.52±0.46)D, the one of distance was (1.37±0.46) D, with a significant difference of 0.15 D under the combined effect of linear perspective and size-constancy ( P=0.016). The accommodative response caused by the depth perception of big car was (1.43±0.35)D, and the one of small car was (1.43±0.36)D, without statistically significant difference under the effect of size-constancy alone ( P=0.467). At the distance of 33.3 cm, the accommodative response caused by the depth perception of near was (2.40±0.53)D, and the one of distance was (2.35±0.51)D, without significant difference under the combined effect of linear perspective and size-constancy ( P=0.379). The accommodative response caused by the depth perception of big car was (2.38±0.48)D, the one of small car was (2.39±0.52)D, without statistically significant difference under the effect of size-constancy alone ( P=0.820). In addition, the total curve of accommodative microfluctuation showed apparent fluctuation periodically caused by the distance perception involving linear perspective only.

ConclusionsMonocular space depth perception has some impacts on the accommodative response at certain distance.Linear perspective, which is one of the depth cues of space perception, plays a major role in the accommodative response.Compared with the size-constancy, linear perspective can provide depth perception at higher level.The size-constancy has a little or contrast impact to the accommodation, because it depends on the assistance from other depth cues like linear perspective.