The point spread function system and its value in optical image quality assessment

Objective To investigate the imaging characteristics of human eyes with the point spread function analysis system (PSF). Methods A PSF 1000 analyzer was used to measure the retinal image quality of the myopic eyes of 22 subjects. The modulation transfer function (MTF) curve was recorded and evaluated for pupil sizes of 3 mm and 6 mm. Twelve points on the MTF curve of the PSF, which were equivalent to the 12 points of a LogMar VA chart (4.0~5.1), were chosen for analysis. Results ①PSF reflects the deviation of light intensity distribution and position. The PSF analysis system could describe the imaging characteristics of the eyes with an MTF curve. The curve obviously declined from the low frequency to the middle frequency section, and was reduced to zero in the high frequency section, which objectively showed the change in imaging characteristics of the eyes from the low to high frequency areas. ②The MTF curve of each eye was enantiomorphous symmetrical. ③Individual MTF values were quite different (e.g., when the spatial frequency was 3.00 c/d, MTF values were from 0.68 to 0.98 for a 3 mm pupil size and from 0.51 to 0.85 for a 6 mm pupil size). ④MTF values measured with a simulated 3 mm pupil size were significantly different from those measured with a simulated 6 mm pupil. Conclusion PSF analysis expressed different kinds of optical imaging characteristics in human eyes. It integrated the impact of aberration, diffraction and dispersion, objectively evaluating the retinal imaging quality of the optic system.