Purpose: To design and test an optical system to measure the optical quality of post mortem lenses during simulated accommodation. Methods: An optical bench top system was designed to measure the point spread function and calculate the modulation transfer function (MTF) of monkey and human ex-vivo crystalline lenses. The system consists of a super luminescent diode emitting at 850nm, collimated into a 3mm beam which is focused by the ex-vivo lens under test. The intensity distribution at the focus (point spread function) is re-imaged and magnified onto a beam profiler CCD camera. The optical quality in terms of spatial frequency response (modulation transfer function) is calculated by Fourier transform of the point spread function. The system was used on ex-vivo lenses with attached zonules, ciliary body and sclera. The sclera was glued to 8 separate PMMA segments and stretched radial by 5mm on an accommodation simulating lens stretching device. The point spread function was measured for each lens in the relaxed and stretched state for 5 human (ages 38-86 years) and 5 cynomolgus monkey (ages 53 - 67 months) fresh post mortem crystalline lenses. Results: Stretching induced measurable changes in the MTF. The cutoff frequency increased from 54.4±13.6 lp/mm unstretched to 59.5±21.4 lp/mm stretched in the post-presbyopic human and from 51.9±24.7 lp/mm unstretched to 57.7±18.5 lp/mm stretched cynomolgus monkey lenses. Conclusion: The results demonstrate the feasibility of measuring the optical quality of ex-vivo human and cynomolgus monkey lenses during simulated accommodation. Additional experiments are underway to quantify changes in optical quality induced by stretching.
To simulate the retinal images of the human eye including asymmetric aberrations is very important and interesting with using a new point spread function analysis system (PSFAS). The point light source (SLD 840 nm) was projected onto the subject's eye and the reflected image at the retina was captured by the charge coupled device which was in the conjugated point with the retina (double-pass formula). To obtain the modulation transfer function (MTF) of the optical system, equal sized apertures were used as entrance and exit pupils. To obtain the phase transfer function (PTF), unequal sized apertures were used. To obtain the simulated retinal images, the Fourier spectrum of the original chart was multiplied by the MTF and the PTF as the phase term of the original chart was added. The inverse Fourier transformation of the Fourier spectrum term and the phase term was the simulated retinal image. The simulated retinal images of the Landolt rings in human eyes might sufficiently involve asymmetric aberrations without losing the high-frequency range of spatial frequency. The PSFAS can simulate retinal images, which are based on not only the information from the symmetric aberrations and the scattering and absorption of haze but also on the information from the asymmetric aberrations. The PSFAS can objectively evaluate the characteristics of the human optical system and therefore is useful in an ophthalmology clinic setting.
We developed a new point spread function (PSF) analysis system (PSFAS) to study the optical system of the human eye. An infrared point light source is projected on the retina, then the single-pass modulation transfer function (MTF) is derived from teh iamge of incoherent polarized reflection double-pass PSF measured by PSFAS. The retinal images and the contrast characteristics of various sized Landolt's rings then are simulated with the single-pass PSF calculated by the single-pass MTF. The visual acuity (VA) is predicted from the retinal images. The single-pass MTF and the contrast characteristics of aged subjects were clearly lower than those of a young subject in mid-frequency, though the cut-off frequency was similar in the two subjects. The predicted VA from the simulated retinal images agreed with the actual VA in normal subjects and in those with myopic astigmatism. This becomes a useful system for elucidating the optical characteristics of the human eye. In addition, the visual simulation obtained using this system is clinically useful for objectively evaluating visual function.
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