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System identification problems often arise where the only modeling records available consist of multiple short-time-duration signals. This motivates the development of a modeling approach that is tailored for this situation. An identification algorithm is presented here for parameter estimation based on minimizing the simulated prediction error, across multiple signals. The additional complexity of estimating the initial states corresponding to each signal is removed from the estimation algorithm. A numerical simulation demonstrates that the proposed algorithm performs well in comparison to the often-used least squares method (which leads to biased estimates when identifying systems from measurement noise corrupted signals). The approach is applied to the identification of the passive oculomotor plant; parameters are estimated that describe the dynamics of the plant, which represent the time constants of the visco-elastic elements that characterize the plant connective tissue. Index Terms--Initial conditions, oculomotor plant, output error, parameter estimation, state-space.

We developed a new exposure system to irradiate microwaves locally on a rabbit eye using a small coaxial-to-waveguide adapter filled with low-loss dielectric material as an antenna. A numerical rabbit model was also developed using X-ray computer tomography images, and the specific absorption rates (SARs) in the rabbit, especially in the eye, were analyzed with the finite-difference time-domain method. The temperature elevation in the exposed eye was also evaluated by solving a bioheat equation. Our exposure system can generate incident power density of 15 mW/[cm.sup.2] at the surface of a rabbit eye with input power of 1 W. When the incident power density on the rabbit eye is 300 mW/[cm.sup.2], average SAR over the exposed eye and the whole body were approximately 108 and 1.8 W/kg, respectively. The exposure system can realize localized exposure to the eye with the ratio of exposed-eye averaged SAR to the whole-body averaged SAR was 60. The developed exposure system can achieve high-intensity exposure such as the threshold of cataracts, i.e., the eye-averaged SAR over 100 W/kg or the lens temperature over 41 [degrees]C with the incident power density of 300mW/[cm.sup.2] without significant whole-body thermal stresses. Index Terms--Cataract, eye, microwave, ocular effect, specific absorption rate (SAR), temperature.

In this paper, we study the human oculomotor system as a simple mechanical control system. It is a well known physiological fact that all eye movements obey Listing's law, which states that eye orientations form a subset consisting of rotation matrices for which the axes are orthogonal to the normal gaze direction. First, we discuss the geometry of this restricted configuration space (referred to as the Listing space). Then we formulate the system as a simple mechanical control system with a holonomic constraint. We propose a realistic model with musculotendon complexes and address the question of controlling the gaze. As an example, an optimal energy control problem is formulated and numerically solved. Index Terms--Eye movements, geodesics, Hill model, Listing's law, simple mechanical control systems.

Studies on the behavior of the vestibulo-ocular reflex (VOR) reveal that the monocular reflex gain is adjusted according to target position relative to each eye. In this paper, we present a nonlinear approach in modeling the viewing-context dependency of the slow-phase angular VOR. We show that including appropriate nonlinearities in the responses of premotor neurons in the brainstem is sufficient to account for the online modulation of the VOR with target position. This approach allows very complex behaviors in response to sensory patterns without resorting to currently assumed cortical computations. A local premotor topology with nonlinear properties has repercussions in the study of all ocular reflexes, since it implies context dependent dynamics in all behavioral responses (pursuit, optokinetic, VOR, saccades, etc.) that share this network. Local nonlinearities in spinal circuits could similarly influence the context dependence of other motor systems (such as stretch reflex modulation during rhythmic walking). Index Terms--Eye movement, neural topology, reflex modulation, sensory-motor mapping, vestibulo-ocular reflex.

In refractive surgery, especially wavefront-guided refractive surgery, correct registration of the treatment to the cornea is of paramount importance. The specificity of the custom ablation formula requires that the ablation be applied to the cornea only when it has been precisely aligned with the mapped area. If, however, the eye has rotated between measurement and ablation, and this cyclotorsion is not compensated for, the rotational misalignment could impair the effectiveness of the refractive surgery. To achieve precise registration, a noninvasive method for torsional rotational alignment of the captured wavefront image to the patient's eyes at surgery has been developed. This method applies a common coordinate system to the wavefront and the eye. Video cameras on the laser and wavefront devices precisely establish the spatial relationship between the optics of the eye and the natural features of the iris, enabling the surgeon to identify and compensate for cyclotorsional eye motion, whatever its cause. Index Terms--Biomedical image processing, image orientation analysis, image registration, motion compensation.

This paper investigates the effect of frequency, polarization, and angle of incidence of an electromagnetic (EM) wave on the specific absorption rate (SAR) and maximum temperature increase in the human eye at 900 MHz, 1.5 GHz, and 1.9 GHz. In particular, the temperature increase in the eye is compared for near-field and far-field exposures. The difference of a maximum temperature increase in the lens is also discussed between the head models of an adult and children. Throughout the investigations, our attention is paid to a maximum temperature increase in the lens for SAR values prescribed in safety standards. For the results of our investigation, the SAR and temperature increase in the eye are found to be largely dependent on the separation between the eye and a source, and the frequency, polarization, and angle of incidence of the EM wave. The maximum temperature increase (0.303 [degrees]C-0.349 [degrees]C) in the lens of the adult for the SAR value of 2.0 W/kg for the eye tissue (about 10 g) is marginally affected by the above-mentioned factors. No clear difference of a maximum temperature increase in the lens at the SAR limit is observed between the adult and children models. Index Terms--Biological effects of electromagnetic radiation, dosimetry, finite-difference time-domain (FDTD) methods.

The optics of the human eye are not static in steady viewing conditions and exhibit microfluctuations. Previous methods used for analyzing dynamic changes in the eye's optics include simple Fourier-transform-based methods, which have been used in studies of the eye's accommodation response. However, dedicated tools for the analysis of dynamic wavefront aberrations have not been reported. We propose a set of signal processing tools, the combination of which uncovers aspects of the dynamics of eye's optical aberrations which were hidden from conventional analysis techniques. The methodology includes extraction of artifacts from potentially significant eye movements, filtering, optimal parametric signal modeling, and frequency and time-frequency representations. The exposition of the techniques and their advantages over traditional techniques is illustrated for real dynamic eye wavefront aberration measurements. Index Terms--Aberrations, biomedical signal processing, eye, wavefront sensing.

An explicit finite-difference time-domain formulation of the bio-heat equation is employed with a three-dimensional head eye model to evaluate the temperature increase in the eye and surrounding head tissues due to the operation of the implanted stimulator IC chip of a retinal prosthesis designed to restore partial vision to the blind. As a first step, a validation of the thermal model and method used is carried out by comparison with in vivo measurements of intraocular heating performed in the eyes of dogs. Induced temperature increase in the eye and surrounding tissues is then estimated for several different operational conditions of the implanted chip. In the vitreous cavity, temperature elevation of 0.26[degrees]C is observed after 26 min for a chip dissipating 12.4 mW when positioned in the mid-vitreous cavity while it is 0.16[degrees]C when the chip is positioned in the anterior portion between the eye's ciliary muscles. Corresponding temperature rises observed on chip are 0.82[degrees]C for both the positions of the chip. A comprehensive account of temperature elevations in different tissues under different operational conditions is presented. Index Terms--Bio-heat equation, dosimetry, retinal prosthesis, thermal elevation.

This is the second of a series of two papers on the thermal increase in the human eye and head in response to an implanted retinal stimulator. This paper provides specific absorption rates induced in the human head by the extraocular unit and the temperature increases associated with induced electromagnetic fields and power dissipation of the implanted microchip. Results are provided for different assumptions about choroid blood flow. It is shown that computed results associated with the power dissipation of the implanted microchip, corresponding to temperature increases of approximately 0.6[degrees]C in the midvitreous of the eye and 0.2[degrees]C in the retina, closely parallel in-vivo experimental results in animals. Index Terms--Age-related macular degeneration, finite-difference time domain (FDTD), retina prosthesis, retinitis pigmentosa, specific absorption rate (SAR), stimulator IC, temperature, thermal simulation.

The soft-tissue thermal index does not adequately track temperature rise within the eye during insonation. Research with frequencies between 7.0 and 40 MHZ show only insignificant results.

This study proposed an improved heat transfer model of the eye for exposure to electromagnetic (EM) waves. Particular attention was paid to the difference from the simplified heat transfer model commonly used in this field. From our computational results, the temperature elevation in the eye calculated with the simplified heat transfer model was largely influenced by the EM absorption outside the eyeball, but not when we used our improved model. Index Terms--Electromagnetic exposures, eye safety, heat transfer model, temperature elevation.