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Purpose To compare the effect of decentration and tilt on the optical performance of 6 aspheric intraocular lens (IOL) designs in a model eye. Setting Department of Ophthalmology, Graduate School of Medicine, Dokkyo Medical University, Tochigi, Japan. Design Experimental study. Methods In theoretical simulations, the amount of spherical aberration in the IOL was varied to produce residual ocular spherical aberration (range −0.15 to 0.30 μm) at a 6.0 mm entrance pupil. Wavefront aberration analyses were performed with the ZEMAX optical design program (version August 20, 2014) to obtain the ocular root-mean-square values of astigmatism, coma, trefoil, and higher-order aberrations (HOAs) when the IOL was centered on the insertion position and misaligned at a 4.0 mm entrance pupil. The retinal visual images were calculated using the same conditions. Six 20.0 diopter (D) aspheric IOLs and one 20.0 D spherical IOL were used for the experimental studies. Each IOL was inserted in the model eye. The actual alignments were measured using a Scheimpflug camera (EAS-1000). The wavefront aberrations and visual images were gauged using a wavefront analyzer (KR-1W) at several IOL alignments. Results Intraocular lens decentration and tilt increased wavefront aberrations and degraded optical performance. Astigmatism, coma, and HOAs generated by misaligned IOLs were related to the amount of spherical aberration correction of the IOLs. The extent of spherical aberration remained unchanged by the amount of misalignment. Experimental model eye results showed trends similar to theoretical results. Conclusions The spherical aberration correction amount in the aspheric IOL design was critical for the astigmatism, coma, and HOAs generated by the IOL misalignment. Additional spherical aberration corrections led to a more sensitive optical performance degradation resulting from IOL misalignment.

To evaluate the performance of a new formula of intraocular lens (IOL) power calculation (the O formula) based on ray tracing without commonly used parameters, including ultrasound-compatible axial length, keratometry readings, and A-constant.Tokyo Medical Center, Tokyo, Japan.Retrospective consecutive case series.423 eyes (423 patients) implanted with a single-piece, L-loop, acrylic IOL were enrolled. All biometric data for the O formula were obtained by anterior segment swept-source optical coherence tomography (SS-OCT) and SS-OCT-based biometer. The performance of the O formula was compared with those of the Barrett Universal II (BUII) and Kane formulas at 1 month postoperatively. Statistical analysis was applied according to a heteroscedastic test with SD of prediction errors as the main parameter for formula performance.The SD of the O formula (0.426) was statistically significantly lower than that of the BUII formula (0.464, P = .034) but not statistically significantly different from that of the Kane formula (0.433, P = .601). The percentages of patients with refractive prediction errors within ±0.50 diopter (D) and ±1.00 D of the O, BUII, and Kane formulas were 75.4% and 98.6%, 77.1% and 97.9%, and 76.6% and 98.1%, respectively.The O formula, based on ray tracing using SS-OCT-based devices, is one of the promising approaches for IOL power calculation, although additional larger scale studies are needed. It may be used as an alternative in IOL power calculation because of its independence from commonly used parameters.

Correcting spherical and chromatic aberrations in vitro in human eyes provides substantial visual acuity and contrast sensitivity improvements. We found the same improvement in the retinal images using a model eye with/without correction of longitudinal chromatic aberrations (LCAs) and spherical aberrations (SAs). The model eye included an intraocular lens (IOL) and artificial cornea with human ocular LCAs and average human SAs. The optotypes were illuminated using a D65 light source, and the images were obtained using two-dimensional luminance colorimeter. The contrast improvement from the SA correction was higher than the LCA correction, indicating the benefit of an aspheric achromatic IOL.

The numerical solution of ordinary differential equations has been widely used in many fields including wave propagation analysis. To represent a continuous function in terms of its discrete sampled values in a sequence, it should satisfy the sampling theorem. However, in conventional wave propagation analysis, the experiential finite difference technique has generally been used. In this paper, the sampling extension which converges more rapidly than in the case of classical cardinal series is proposed. The extension and aliasing errors including the truncation error are described specifically. The sampling extention is also generalized to include the sampled values of the derivative and integral of the signal.

Recently, harmonic imaging has been widely used for improving image quality in the field of ultrasonic diagnostic. In this research, the evaluation of the quality improvement of the ultrasonic B-mode images by tissue harmonic imaging was attempted by combining this technique with the numerical analysis method. The influence of the inhomogeneous intervening medium on the ultrasonic B-mode images was also considered. Also, the region of interest (ROI) on the B-mode images were compared with the surrounding region to quantify the contrast improvement based on the relative echo level. The image quality improvement of tissue harmonic imaging was also analyzed in consideration of the signal-to-noise ratio (SNR).

The influence of nonuniform transducer velocity distribution in the near-field echo formation scattered from a cavity in steel is analyzed. In the present study, the velocity amplitude on the transducer face was modeled using an offset error function. Using this distribution, the echo waveforms scattered from a cylinder cavity in steel were estimated and compared with the echo estimated using uniform distribution and echo observed experimentally. The estimation accuracy of the near-field echo waveforms were improved quantitatively.

The scattering of wideband ultrasonic pulses from simulated cavities in a metal block was estimated using a mathematical description of the echo based on the expression for echoes reflected from a strongly scattering object. The theoretically estimated echo waveforms and the corresponding Fourier power spectra of the scattered pulses are compared with those obtained experimentally with good agreement. Interpretations show that both the pulse‐time record and the power spectrum can be utilized to detect roughly the shape of a cavity in a metal block.

An analytical description for the radiation field of a planar source by fast converging binomial series expansion is derived. The terms of the series correspond to the Fresnel solution and its derivatives. Consequently, if the Fresnel solution of the diffraction integral is expressed by differential functions, the radiation field can be obtained by calculating the series. As a result of the expansion, this method can be applied to any region except the points on the surface of transducer. The results are compared with the correct computations and those obtained by conventional Fresnel approximation.

Earlier methods in complete symbolic substitution logic used several techniques for coding the binary values. We propose a coding-free method which is designed by using the input and its inverted pattern to recognize both 0 and 1 simultaneously.

An impulse representation for calculating a diffraction wave due to a rigid wedge is described. The method is an approximation of the Biot-Tolstoy rigorous closed-form solution for the diffraction of point source radiation by an infinite rigid wedge. The band-limited time-domain function can be reconstructed to the original waveform if it satisfies the sampling theorem, which assumes that sampling takes place at the lowest permissible sampling rate. Therefore, if the energy is concentrated between the first sampling intervals immediately after the rise time of the time-domain function, the rigorous solution can be approximated as a delta function. This paper shows the description methods of the diffraction field near the ridge in three-dimensional space. Using the proposed impulse representation, numerical simulation was performed and the calculation accuracy was examined.

The quantitative evaluation of ultrasonic displacement in tissue under externally applied forces is a necessary step in the field of ultrasonic diagnostics. In this study, the speckle tracking method is used to investigate the motion artifact produced by a rotating tissue. An analytic prediction of this motion artifact in relation to system characteristics (i.e., beam width, pulse duration, frequency, and phase of the signal) is presented. The tissue is modeled as a random array of numerous point scatterers, and rf signals are computed based on the convolutions between the transmission pulse and the impulse response of each scanning line. These analytical predictions are then compared to the computer simulation of the model. The results show that the artifact resulting from the speckle tracking method depends on the ultrasonic beam parameters. The method is quite general and can be extended to study the effects of other tissue motion, in particular, the deformation of tissue.

Convolution and correlation are closely related operations that are basic to many areas of signal processing. To obtain the frequency component of the signals using discrete Fourier transform (DFT), the continuous signals must first be sampled. A low‐pass antialiasing filter which is simple to implement is proposed. The low‐pass filter has equally good frequency response characteristics and can be used to eliminate possible aliasing effects by ensuring that the signal to be sampled is limited in the spectral content. The impulse response of the sound field was calculated by using the proposed low‐pass antialiasing filter and compared with the rigorous solution to verify the realizability of the filter. The filter was also applied to construct the ultrasonic B‐mode image of a 3‐D phantom model.

The echo formation in the near field of an ultrasonic transducer is strongly influenced by the amplitude distribution of the transducer. In this paper, the velocity amplitude on the face of a plane circular transducer was estimated using on‐axis transient radiation of the actual transducer. The velocity amplitude can be obtained by deconvolving the pressure waveform with the electrical characteristics of the transducer and then integrating the result with respect to time. Using the estimated velocity amplitude, the scattering of wideband ultrasonic pulses from a cylindrical rod was then numerically calculated by applying a mathematical description of the echo [Lawu et al., J. Acoust. Soc. Am. 98, 2809–2818 (1995)]. Results of these estimations agree well with those obtained experimentally. The proposed method improves the accuracy of the echo waveforms scattered by an object in the near field of the transducer.

The velocity amplitude on the transducer face was estimated using the near-field transient radiation on the axis of the circular transducer obtained experimentally. The velocity amplitude can be obtained by deconvolving the pressure waveform with the electrical characteristics of the transducer and then integrating the result. Using the estimated velocity amplitude, the pressure waveforms were numerically calculated and compared with those obtained experimentally.