Speculum-free portable preterm imaging system.

Significance: Preterm birth is defined as a birth before 37 weeks of gestation and is one of the leading contributors to infant mortality rates globally. Premature birth can lead to life-long developmental impairment for the child. Unfortunately, there is a significant lack of tools to diagnose preterm birth risk, which limits patient care and the development of new therapies. Aim: To develop a speculum-free, portable preterm imaging system (PPRIM) for cervical imaging; testing of the PPRIM system to resolve polarization properties of birefringent samples; and testing of the PPRIM under an IRB on healthy, non-pregnant volunteers for visualization and polarization analysis of cervical images. Approach: The PPRIM can perform 4×3 Mueller-matrix imaging to characterize the remodeling of the uterine cervix during pregnancy. The PPRIM is built with a polarized imaging probe and a flexible insertable sheath made with a compatible flexible rubber-like material to maximize comfort and ease of use. Results: The PPRIM device is developed to meet specific design specifications as a speculum-free, portable, and comfortable imaging system with polarized imaging capabilities. This system comprises a main imaging component and a flexible silicone inserter. The inserter is designed to maximize comfort and usability for the patient. The PPRIM shows high-resolution imaging capabilities at the 20 mm working distance and 25 mm circular field of view. The PPRIM demonstrates the ability to resolve birefringent sample orientation and full field capture of a healthy, non-pregnant cervix. Conclusion: The development of the PPRIM aims to improve access to the standard of care for women's reproductive health using polarized Mueller-matrix imaging of the cervix and reduce infant and maternal mortality rates and better quality of life.

Snapshot imaging Mueller matrix polarimeter using modified Savart polariscopes.

We present a snapshot imaging Mueller matrix polarimeter using modified Savart polariscopes (MSP-SIMMP). The MSP-SIMMP contains both the polarizing optics and the analyzing optics encoding all Mueller matrix components of the sample into the interferogram by the spatial modulation technique. An interference model and the methods of reconstruction and calibration are discussed. To demonstrate the feasibility of the proposed MSP-SIMMP, the numerical simulation and the laboratory experiment of a design example are presented. The remarkable advantage of the MSP-SIMMP is easy to calibrate. Moreover, compared with conventional imaging Mueller matrix polarimeters with rotating parts, the advantage of the proposed instrument is simple, compact, snapshot-enabled, and stationary (no moving parts).

Anamorphic zoom lens based on rotating cylindrical lenses.

An anamorphic zoom lens is designed for altering the size and aspect ratio of a laser beam. The design is based on using a Galilean beam expander in which the optical elements consist of two rotating cylinders. The rotation of the cylinders allows the spherical and cylindrical powers of the rotating cylindrical lens to be altered in such a manner that the magnification is anamorphic. A simple anamorphic zoom lens based on rotating cylindrical lenses is designed and then implemented. Operation of the anamorphic lens demonstrates a 1 to 1 to 10 to 1 aspect ratio beam conversion.

Design and implementation of a portable colposcope Mueller matrix polarimeter.

SIGNIFICANCE: Mueller matrix polarimetry can provide useful information about the function and structure of the extracellular matrix. A portable and low-cost system could facilitate the clinical assessment of cervical anomalies in low-resource settings. AIM: We introduce a low-cost snapshot Mueller matrix polarimeter that does not require external power, has no moving parts, and can acquire a full Mueller matrix in ∼1 s, to conduct a feasibility study for cervical imaging in the low-resource setting. APPROACH: A snapshot system based on two sets of Savart plates, a ring illuminator with polarizing elements (generating four polarization states), and one camera is introduced. Stokes vectors are formulated to recover the polarization properties of the sample. Then, using Mueller matrix decomposition, the depolarization and retardance information is extracted. RESULTS: We report the results on 16 healthy individuals (out of 22 patients imaged), whose Pap smear showed no malignant findings from mobile clinics in rural region of Mysore, India. The depolarization and retardance information was in agreement with previous reports. CONCLUSIONS: We introduce an imaging system and conducted a feasibility study on healthy individuals. This work could futurely translate into diagnostic applications to provide a quantitative platform in the clinical environment (e.g., cervical cancer screening).

Relating wavefront error to visual acuity in pre- and post-LASIK eyes: a comparison of methods.

Contrast threshold and visual Strehl ratio methods are used to predict visual acuity from wavefront error for a sample population of pre- and post-LASIK patients. Relative error (in logMAR) between predicted and measured visual acuity values are computed for each method and compared using paired t-tests. Differences in aberration data between pre- and post-LASIK eyes are then evaluated. The visual acuity prediction using visual Strehl proved to be more accurate for pre-LASIK patients than contrast threshold. However, both methods are comparable for post-LASIK patients.

Field of view of limitations in see-through HMD using geometric waveguides.

Geometric waveguides are being integrated into head-mounted display (HMD) systems, where having see-through capability in a compact, lightweight form factor is required. We developed methods for determining the field of view (FOV) of such waveguide HMD systems and have analytically derived the FOV for waveguides using planar and curved geometries. By using real ray-tracing methods, we are able to show how the geometry and index of refraction of the waveguide, as well as the properties of the coupling optics, impact the FOV. Use of this analysis allows one to determine the maximum theoretical FOV of a planar or curved waveguide-based system.

Evaluation of loss in optical quality of multifocal intraocular lenses with glistenings.

PURPOSE: To study the impact of loss in optical quality from glistenings in diffractive multifocal intraocular lenses (IOLs) using ray tracing in a model eye. SETTING: Independent research laboratory, Irvine, California, USA. DESIGN: Experimental study. METHODS: A pseudophakic eye model was constructed in Zemax, an optical ray-tracing program, using the Arizona eye model as the basis. The Mie scattering theory was used to describe the intensity and direction of light as it scattered for a spherical particle immersed in a diffractive multifocal IOL. To evaluate the impact of glistening scatter, a more advanced eye model was constructed in Fred, a nonsequential optical ray-tracing software. An evaluation of scatter and modulation transfer function (MTF) was performed for a hydrophobic biomaterial with a refractive index of 1.54 for various sizes and densities of glistenings under mesopic conditions. RESULTS: As predicted by the Mie theory, the amount of scatter was a function of the change in the refractive index, size of the scatterer, and volume fraction of the scatterers. This modeling showed that an increase in density of glistenings can lead to a significant drop of MTF of the IOL. This effect was more pronounced in multifocal IOLs than in monofocal IOLs. CONCLUSIONS: Mathematical modeling showed that glistenings in multifocal IOLs lead to a reduction in MTF of the IOL and the pseudophakic eye. The relative loss of MTF in multifocal IOLs was more significant than in monofocal IOLs because of the nature of the design. FINANCIAL DISCLOSURES: Drs. DeHoog and Doraiswamy are consultants to Advanced Vision Science, Inc.

Demonstration of snapshot imaging polarimeter using modified Savart polariscopes.

In an earlier publication, [Appl. Opt.51, 5791 (2012)] we demonstrated by theoretical analysis that a snapshot imaging polarimeter using modified Savart polariscopes (MSP-SIP) is comparable in carrier frequency, signal-to-noise ratio, and spatial resolution to a snapshot imaging polarimeter using conventional Savart polariscopes. In this investigation, numerical simulation is used to demonstrate the feasibility of MSP-SIP and investigate the limitation of the filtration and the Fourier analysis decoupling the polarization information encoded through the spatial modulation. In addition, a laboratory experiment is conducted to demonstrate the validity of MSP-SIP. The MSP-SIP operates on the principle of encoding polarization information within the spatial modulation of the image. This unique technology allows all Stokes parameters to be simultaneously recorded from every spatial position in an image with a single integration period of the imaging system. The device contains no moving parts and requires no scanning, allowing it to acquire data without the motion artifacts normally associated with a scanning polarimeter. In addition to snapshot imaging and static (no moving parts) capabilities, image processing is simple, and the device is compact and miniature. Therefore, we believe that MSP-SIP will be useful in many applications, such as remote sensing and bioscience.

Evaluation of the impact of light scatter from glistenings in pseudophakic eyes.

PURPOSE: To study the impact of light scatter from glistenings in pseudophakic eyes using ray tracing in a model eye SETTING: Department of Research, Advanced Vision Science, Inc., Goleta, California, USA. DESIGN: Mathematical modeling and simulation. METHODS: A pseudophakic eye model was constructed in Zemax using the Arizona eye model as the basis. The Mie scattering theory was used to describe the intensity and direction of light as it scatters for a spherical particle immersed in a given media (intraocular lens [IOL]). The modeling and evaluation of scatter and modulation transfer function (MTF) were performed for several biomaterials with various size and density of glistenings under scotopic, mesopic, and photopic conditions. RESULTS: As predicted by the Mie theory, the amount of scatter was a function of the relative difference in refractive index between the media and the scatterer, the size of the scatterer, and the volume fraction of the scatterer. The simulation demonstrated that an increase in density of glistenings can lead to a significant drop in the MTF of the IOL and the pseudophakic eye. This effect was more pronounced in IOLs with smaller cavitations, and the observation was consistent for all tested biomaterials. CONCLUSIONS: Mathematical modeling demonstrated that glistenings in IOLs will lead to reduction in the MTF of the IOL and the pseudophakic eye. The loss in MTF was more pronounced at high densities and small cavitation sizes across all biomaterials. Inconsistent and poor clinical quantification of glistenings in IOLs may explain some inconsistencies in the literature.

Snapshot imaging polarimeter using modified Savart polariscopes.

In this paper, based on the combination of two modified Savart polariscopes, we present a snapshot imaging polarimeter and show that the carrier frequency is two times higher than that of the snapshot imaging polarimeter using two conventional Savart polariscopes. The signal-to-noise ratio and the spatial resolution of imagery in each channel are improved due to the increase of the carrier frequency when we filter the channels to recover the Stokes vector images. Moreover, compared with conventional imaging polarimetry, the remarkable advantage of the proposed instrument is that it is also simple, compact, miniature, snapshotted, and static (no moving parts). To demonstrate the feasibility of the proposed snapshot imaging polarimeter, the numerical simulation of a design example is presented in detail.

Field-of-view analysis of a polarization interference Fourier transform imaging spectrometer.

The Fourier transform imaging spectrometer (FTIS) is an important tool for the measurement of spectral information in a scene. Advances in electro-optic crystal systems have led to the advent of the FTIS based on polarization interference filters. The operation of these devices as spectrometers has been well characterized, but the imaging capabilities have yet to be thoroughly explored. We explore the field-of-view limitations that occur when using this particular type of FTIS.

Problems testing diffractive intraocular lenses with Shack-Hartmann sensors.

Shack-Hartmann wavefront sensors have found widespread application for testing ocular aberrations. These sensors provide an accurate map of the wavefront emerging from an eye in most cases. However, there is a growing class of patients with diffractive intraocular lenses that will potentially be measured incorrectly with Shack-Hartmann devices. We explore the pitfalls of measuring diffractive lenses with this technology.

Systematic errors analysis for a large dynamic range aberrometer based on aberration theory.

In Ref. 1, it was demonstrated that the significant systematic errors of a type of large dynamic range aberrometer are strongly related to the power error (defocus) in the input wavefront. In this paper, a generalized theoretical analysis based on vector aberration theory is presented, and local shift errors of the SH spot pattern as a function of the lenslet position and the local wavefront tilt over the corresponding lenslet are derived. Three special cases, a spherical wavefront, a crossed cylindrical wavefront, and a cylindrical wavefront, are analyzed and the possibly affected Zernike terms in the wavefront reconstruction are investigated. The simulation and experimental results are illustrated to verify the theoretical predictions.

Systematic error of a large dynamic range aberrometer.

Shack-Hartmann aberrometers are routinely used for measuring ocular aberrations. In one configuration, the intermediate images of the Shack-Hartmann spots formed by the lenslet array are relayed by an imaging lens onto a sensor. A systematic introduction of spherical aberration that is strongly related to the power error (defocus) of the incident wavefront is observed in this configuration. We found that the largest component of this error is induced by the pupil aberration of the imaging relay lens. Some simulations and experimental results are demonstrated.

Snapshot polarimeter fundus camera.

A snapshot imaging polarimeter utilizing Savart plates is integrated into a fundus camera for retinal imaging. Acquired retinal images can be processed to reconstruct Stokes vector images, giving insight into the polarization properties of the retina. Results for images from a normal healthy retina and retinas with pathology are examined and compared.

Fundus camera systems: a comparative analysis.

Retinal photography requires the use of a complex optical system, called a fundus camera, capable of illuminating and imaging the retina simultaneously. The patent literature shows two design forms but does not provide the specifics necessary for a thorough analysis of the designs to be performed. We have constructed our own designs based on the patent literature in optical design software and compared them for illumination efficiency, image quality, ability to accommodate for patient refractive error, and manufacturing tolerances, a comparison lacking in the existing literature.

Compact and miniature snapshot imaging polarimeter.

We present and demonstrate a compact and miniature snapshot imaging polarimeter camera; it is anticipated that such a camera can be scaled down to less than 1.5 cm. Two Savart plates are used at the pupil plane to generate multiple fringes to encode the full Stokes vector in a single image. A geometric ray model is developed to explain the system. The numerical simulation based on this model is presented. Finally, the validity of the device is demonstrated by showing experimental results.