49 research outputs found

    Polarization Modulation Using Wave Plates to Enhance Foveal Fixation Detection in Retinal Birefringence Scanning for Pediatric Vision Screening Purposes

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    To enhance foveal fixation detection while bypassing the deleterious effects of corneal birefringence in binocular retinal birefringence scanning (RBS) for pediatric vision screening purposes, a new RBS design was developed incorporating a double-pass spinning half wave plate (HWP) combined with a fixed double-pass retarder into the optical system. The spinning HWP enables essential differential polarization detection with only one detector, easing constraints on optical alignment and electronic balancing, and together with a fixed wave plate, this differential RBS signal can be detected essentially independent of various corneal retardances and azimuths. Utilizing the measured corneal birefringence from a dataset of 300 human eyes, an algorithm was developed in MATLAB for optimizing the properties of both wave plates to statistically maximize the RBS signal, while having the greatest independence from left and right eye corneal birefringence. Foveal fixation detection was optimized with the HWP spun 9/16 as fast as the circular scan, with the fixed retarder having a retardance of 45 degrees and fast axis at 90 degrees. Combined with bull's-eye focus detection, this computeroptimized RBS design promises to provide an effective screening instrument for automatic identification of infants at risk for amblyopia, the leading cause of vision loss in childhood

    Matrix approach of Full-Field OCT for volumetric imaging of an opaque human cornea

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    Optical microscopy offers the possibility to image biological tissue with a diffraction limited resolution (~”m). However, the heterogeneity of biological tissues can strongly affect light propagation at large depths by distorting the initial wavefront. Large and short range fluctuations of the refractive index can induce aberration and multiple scattering, respectively. Inspired by a recent work [1], we have developed a matrix approach to Full-Field Optical Coherence Tomography (FF-OCT) to push back the fundamental limit of aberrations and multiple scattering. Here, we report on the application of this approach to the imaging of the human cornea and the quantitative measurement of the corneal transparency. Please click Additional Files below to see the full abstract

    Eye Movements, Strabismus, Amblyopia, and Neuro-Ophthalmology Vertical Vergence Adaptation Produces an Objective Vertical Deviation That Changes With Head Tilt

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    PURPOSE. To document the cyclovertical ocular motor mechanism used for vertical fusion in healthy subjects, and to explore whether vertical vergence training in healthy individuals can produce objectively confirmed vertical deviations that change with head tilt, revealing a basic mechanism that can produce a pattern of misalignment in an otherwise normal ocular motor system that is similar to superior oblique muscle paresis (SOP). METHODS. Seven subjects with normal orthoptic examinations were adapted to vertical image disparities using our tilting haploscopic eye-tracking apparatus presenting concentric circle targets without torsional cues. Static eye positions were recorded with head straight and when tilted 45 degrees to the left and right, during both binocular and monocular viewing. RESULTS. Vertical fusional vergence was accompanied by a cycloversion, with the downwardmoving eye intorting and the upward-moving eye extorting, implicating primary involvement of the oblique extraocular muscles. After adaptation to the slowly increasing vertical target separation, all subjects developed a temporary vertical deviation in the straight ahead position that increased with head tilt to one side and decreased with head tilt to the other side. CONCLUSIONS. These results not only show that head-tilt-dependent changes in vertical deviation are not necessarily pathognomonic for SOP, but also, and more importantly, suggest mechanisms that can mimic SOP and suggest a possible role for vertical vergence training in reducing deviations and thus the amount of head tilt required for fusion. Ultimately, vertical vergence training may provide an adjunct or alternative to extraocular muscle surgery in selected cases

    Fusion Influences the Bielschowsky Head Tilt Test in Superior Oblique Paresis

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    Five patients used the vertical recti for vertical fusional vergence and showed a mean BHTTD - SD of 22.2 - 8.1 PD. After a 30-minute patch test one of those (the only one in whom the test was performed) showed a decrease of 1 PD in BHTTD. Two patients used the "paretic" superior oblique muscle (SOM) and the contralateral superior rectus muscle (SRM) to fuse, and had a mean BHTTD - SD of 5.5 - 7.8 PD. The BHTTD of one of these, in whom a patch test was performed, increased by 11 PD. The remaining patient used the oblique muscles ("paretic" SOM and contralateral inferior oblique muscle (IOM)) to fuse, and showed a BHTTD of only 3 PD, increasing to 21 PD after patching. One explanation for this behavior in the last patient involves lingering vergence adaptation of the "paretic" SOM and contralateral IOM, which makes these muscles more effective when activated on ipsilateral head tilt, lessening the expected increase in hyperdeviation. Similarly, in our two patients with oblique/rectus-mediated fusion, the verge ce-adapted "paretic" SOM and contralateral SRM are activated on ipsilateral and contralateral head tilt respectively, lessening the hyperdeviation in both directions. In the other five patients, however, the vergence-adapted ipsilateral inferior rectus muscle and contralateral SRM are activated on contralateral tilt, possibly accentuating the BHTTD

    Fusion Influences the Bielschowsky Head Tilt Test in Superior Oblique Paresis

    No full text
    Five patients used the vertical recti for vertical fusional vergence and showed a mean BHTTD - SD of 22.2 - 8.1 PD. After a 30-minute patch test one of those (the only one in whom the test was performed) showed a decrease of 1 PD in BHTTD. Two patients used the "paretic" superior oblique muscle (SOM) and the contralateral superior rectus muscle (SRM) to fuse, and had a mean BHTTD - SD of 5.5 - 7.8 PD. The BHTTD of one of these, in whom a patch test was performed, increased by 11 PD. The remaining patient used the oblique muscles ("paretic" SOM and contralateral inferior oblique muscle (IOM)) to fuse, and showed a BHTTD of only 3 PD, increasing to 21 PD after patching. One explanation for this behavior in the last patient involves lingering vergence adaptation of the "paretic" SOM and contralateral IOM, which makes these muscles more effective when activated on ipsilateral head tilt, lessening the expected increase in hyperdeviation. Similarly, in our two patients with oblique/rectus-mediated fusion, the verge ce-adapted "paretic" SOM and contralateral SRM are activated on ipsilateral and contralateral head tilt respectively, lessening the hyperdeviation in both directions. In the other five patients, however, the vergence-adapted ipsilateral inferior rectus muscle and contralateral SRM are activated on contralateral tilt, possibly accentuating the BHTTD

    Higher-order regression three-dimensional motion-compensation method for real-time optical coherence tomography volumetric imaging of the cornea

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    International audienceSignificance: Optical coherence tomography (OCT) allows high-resolution volumetric three-dimensional (3D) imaging of biological tissues in vivo. However, 3D-image acquisition can be time-consuming and often suffers from motion artifacts due to involuntary and physiological movements of the tissue, limiting the reproducibility of quantitative measurements.Aim: To achieve real-time 3D motion compensation for corneal tissue with high accuracy.Approach: We propose an OCT system for volumetric imaging of the cornea, capable of compensating both axial and lateral motion with micron-scale accuracy and millisecond-scale time consumption based on higher-order regression. Specifically, the system first scans three reference B-mode images along the C-axis before acquiring a standard C-mode image. The difference between the reference and volumetric images is compared using a surface-detection algorithm and higher-order polynomials to deduce 3D motion and remove motion-related artifacts.Results: System parameters are optimized, and performance is evaluated using both phantom and corneal (ex vivo) samples. An overall motion-artifact error of <4.61 microns and processing time of about 3.40 ms for each B-scan was achieved.Conclusions: Higher-order regression achieved effective and real-time compensation of 3D motion artifacts during corneal imaging. The approach can be expanded to 3D imaging of other ocular tissues. Implementing such motion-compensation strategies has the potential to improve the reliability of objective and quantitative information that can be extracted from volumetric OCT measurements

    Blind speckle illumination for aberration correction

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    International audienceWe propose a computational optical technique based on speckle-pattern illumination of an object and a gradient descent algorithm, enabling aberration correction without requiring the addition of adaptive optics

    Quantitative measures of corneal transparency, derived from objective analysis of depth-resolved corneal images, demonstrated with full-field optical coherence tomographic microscopy

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    International audienceLoss of corneal transparency, as occurs with various pathologies, infections, immune reactions, trauma, aging, and surgery, is a major cause of visual handicap worldwide. However, current means to assess corneal transparency are extremely limited and clinical and eye-bank practice usually involve a subjective and qualitative observation of opacities, sometimes with comparison against an arbitrary grading scale, by means of slit-lamp biomicroscopy. Here, we describe a novel objective optical data analysis-based method that enables quantifiable and standardized characterization of corneal transparency from depth-resolved corneal images, addressing the demand for such a means in both the laboratory and clinical ophthalmology setting. Our approach is based on a mathematical analysis of the acquired optical data with respect to the light attenuation from scattering processes in the corneal stroma. Applicable to any depth-resolved corneal imaging modality, it has been validated by means of full-field optical coherence tomographic microscopy (FF-OCT or FF-OCM). Specifically, our results on ex-vivo corneal specimens illustrate that 1) in homogeneous tissues, characterized by an exponential light attenuation with stromal depth (z), the computation of the scattering mean-free path (ls) from the rate of exponential decay allows quantification of the degree of transparency; 2) in heterogeneous tissues, identified by significant deviations from the normal exponential z -profile, a measure of exponential-decay model inadequacy (e.g., by computation of the Birge ratio) allows the estimation of severity of stromal heterogeneity, and the associated depth-dependent variations around the average ls enables precise localization of the pathology
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