Shape of the anterior surface of the cornea after extended wear of silicone hydrogel soft contact lenses.

PURPOSE: To measure geometrical changes in the anterior surface of the cornea after wearing silicon hydrogel (SiH) soft contact lenses continuously for 1 week. METHODS: Forty-three eyes with 3.0D of myopia and 22 eyes with 3.0D of hyperopia were enrolled in the prospective, interventional study. All subjects underwent a general eye examination, corneal tomography with wavefront aberration analysis, corneal thickness measurements and epithelial thickness mapping before and after wearing SiH lenses (Acuvue Oasys) for 7 days. RESULTS: No significant changes in average keratometry were observed in either refractive group. In the myopic group, keratometry findings for the flat meridian (K1) and central corneal thickness decreased significantly. After +3.0 D lens wear in the hyperopic group, a significant decrease in epithelial thickness up to 3.19 µm was observed in the central and paracentral cornea, (p < 0.001). In both refractive groups, the largest epithelial thickness increase was seen in the periphery. A decrease in spherical aberration was noted in myopic eyes, while an increase of both higher order corneal aberrations and coma was found in hyperopic subjects. CONCLUSION: Extended wear of SiH lenses results in a significant change in epithelial thickness leading to alteration in the geometry of the anterior surface of the cornea, particularly in hyperopic patients. These epithelial thickness variations lead to changes in the higher order aberrations of the cornea.

Automated Bowel Sound Analysis: An Overview.

Despite technological progress, we lack a consensus on the method of conducting automated bowel sound (BS) analysis and, consequently, BS tools have not become available to doctors. We aimed to briefly review the literature on BS recording and analysis, with an emphasis on the broad range of analytical approaches. Scientific journals and conference materials were researched with a specific set of terms (Scopus, MEDLINE, IEEE) to find reports on BS. The research articles identified were analyzed in the context of main research directions at a number of centers globally. Automated BS analysis methods were already well developed by the early 2000s. Accuracy of 90% and higher had been achieved with various analytical approaches, including wavelet transformations, multi-layer perceptrons, independent component analysis and autoregressive-moving-average models. Clinical research on BS has exposed their important potential in the non-invasive diagnosis of irritable bowel syndrome, in surgery, and for the investigation of gastrointestinal motility. The most recent advances are linked to the application of artificial intelligence and the development of dedicated BS devices. BS research is technologically mature, but lacks uniform methodology, an international forum for discussion and an open platform for data exchange. A common ground is needed as a starting point. The next key development will be the release of freely available benchmark datasets with labels confirmed by human experts.

Rapid acousto-optic focus tuning for improvement of imaging performance in confocal microscopy [Invited].

We demonstrate the application of focus-tunable acousto-optic lens technology in confocal microscopy for a high-speed axial scanning of the object. The advantages of the proposed approach include high axial scan rate, no mechanical sample movement, no additional non-symmetric aberrations, and the control of the effective depth of focus. The acousto-optic lens operating at the focus tuning rate of 300 kHz is developed and implemented in scanning laser confocal microscopy. The performance of the instrumentation is presented using test targets. Rapid focus tuning may enhance in vivo three-dimensional imaging in confocal microscopy.

Generation of dynamic Bessel beams and dynamic bottle beams using acousto-optic effect.

We present a novel optical configuration that allows for generation of ultra-high speed dynamic Bessel beams and dynamic bottle beams. The method is based on combination of the axisymmetric acousto-optic device and the spatial filtering enabled by a mask or a digital micromirror device. Selected features of dynamic non-diffracting beams and bottle beams are investigated using time-resolved approach with stroboscopic pulsed illumination, including spatial intensity distribution, spatial modulation factors, MHz-range temporal modulation, and scalability. The numerical simulations based on Fourier optics as well as experimental realizations are demonstrated.

En face enhanced-depth swept-source optical coherence tomography features of chronic central serous chorioretinopathy.

OBJECTIVE: To characterize en face features of the retinal pigment epithelium (RPE) and choroid in eyes with chronic central serous chorioretinopathy (CSCR) using a high-speed, enhanced-depth swept-source optical coherence tomography (SS-OCT) prototype. DESIGN: Consecutive patients with chronic CSCR were prospectively examined with SS-OCT. PARTICIPANTS: Fifteen eyes of 13 patients. METHODS: Three-dimensional 6×6 mm macular cube raster scans were obtained with SS-OCT operating at 1050 nm wavelength and 100000 A-lines/sec with 6 µm axial resolution. Segmentation of the RPE generated a reference surface; en face SS-OCT images of the RPE and choroid were extracted at varying depths every 3.5 µm (1 pixel). Abnormal features were characterized by systematic analysis of multimodal fundus imaging, including color photographs, fundus autofluorescence, fluorescein angiography, and indocyanine-green angiography (ICGA). MAIN OUTCOME MEASURES: En face SS-OCT morphology of the RPE and individual choroidal layers. RESULTS: En face SS-OCT imaging at the RPE level revealed absence of signal corresponding to RPE detachment or RPE loss in 15 of 15 (100%) eyes. En face SS-OCT imaging at the choriocapillaris level showed focally enlarged vessels in 8 of 15 eyes (53%). At the level of Sattler's layer, en face SS-OCT documented focal choroidal dilation in 8 of 15 eyes (53%) and diffuse choroidal dilation in 7 of 15 eyes (47%). At the level of Haller's layer, these same features were observed in 3 of 15 eyes (20%) and 12 of 15 eyes (80%), respectively. In all affected eyes, these choroidal vascular abnormalities were seen just below areas of RPE abnormalities. In 2 eyes with secondary choroidal neovascularization (CNV), distinct en face SS-OCT features corresponded to the neovascular lesions. CONCLUSIONS: High-speed, enhanced-depth SS-OCT at 1050 nm wavelength enables the visualization of pathologic features of the RPE and choroid in eyes with chronic CSCR not usually appreciated with standard spectral domain (SD) OCT. En face SS-OCT imaging seems to be a useful tool in the identification of CNV without the use of angiography. This in vivo documentation of the RPE and choroidal vasculature at variable depths may help elucidate the pathophysiology of disease and can contribute to the diagnosis and management of chronic CSCR.

Microscopic OCT imaging with focus extension by ultrahigh-speed acousto-optic tunable lens and stroboscopic illumination.

We develop high-resolution optical coherence tomography (OCT) system with high-speed acousto-optic tunable lens. Stroboscopic pulsed illumination is used for the first time to perform time-resolved OCT imaging with acousto-optic tunable focusing. The operation of ultrahigh-speed tunable acousto-optic lens is demonstrated theoretically and experimentally. Focal position tuning at MHz frequency range is experimentally shown in the imaging system leading to OCT images with extended depth of focus. Imaging with active optical elements is helpful for improvement of photon collection efficiency, depth of focus and enhancement of the image quality.

Quantitative optical inspection of contact lenses immersed in wet cell using swept source OCT.

We demonstrate swept source optical coherence tomography (OCT) imaging of contact lenses (CLs) in a wet cell and comprehensive quantitative characterization of CLs from volumetric OCT datasets. The approach is based on a technique developed for lens autopositioning and autoleveling enabled by lateral capillary interactions between the wet cell wall and the lens floating on the liquid surface. The demonstrated OCT imaging has enhanced contrast due to the application of a scattering medium and it improves visualization of both CL interfaces and edges. We also present precise and accurate three-dimensional metrology of soft and rigid CLs based on the OCT data. The accuracy and precision of the extracted lens parameters are compared with the manufacturer's specifications. The presented methodology facilitates industrial inspection methods of the CLs.

Reproducibility of a long-range swept-source optical coherence tomography ocular biometry system and comparison with clinical biometers.

OBJECTIVE: To demonstrate a novel swept source optical coherence tomography (SS-OCT) imaging device using a vertical cavity surface-emitting laser (VCSEL) capable of imaging the full eye length and to introduce a method using this device for noncontact ocular biometry. To compare the measurements of intraocular distances using this SS-OCT instrument with commercially available optical and ultrasound biometers. To evaluate the intersession reproducibility of measurements of intraocular distances using SS-OCT. DESIGN: Evaluation of technology. PARTICIPANTS: Twenty eyes of 10 healthy subjects imaged at the New England Eye Center at Tufts Medical Center and Massachusetts Institute of Technology between May and September 2012. METHODS: Averaged central depth profiles were extracted from volumetric SS-OCT datasets. The intraocular distances, such as central corneal thickness (CCT), aqueous depth (AD), anterior chamber depth (ACD), crystalline lens thickness (LT), vitreous depth (VD), and axial length (AL), were measured and compared with a partial coherence interferometry device (IOLMaster; Carl Zeiss Meditec, Inc., Dublin, CA) and an immersion ultrasound (IUS) A-scan biometer (Axis-II PR; Quantel Medical, Inc., Cournon d'Auvergne Cedex, France). MAIN OUTCOME MEASURES: Reproducibility of the measurements of intraocular distances, correlation coefficients, and intraclass correlation coefficients. RESULTS: The standard deviations of the repeated measurements of intraocular distances using SS-OCT were 6 µm (CCT), 16 µm (ACD), 14 µm (AD), 13 µm (LT), 14 µm (VD), and 16 µm (AL). Strong correlations among all 3 biometric instruments were found for AL (r > 0.98). The AL measurement using SS-OCT correlates better with the IOLMaster (r=0.998) than with IUS (r=0.984). The SS-OCT and IOLMaster measured higher AL values than ultrasound (175 and 139 µm, respectively). No statistically significant difference in ACD between the optical (SS-OCT or IOLMaster) and ultrasound methods was detected. High intersession reproducibility of SS-OCT measurements of all intraocular distances was observed with intraclass correlation coefficients >0.99. CONCLUSIONS: The SS-OCT using VCSEL technology enables full eye length imaging and high-precision, noncontact ocular biometry. The measurements with the prototype SS-OCT instrument correlate well with commercial biometers. The SS-OCT biometry has the potential to provide clinically useful comprehensive biometric parameters for pre- and postoperative eye evaluation.

Swept source optical coherence microscopy using a 1310 nm VCSEL light source.

We demonstrate high speed, swept source optical coherence microscopy (OCM) using a MEMS tunable vertical cavity surface-emitting laser (VCSEL) light source. The light source had a sweep rate of 280 kHz, providing a bidirectional axial scan rate of 560 kHz. The sweep bandwidth was 117 nm centered at 1310 nm, corresponding to an axial resolution of 13.1 µm in air, corresponding to 8.1 µm (9.6 µm spectrally shaped) in tissue. Dispersion mismatch from different objectives was compensated numerically, enabling magnification and field of view to be easily changed. OCM images were acquired with transverse resolutions between 0.86 µm - 3.42 µm using interchangeable 40X, 20X and 10X objectives with ~600 µm x 600 µm, ~1 mm x 1 mm and ~2 mm x 2 mm field-of-view (FOV), respectively. Parasitic variations in path length with beam scanning were corrected numerically. These features enable swept source OCM to be integrated with a wide range of existing scanning microscopes. Large FOV mosaics were generated by serially acquiring adjacent overlapping microscopic fields and combining them in post-processing. Fresh human colon, thyroid and kidney specimens were imaged ex vivo and compared to matching histology sections, demonstrating the ability of OCM to image tissue specimens.

High-precision, high-accuracy ultralong-range swept-source optical coherence tomography using vertical cavity surface emitting laser light source.

We demonstrate ultralong-range swept-source optical coherence tomography (OCT) imaging using vertical cavity surface emitting laser technology. The ability to adjust laser parameters and high-speed acquisition enables imaging ranges from a few centimeters up to meters using the same instrument. We discuss the challenges of long-range OCT imaging. In vivo human-eye imaging and optical component characterization are presented. The precision and accuracy of OCT-based measurements are assessed and are important for ocular biometry and reproducible intraocular distance measurement before cataract surgery. Additionally, meter-range measurement of fiber length and multicentimeter-range imaging are reported. 3D visualization supports a class of industrial imaging applications of OCT.

Phase-sensitive swept-source optical coherence tomography imaging of the human retina with a vertical cavity surface-emitting laser light source.

Despite the challenges in achieving high phase stability, Doppler swept-source/Fourier-domain optical coherence tomography (OCT) has advantages of less fringe washout and faster imaging speeds compared to spectral/Fourier-domain detection. This Letter demonstrates swept-source OCT with a vertical cavity surface-emitting laser light source at 400 kHz sweep rate for phase-sensitive Doppler imaging, measuring pulsatile total retinal blood flow with high sensitivity and phase stability. A robust, simple, and computationally efficient phase stabilization approach for phase-sensitive swept-source imaging is also presented.

Age-related changes in geometry and transparency of human crystalline lens revealed by optical signal discontinuity zones in swept-source OCT images.

BACKGROUND: The shape and microstructure of the human crystalline lens alter with ageing, and this has an effect on the optical properties of the eye. The aim of this study was to characterise the age-related differences in the morphology and transparency of the eye lenses of healthy subjects through the optical signal discontinuity (OSD) zones in optical coherence tomography (OCT) images. We also investigated the association of those changes with the optical quality of the eye and visual function. METHODS: OCT images of the anterior segment of 49 eyes of subjects (9-78 years) were acquired, and the OSD zones (nucleus, C1-C4 cortical zones) were identified. Central thickness, curvature and optical density were measured. The eye's optical quality was evaluated by the objective scatter index (OSI). Contrast sensitivity and visual acuity tests were performed. The correlation between extracted parameters and age was assessed. RESULTS: The increase in lens thickness with age was dominated by the thickening of the cortical zone C3 (0.0146 mm/year). The curvature radii of the anterior lens surface and both anterior and posterior nucleo-cortical interfaces decreased with age (- 0.053 mm/year, - 0.013 mm/year and - 0.006 mm/year, respectively), and no change was observed for the posterior lens radius. OCT-based densitometry revealed significant correlations with age for all zones except for C1ß, and the highest increase in density was in the C2-C4 zones (R = 0.45, 0.74, 0.56, respectively, P < 0.001). Increase in OSI was associated with the degradation of visual function. CONCLUSIONS: OCT enables the identification of OSD zones of the crystalline lens. The most significant age-related changes occur in the C3 zone as it thickens with age at a faster rate and becomes more opaque than other OSD zones. The changes are associated with optical quality deterioration and reduction of visual performance. These findings contribute to a better understanding of the structure-function relationship of the ageing lens and offer insights into both pathological and aging alterations.

Swept-source OCT for corneal graft quantitative evaluation in the eye bank and the correlation of the measurements to pre-excision values.

Quantitative evaluation of the human corneal grafts stored in the tissue banks is usually limited to endothelial cell density and central thickness. Swept-source OCT (SS-OCT) is capable of measuring the central curvatures of the corneal tissue prepared for transplantation without loss of sterileness, providing insights on its refractive state. The aim of the paper is to compare in vitro SS-OCT measurements with pre-excision values. Hand-held keratometry and ultrasound pachymetry was performed on 22 corneas before excision of corneoscleral button and insertion in the vial with Eusol-C solution (AlchimiaS.r.l, Nicolò, Italy). After 12 to 36 h of hypothermic storage the corneas were examined within the vials with custom built SS-OCT system maintaining a sterile environment. The anterior and posterior central curvatures, and central corneal thickness (CCT) were measured. Rotation of the corneoscleral button was controlled by making a 6-o'clock mark during excision. Mean pre-excision CCT was 626.45 ± 28.71 µm and 468.05 ± 52.96 µm when measured with SS OCT (r = 0.55; p < 0.001). Respective values for average keratometry were 7.74 ± 0.39 mm and 7.92 ± 0.57 mm (r = 0.6; p = 0.22). Although high differences were observed in corneal thickness, keratometric radius of curvature at the flat (r = 0.42; p < 0.001) and steep (r = 0.62; p = 0.014) meridian of the anterior corneal surface, as well as corneal anterior astigmatism (r = 0.3; p < 0.001), showed good correlation with pre-excision values. SS-OCT is capable of providing quantitative evaluation of the human corneal grafts in hypothermic storage. Good correlation between curvature measurements before excision and during banking in the vial indicates its clinical utility.

Intraocular scatter compensation with spatial light amplitude modulation for improved vision in simulated cataractous eyes.

Cataract is one of the common causes of visual impairment due to opacification of the crystalline lens. Increased intraocular scattering affects the vision of cataract patients by reducing the quality of the retinal image. In this study, an amplitude modulation-based scatter compensation (AM-SC) method is developed to minimize the impact of straylight on the retinal image. The performance of the AM-SC method was quantified by numerical simulations of point spread function and retinal images in the presence of different amounts of straylight. The approach was also experimentally realized in a single-pass system with a digital micro-mirror device used as a spatial amplitude modulator. We showed that the AM-SC method allows to enhance contrast sensitivity in the human eyes in vivo with induced scattering.

Changes in the geometry of modern daily disposable soft contact lenses during wear.

The geometry of contact lenses can be altered by wear but determining the changes that occur in soft contact lenses (SCLs) is challenging. This study aimed to investigate the shape alterations of daily disposable SCLs after wear using swept-source optical coherence tomography (SS-OCT). Forty-five eyes with myopia of - 3.00 diopters (D) were enrolled. The participants wore three types of SCLs: hydrogel lens (nesofilcon A) and silicone hydrogel lenses (delefilcon A and stenfilcon A). The SCLs were scanned 3-6 min after lens removal. We found a significant decrease in the SCL anterior curvature: 0.24 ± 0.17 mm for nesofilcon A, 0.44 ± 0.21 mm for delefilcon A, and 0.53 ± 0.29 mm for stenfilcon A. The changes in the anterior curvature of SCLs correlated moderately with the mean corneal keratometry; Pearson's correlation coefficients for nesofilcon A and delefilcon A were 0.57 and 0.52, respectively (P < 0.001). A statistically significant change in the total diameter was observed in SCL made of stenfilcon A (0.39 mm, P < 0.001). To conclude, the central radii of curvature decreased after a wearing period for all three types of daily disposable SCLs to imitate the anterior corneal surface, however, the changes in other geometrical parameters measured with SS-OCT were lens-specific.

Increased crystalline lens coverage in optical coherence tomography with oblique scanning and volume stitching.

A three-dimensional optical coherence tomography (OCT) crystalline lens imaging method based on oblique scanning and image stitching is presented. The method was designed to increase OCT imaging volume of crystalline lens in vivo. A long-range swept-source (SS)-OCT imaging system, which can measure the entire anterior segment of eye in a single acquisition, is used to acquire one central volume and 4 extra volumes with different angles between optical axis of OCT instrument and the pupillary axis. The volumes are then stitched automatically by developed software. To show its effectiveness and verify its validity, we scanned the subjects before and after pupil dilation drops and compared the experimental results. By determining the number of voxels representing the signal from the crystalline lens in 3-D OCT images, our method can provide around 17% additional volumetric lens coverage compared with a regular imaging procedure. The proposed approach could be used clinically in early diagnosis of cortical cataract. Wider field of view offered by this method may facilitate more accurate lens biometry in its peripheral zones, which potentially contributes to understanding of lens shape modifications of the accommodating eye.

Volumetric Optical Imaging and Quantitative Analysis of Age-Related Changes in Anterior Human Vitreous.

Purpose: The purpose of this study was to characterize age-related changes in anterior human vitreous with 3-D swept source optical coherence tomography (SS-OCT) and evaluate associations with axial length (AL) and contrast sensitivity function (CSF). Methods: There were 49 phakic eyes in 49 patients (40.0 ± 19.3 years) had 3-D volumetric scanning of the lens and retrolental vitreous with SS-OCT at 1050 nm. OCT-derived indices of vitreous optical density (VOD), vitreous opacification ratio (VOR), and lens optical density (LOD) were correlated with AL and double-pass assessment of retinal point spread function (Objective Scatter Index [OSI]). CSF was measured using an adaptive-optics visual simulator (area under log-log contrast sensitivity function [AULCSF]). Results: Vitreous SS-OCT detected gel vitreous, liquefied lacunae, Berger's space, retrolental laminae, and fibrous opacifications. VOD, VOR, and LOD showed high reproducibility (intraclass correlation coefficients 0.968, 0.975, and 0.998, respectively). VOD was highly correlated with VOR (Pearson's R = 0.96, P < 0.000001). VOD, VOR, and LOD correlated with age (R = 0.48, 0.58, and 0.85, P < 0.001 for each). VOR and LOD correlated with OSI (R = 0.36, P = 0.0094, and R = 0.36, P = 0.0096, respectively). VOR correlated negatively with AULCSF (R = -0.53, P < 0.00009), which was related to OSI. Myopic eyes had higher OSI than nonmyopic eyes (P = 0.0121), consistent with correlation between OSI and AL (R = 0.37, P = 0.0091). Multivariable regression confirmed these findings. Conclusions: SS-OCT visualized microstructural features of anterior human vitreous, where opacification is associated with increased light scattering and CSF degradation. SS-OCT enables high-resolution optical evaluation of vitreous opacities.

Whole anterior segment and retinal swept source OCT for comprehensive ocular screening.

Whole eye visualization and morphometry are of high relevance in clinical practice. However, most standard ophthalmic OCT instruments are dedicated either to retinal or to anterior segment imaging. We demonstrate a swept source optical coherence tomography system (SS-OCT) that images both the whole anterior segment and the retina alternately using a single source and detector. A pilot population was imaged with the proof of concept prototype. We demonstrate the clinical potential of whole eye OCT screening for the description and early detection of relevant clinical features in the anterior segment and retina of several patients.

Optical distortion correction in optical coherence tomography for quantitative ocular anterior segment by three-dimensional imaging.

A method for three-dimensional 3-D optical distortion (refraction) correction on anterior segment Optical Coherence Tomography (OCT) images has been developed. The method consists of 3-D ray tracing through the different surfaces, following denoising, segmentation of the surfaces, Delaunay representation of the surfaces, and application of fan distortion correction. The correction has been applied theoretically to realistic computer eye models, and experimentally to OCT images of: an artificial eye with a Polymethyl Methacrylate (PMMA) cornea and an intraocular lens (IOL), an enucleated porcine eye, and a human eye in vivo obtained from two OCT laboratory set-ups (time domain and spectral). Data are analyzed in terms of surface radii of curvature and asphericity. Comparisons are established between the reference values for the surfaces (nominal values in the computer model; non-contact profilometric measurements for the artificial eye; Scheimpflug imaging for the real eyes in vivo and vitro). The results from the OCT data were analyzed following the conventional approach of dividing the optical path by the refractive index, after application of 2-D optical correction, and 3-D optical correction (in all cases after fan distortion correction). The application of 3-D optical distortion correction increased significantly both the accuracy of the radius of curvature estimates and particularly asphericity of the surfaces, with respect to conventional methods of OCT image analysis. We found that the discrepancies of the radii of curvature estimates from 3-D optical distortion corrected OCT images are less than 1% with respect to nominal values. Optical distortion correction in 3-D is critical for quantitative analysis of OCT anterior segment imaging, and allows accurate topography of the internal surfaces of the eye.