Adaptive Optics Scanning Ophthalmoscopy with Annular Pupils

Annular apodization of the illumination and/or imaging pupils of an adaptive optics scanning light ophthalmoscope (AOSLO) for improving transverse resolution was evaluated using three different normalized inner radii (0.26, 0.39 and 0.52). In vivo imaging of the human photoreceptor mosaic at 0.5 and 10° from fixation indicates that the use of an annular illumination pupil and a circular imaging pupil provides the most benefit of all configurations when using a one Airy disk diameter pinhole, in agreement with the paraxial confocal microscopy theory. Annular illumination pupils with 0.26 and 0.39 normalized inner radii performed best in terms of the narrowing of the autocorrelation central lobe (between 7 and 12%), and the increase in manual and automated photoreceptor counts (8 to 20% more cones and 11 to 29% more rods). It was observed that the use of annular pupils with large inner radii can result in multi-modal cone photoreceptor intensity profiles. The effect of the annular masks on the average photoreceptor intensity is consistent with the Stiles-Crawford effect (SCE). This indicates that combinations of images of the same photoreceptors with different apodization configurations and/or annular masks can be used to distinguish cones from rods, even when the former have complex multi-modal intensity profiles. In addition to narrowing the point spread function transversally, the use of annular apodizing masks also elongates it axially, a fact that can be used for extending the depth of focus of techniques such as adaptive optics optical coherence tomography (AOOCT). Finally, the positive results from this work suggest that annular pupil apodization could be used in refractive or catadioptric adaptive optics ophthalmoscopes to mitigate undesired back-reflections

Non-common Path Aberration Correction in an Adaptive Optics Scanning Ophthalmoscope

The correction of non-common path aberrations (NCPAs) between the imaging and wavefront sensing channel in a confocal scanning adaptive optics ophthalmoscope is demonstrated. NCPA correction is achieved by maximizing an image sharpness metric while the confocal detection aperture is temporarily removed, effectively minimizing the monochromatic aberrations in the illumination path of the imaging channel. Comparison of NCPA estimated using zonal and modal orthogonal wavefront corrector bases provided wavefronts that differ by ~λ/20 in root-mean-squared (~λ/30 standard deviation). Sequential insertion of a cylindrical lens in the illumination and light collection paths of the imaging channel was used to compare image resolution after changing the wavefront correction to maximize image sharpness and intensity metrics. Finally, the NCPA correction was incorporated into the closed-loop adaptive optics control by biasing the wavefront sensor signals without reducing its bandwidth

First-order Design of a Reflective Viewfinder for Adaptive Optics Ophthalmoscopy

Adaptive optics (AO) ophthalmoscopes with small fields of view have limited clinical utility. We propose to address this problem in reflective instruments by incorporating a viewfinder pupil relay designed by considering pupil and image centering and conjugation. Diverting light from an existing pupil optical relay to the viewfinder relay allows switching field of view size. Design methods that meet all four centering and conjugation conditions using either a single concave mirror or with two concave mirrors forming an off-axis afocal telescope are presented. Two different methods for calculating the focal length and orientation of the concave mirrors in the afocal viewfinder relay are introduced. Finally, a 2.2 × viewfinder mode is demonstrated in an AO scanning light ophthalmoscope

\u3cem\u3eIn vivo\u3c/em\u3e Dark-field Imaging of the Retinal Pigment Epithelium Cell Mosaic

Non-invasive reflectance imaging of the human RPE cell mosaic is demonstrated using a modified confocal adaptive optics scanning light ophthalmoscope (AOSLO). The confocal circular aperture in front of the imaging detector was replaced with a combination of a circular aperture 4 to 16 Airy disks in diameter and an opaque filament, 1 or 3 Airy disks thick. This arrangement reveals the RPE cell mosaic by dramatically attenuating the light backscattered by the photoreceptors. The RPE cell mosaic was visualized in all 7 recruited subjects at multiple retinal locations with varying degrees of contrast and cross-talk from the photoreceptors. Various experimental settings were explored for improving the visualization of the RPE cell boundaries including: pinhole diameter, filament thickness, illumination and imaging pupil apodization, unmatched imaging and illumination focus, wavelength and polarization. None of these offered an obvious path for enhancing image contrast. The demonstrated implementation of dark-field AOSLO imaging using 790 nm light requires low light exposures relative to light safety standards and it is more comfortable for the subject than the traditional autofluorescence RPE imaging with visible light. Both these factors make RPE dark-field imaging appealing for studying mechanisms of eye disease, as well as a clinical tool for screening and monitoring disease progression

An Overview of Nigeria Information Policy

An information policy for Nigeria is most desirable in the face of the emergence of an information society. The purpose of this paper is to present a scenario of information activities in the various bodies responsible for information services especially in the public sector. The paper also believes that national policy on information can be traced amongst the various bodies involved with information production and distribution. Samaru Journal of Information Studies Vol. 7 (1) 2007: pp. 8-1

Convergence rates for variational regularization of inverse problems in exponential families

We consider statistical inverse problems with statistical noise. By using regularization methods one can approximate the true solution of the inverse problem by a regularized solution. The previous investigation of convergence rates for variational regularization with Poisson and empirical process data is shown to be suboptimal. In this thesis we obtain improved convergence rates for variational regularization methods of nonlinear ill-posed inverse problems with certain stochastic noise models described by exponential families and derive better reconstruction error bounds by applying deviation inequalities for stochastic process in some function spaces. Furthermore, we also consider iteratively regularized Newton-method as an alternative while the operator is non-linear. Due to the difficulty of deriving suitable deviation inequalities for stochastic processes in some function spaces, we are currently not able to obtain optimal convergence rates for variational regularization such that we state our desired result as a conjecture. If our conjecture holds true, then we can immediately obtain our desired results

Opinion: Early diagnosis of Breast Cancer

Cancer of the breast is the commonest malignant disease in women. It is a major public health problem worldwide. The cause is unknown, but there are documented risk factors. Most of the patients are symptomatic at the time of detection. A breast lump is by far the most common and the only symptom in majority of patients. The diagnosis is made from physical examination, imaging, cytology and biopsy. Key Words: Breast cancer, early diagnosis Annals of African Medicine Vol.3(2) 2004: 95-9

Contemporary Security Challenges and Its Effects on Nigeria’s Foreign Relations, 2015-2022

The nefarious activities of Boko Haram terrorists, armed bandits, herders-farmers clashes and Indigenous People of Biafra (IPOB) among others have devastating effects on Nigeria’s national security. Efforts by the federal government at curtailing their activities notwithstanding, these criminal elements have continued to operate with impunity; killing, maiming and raping of innocent citizens across the country. Boko Haram terrorists mostly operate in the North-East Region while armed herders violently attack sedentary crop farmers in the North-Central; the North-West and South-East Regions have been riddled by the activities of armed bandits and IPOB members respectively. Consequently, the security situation in the country is deteriorating with debilitating consequences on her foreign relations. Relying on exegesis of relevant secondary sources such as books, journals, newspapers and web-based materials among others; the paper posits that the nefarious activities of Boko Haram terrorists, armed bandits, IPOB members and violent herders among other criminal elements threatens Nigeria’s national security, which by extension affects her foreign relations. The paper concludes that the country’s security situation may further deteriorate as long as the government keeps politicizing insecurity in the country. The paper therefore recommends, among other things, that the government should stop politicizing insecurity and stand up to its primary responsibility of securing the lives and property of its citizens while at the same time delivering dividends of democracy in an atmosphere of good governance characterized by freedom, equity and justice

Assessment of Information Sources and Services Provided for the Business Needs of the Micro and Small Scale Enterprises in North West Zone, Nigeria.

Business information consists of every factor influential to business operation. It is influenced by a set of political, economic, social and technological factors which are largely outside the control and influence of a business. The general objective of this study was to investigate into business information sources and services of micro and small business enterprises in the North-West geo-political zone of Nigeria. The survey research method was adopted for the study. From the parent population of micro and small business enterprises, seven municipal areas of the geopolitical zone were randomly sampled. Research instrument used for collecting data was the questionnaire which was constructed along the theoretical frame of the study. Hypotheses were formulated to provide basis for inferences from the analysed data. The findings showed that the effective provision of business information towards the need of small business enterprises requires more articulated services to fill the existing gap. Significant correlation was observed between the entrepreneurs’ awareness of required information for their business and their access to such information. It was observed that accessibility of business information is significantly related to availability of the information, the awareness and visibility of sources and services