Astigmatism and Pseudoaccommodation in Pseudophakic Eyes

noAdvanced IOLs with circumferential zones of different power provide pseudoaccommodation. We investigated the potential for power variation with meridian, namely astigmatism, to provide pseudo-accommodation. With appropriate power and axis orientations, acceptable pseudo-accommodation can be achieved

Non-contact video-based assessment of the respiratory function using a RGB-D camera

A fully automatic, non-contact method for the assessment of the respiratory function is proposed using an RGB-D camera-based technology. The proposed algorithm relies on the depth channel of the camera to estimate the movements of the body’s trunk during breathing. It solves in fixed-time complexity, O(1), as the acquisition relies on the mean depth value of the target regions only using the color channels to automatically locate them. This simplicity allows the extraction of real-time values of the respiration, as well as the synchronous assessment on multiple body parts. Two different experiments have been performed: a first one conducted on 10 users in a single region and with a fixed breathing frequency, and a second one conducted on 20 users considering a simultaneous acquisition in two regions. The breath rate has then been computed and compared with a reference measurement. The results show a non-statistically significant bias of 0.11 breaths/min and 96% limits of agreement of -2.21/2.34 breaths/min regarding the breath-by-breath assessment. The overall real-time assessment shows a RMSE of 0.21 breaths/min. We have shown that this method is suitable for applications where respiration needs to be monitored in non-ambulatory and static environments.This research was funded by Ministerio de Ciencia e Innovación with grant number PID2020-116011.Postprint (published version

Aerospace Medicine and Biology: A continuing bibliography with indexes (supplement 258)

This bibliography lists 308 reports, articles and other documents introduced into the NASA scientific and technical information system in April 1984

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 128, May 1974

This special bibliography lists 282 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1974

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 267, January 1985

This publication is a cumulative index to the abstracts contained in the Supplements 255 through 266 of Aerospace Medicine and Biology: A Continuing Bibliography. It includes seven indexes--subject, personal author, corporate source, foreign technology, contract number, report number, and accession number

Biomechanical aspects of the anterior segment in human myopia

The thesis investigates the relationship between the biomechanical properties of the anterior human sclera and cornea in vivo using Schiotz tonometry (ST), rebound tonometry (RBT, iCare) and the Ocular Response Analyser (ORA, Reichert). Significant differences in properties were found to occur between scleral quadrants. Structural correlates for the differences were examined using Partial Coherent Interferometry (IOLMaster, Zeiss), Optical Coherent tomography (Visante OCT), rotating Scheimpflug photography (Pentacam, Oculus) and 3-D Magnetic Resonance Imaging (MRI). Subject groups were employed that allowed investigation of variation pertaining to ethnicity and refractive error. One hundred thirty-five young adult subjects were drawn from three ethnic groups: British-White (BW), British-South-Asian (BSA) and Hong-Kong-Chinese (HKC) comprising non-myopes and myopes. Principal observations: ST demonstrated significant regional variation in scleral resistance a) with lowest levels at quadrant superior-temporal and highest at inferior-nasal; b) with distance from the limbus, anterior locations showing greater resistance. Variations in resistance using RBT were similar to those found with ST; however the predominantly myopic HKC group had a greater overall mean resistance when compared to the BW-BSA group. OCT-derived scleral thickness measurements indicated the sclera to be thinner superiorly than inferiorly. Thickness varied with distance from the corneolimbal junction, with a decline from 1 to 2 mm followed by a successive increase from 3 to 7 mm. ORA data varied with ethnicity and refractive status; whilst axial length (AL) was associated with corneal biometrics for BW-BSA individuals it was associated with IOP in the HKC individuals. Complex interrelationships were found between ORA Additional-Waveform-Parameters and biometric data provided by the Pentacam. OCT indicated ciliary muscle thickness to be greater in myopia and more directly linked to posterior ocular volume (from MRI) than AL. Temporal surface areas (SAs, from MRI) were significantly smaller than nasal SAs in myopic eyes; globe bulbosity (from MRI) was constant across quadrants

Use of OCT and Oculus Pentacam HR as Aids to Semi-Scleral Contact Lens Fitting

Purpose: To determine whether semi-scleral contact lenses (sSCL) can be appropriately fitted using corneal sagittal depth measurements, and to determine the impact of fit on visual acuity, effect of time on topographic corneal clearance and comfort ratings. Method: Three sSCL (Jupiter 15mm; Essilor) were fit to 20 subjects who had previous diagnoses of KC (n=18) or PMD (n=2). The fitting of the sSCL were based on the CSD measured with the Visante™ OCT at a 15mm chord on the horizontal meridian. To select the sSCL from the diagnostic trial lens set, values of 325 (lens 1), 375 (lens 2) and 425 (lens 3) μm were randomly added in sequence to the CSD. Subjects were allowed to wear each of the sSCL for 1hour. After this time, the central corneal clearance (CCC) was assessed using an UL-OCT, high contrast visual acuity (HCVA) and low contrast visual acuity (LCVA) were measured using a LogMAR VA chart and comfort ratings were obtained using a comfort rating scale (0-100). Results: The mean CSD in the horizontal meridian was 3.78±0.53 (range: 3.33-4.17) mm at a 15mm chord. The mean CCC was 190±100, 360±120 and 450±170 µm for each lens respectively (p=0.001). The mean CCC loss was 30.00±40.00, 30±60.00 and 40.00±50 µm for each lens respectively (p>0.05). The mean HCVA for lenses 1, 2 and 3 were 0.05±0.12, 0.07±0.11 and 0.11±0.08 respectively, which were significantly different (p=0.02). Tukey post hoc analysis demonstrated that this difference was only significant between lenses 1 and 3 (p=0.01). Similar findings were found for LCVA. The overall comfort rating for all three sSCL was 77.7±10.6. The comfort ratings for lenses 1, 2 and 3 were 74.9±9.2, 79.7 ±11.6 and 78.6±10.8 respectively. These differences were not significantly different (p=0.24). Conclusion: Evaluation of CSD can be used effectively to select which sSCL to fit on the eye. The results of this study suggest that lens 2 (adding 375 μm to the CSD) gave the best combination of VA and comfort ratings. However, evaluation of the fluorescein pattern must be balanced with the VA and comfort ratings for successful fitting of sSCL in a clinical setting. There was also a likelihood of topographic corneal loss after 1 hour of sSCL wear; however, this may vary depending on many factors such as scleral zone and its relationship with the scleral conjunctiva. Eyelid force, design of the contact lens and other unknown factors may play a part in the contact lens settling time and amount

In vivo microvascular oximetry using multispectral imaging

This thesis describes the application of multispectral imaging to several novel oximetry applications. Chapter 1 motivates optical microvascular oximetry, outlines oxygen transport in the body, describes the theory of oximetry, and describes the challenges associated with in vivo oximetry, in particular imaging through tissue. Chapter 2 reviews various imaging techniques for quantitative in vivo oximetry of the microvasculature, including multispectral and hyperspectral imaging, photoacoustic imaging, optical coherence tomography, and laser speckle techniques. Chapter 3 describes a two-wavelength oximetry study of two microvascular beds in the anterior segment of the eye: the bulbar conjunctival and episcleral microvasculature. This study reveals previously unseen oxygen diffusion from ambient air into the bulbar conjunctival microvasculature, altering the oxygen saturation of the bulbar conjunctiva. The response of the bulbar conjunctival and episcleral microvascular beds to acute mild hypoxia is quantified and the rate at which oxygen diffuses into bulbar conjunctival vessels is measured. Chapter 4 describes the development and application of a highly novel non-invasive retinal angiography technique: Oximetric Ratio Contrast Angiography (ORCA). ORCA requires only multispectral imaging and a small perturbation of blood oxygen saturation to produce angiographic sequences. A pilot study of ORCA in human subjects was conducted. This study demonstrates that ORCA can produce angiographic sequences with features such as sequential vessel filling and laminar flow. The application and challenges of ORCA are discussed, with emphasis on comparison with other angiography techniques, such as fluorescein angiography. Chapter 5 describes the development of a multispectral microscope for oximetry in the spinal cord dorsal vein of rats. Measurements of blood oxygen saturation are made in the dorsal vein of both healthy rats, and in rats with the Experimental autoimmune encephalomyelitis (EAE) disease model of multiple sclerosis. The venous blood oxygen saturation of EAE disease model rats was found to be significantly lower than that of healthy controls, indicating increased oxygen uptake from blood in the EAE disease model of multiple sclerosis. Chapter 6 describes the development of video-rate red eye oximetry; a technique which could enable stand-off oximetry of the blood-supply of the eye with high temporal resolution. The various challenges associated with video-rate red eye oximetry are investigated and their influence quantified. The eventual aim of this research is to track circulating deoxygenation perturbations as they arrive in both eyes, which could provide a screening method for carotid artery stenosis, which is major risk-factor for stroke. However, due to time constraints, it was not possible to thoroughly investigate if video-rate red eye can detect such perturbations. Directions and recommendations for future research are outlined