AIM: To describe the characteristics of modulation transfer function (MTF) of anterior corneal surface, and obtain the the normal reference range of MTF at different spatial frequencies and optical zones of the anteri...AIM: To describe the characteristics of modulation transfer function (MTF) of anterior corneal surface, and obtain the the normal reference range of MTF at different spatial frequencies and optical zones of the anterior corneal surface in myopes. METHODS: Four hundred eyes from 200 patients were examined under SIRIUS corneal topography system. Phoenis analysis software was applied to simulate the MTF curves of anterior corneal surface at vertical and horizontal meridians at the 3, 4, 5, 6, 7mm optical zones of cornea. The MTF values at spatial frequencies of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 and 60 cycles/degree (c/d) were selected. RESULTS: The MTF curve of anterior corneal surface decreased rapidly from low to intermediate frequency (0-15cpd) at various optical zones of cornea, the value decreased to 0 slowly at higher frequency (>15cpd). With the increase of the optical zones of cornea, MTF curve decreased gradually. 3) In the range of 3 mm- 6 mm optical zones of the cornea, the MTF values measured at horizontal meridian were greater than the corresponding values at horizontal meridian of each spatial frequency, the difference was statistically significant (P<0.05). At 7 mm optical zones of cornea, the MTF values measured at horizontal meridian were less than the corresponding values at vertical meridian at 10-60 spatial frequencies (cpd), and the difference was statistically significant in 25, 30, 35, 40, 45, 50 cpd(P<0.05). CONCLUSION: MTF can be used to describe the imaging quality of optical systems at anterior corneal surface objectively in detail.展开更多
This paper investigates the applicabilitles of pole-zero model and wave propagation theory in estimating the phase characteristics of vibrating systems. The measured phase spectra are compared with the estlmated rever...This paper investigates the applicabilitles of pole-zero model and wave propagation theory in estimating the phase characteristics of vibrating systems. The measured phase spectra are compared with the estlmated reverberant phase limit and wave propagation phase. The relations between transfer function phase and frequency, damping, and separation distance are described. The present results show that the pole-zero model provides a reasonable estimation of the reverberant phase limit in low frequency band below an identified transition frequency.The reverberant phase is linearly dependent on frequency in this band, but from the transition frequency and onwards the phase increases only with the square root of frequency. This behavior is characteristic for free propagating waves展开更多
文摘AIM: To describe the characteristics of modulation transfer function (MTF) of anterior corneal surface, and obtain the the normal reference range of MTF at different spatial frequencies and optical zones of the anterior corneal surface in myopes. METHODS: Four hundred eyes from 200 patients were examined under SIRIUS corneal topography system. Phoenis analysis software was applied to simulate the MTF curves of anterior corneal surface at vertical and horizontal meridians at the 3, 4, 5, 6, 7mm optical zones of cornea. The MTF values at spatial frequencies of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55 and 60 cycles/degree (c/d) were selected. RESULTS: The MTF curve of anterior corneal surface decreased rapidly from low to intermediate frequency (0-15cpd) at various optical zones of cornea, the value decreased to 0 slowly at higher frequency (>15cpd). With the increase of the optical zones of cornea, MTF curve decreased gradually. 3) In the range of 3 mm- 6 mm optical zones of the cornea, the MTF values measured at horizontal meridian were greater than the corresponding values at horizontal meridian of each spatial frequency, the difference was statistically significant (P<0.05). At 7 mm optical zones of cornea, the MTF values measured at horizontal meridian were less than the corresponding values at vertical meridian at 10-60 spatial frequencies (cpd), and the difference was statistically significant in 25, 30, 35, 40, 45, 50 cpd(P<0.05). CONCLUSION: MTF can be used to describe the imaging quality of optical systems at anterior corneal surface objectively in detail.
文摘This paper investigates the applicabilitles of pole-zero model and wave propagation theory in estimating the phase characteristics of vibrating systems. The measured phase spectra are compared with the estlmated reverberant phase limit and wave propagation phase. The relations between transfer function phase and frequency, damping, and separation distance are described. The present results show that the pole-zero model provides a reasonable estimation of the reverberant phase limit in low frequency band below an identified transition frequency.The reverberant phase is linearly dependent on frequency in this band, but from the transition frequency and onwards the phase increases only with the square root of frequency. This behavior is characteristic for free propagating waves
基金Natural Science Foundation of Zhejiang Province(Y1110125)Program for Innovative Research Team,Zhejiang Normal University,Jinhua,Zhejiang Province,P.R.China
