4D Light FIeld Ophthalmoscope: A Study of Plenoptic Imaging for Retinal Imaging

The application of 4D Light Field technique to retinal imaging is proposed as a multi- modality imaging device. A feasibility study developed with numerical simulations is presente

Structured illumination microscopy for in-vivo human retinal imaging: a theoretical assessment

Structured illumination microscopy applied to in-vivo retinal imaging has the potential to provide a low-cost and powerful diagnostic tool for retinal disease. In this paper the key parameters that affect performance in structured illumination ophthalmoscopy are studied theoretically. These include the number of images that need to be acquired in order to generate a sectioned image, which is affected by the non-stationary nature of the retina during acquisition, the choice of spatial frequency of the illuminating sinusoid, the effect of typical ocular aberrations on axial resolution and the nature of the sinusoidal pattern produced by the illumination system. The results indicate that structured illumination ophthalmoscopy can be a robust technique for achieving axial sectioning in retinal imaging without the need for complex optical systems

Study of the dynamic tear film aberrations using a curvature sensing setup

The advancement in adaptive optics in recent years has increased the interest in the dynamic aberrations of the eye, including those introduced by the first optical surface provided by the tear film. A curvature sensing system to measure the dynamic topography of the tear film is described. This optical system was used to measure the aberrations of the tear film on 14 eyes. The evolution of this surface is monitored through videos of the tear film topography. The effect on optical quality is studied from the time-evolution of the RMS wavefront error showing non-negligible aberration variations attributed to the tear film layer; the effect of tear film break-up on the ocular optical quality is also discussed. Furthermore, the aberration maps are decomposed into their constituent Zernike components showing stronger contributions from 4th order terms, and also from those components with vertical symmetry which can be attributed to the effect of the eye lids on the tear film. Finally, the power spectra of the RMS wavefront error evolution show that the strongest contributions of the tear film aberrations are to be found at low frequencies, typically below 2Hz

Differential amplitude scanning for retinal imaging: a theoretical study

A differential amplitude scanning system for ophthalmoscopy is described theoretically. The differential scanning ophthalmoscope (DSO) samples the retina with two laterally displaced spots. The signal measured is the difference between the irradiance from these two locations. The theoretical analysis of the DSO shows it offers increased contrast at high spatial frequencies and only weak contributions from the low frequencies. This enables high-gain, low-noise detection that maximizes contrast

New methodology to measure the dynamics of ocular wave front aberrations during small amplitude changes of accommodation

We present a methodology to measure the systematic changes of aberrations induced by small changes in amplitude of accommodation. We use a method similar the one used in electrophysiology, where a periodic stimulus is presented to the eye and many periods (epochs) of the stimulus are averaged. Using this technique we have measured changes in higher order aberrations from 0.006μm to 0.02μm and correlated them with amplitude changes of accommodation as small as 0.14D. These small changes would have been undetectable without epoch averaging. The correlation coefficients of Zernike terms with defocus were calculated, demonstrating higher values of correlation for epoch averaging. The accurate monitoring of defocus at the start of the accommodation response has shown some interesting trends that may be related with the mechanisms behind accommodation

Curvature sensor for the measurement of the static corneal topography and the dynamic tear film topography in the human eye

A system to measure the topography of the first optical surface of the human eye noninvasively by using a curvature sensor is described. The static corneal topography and the dynamic topography of the tear film can both be measured, and the topographies obtained are presented. The system makes possible the study of the dynamic aberrations introduced by the tear film to determine their contribution to the overall ocular aberrations in healthy eyes, eyes with corneal pathologies, and eyes wearing contact lenses

Lipodystrophy : focus on HIV Lipodystrophy

Lipodystrophy is a rare condition which can be inherited or acquired, localised or generalised. It is characterised by abnormal adipose tissue distribution and in some cases underlying metabolic derangement, including diabetes mellitus, hypertriglyceridemia, hepatic steatosis, polycystic ovaries and acanthosis nigricans. Today, most cases of lipodystrophy are associated with human immunodeficiency virus (HIV). This article gives a review of the possible mechanisms associated with HIV lipodystrophy, namely HIV infection itself, genetic susceptibility to HIV lipodystrophy and effects of treatment with highly active antiretroviral therapy (HAART). Treating HIV lipodystrophy is challenging. The various treatment options currently available for treating lipodystrophy are reviewed.peer-reviewe