Complete polarization and phase control for focus-shaping in high-NA microscopy.

We show that, in order to attain complete polarization control across a beam, two spatially resolved variable retardations need to be introduced to the light beam. The orientation of the fast axes of the retarders must be linearly independent on the Poincaré sphere if a fixed starting polarization state is used, and one of the retardations requires a range of 2π. We also present an experimental system capable of implementing this concept using two passes on spatial light modulators (SLMs). A third SLM pass can be added to control the absolute phase of the beam. Control of the spatial polarization and phase distribution of a beam has applications in high-NA microscopy, where these properties can be used to shape the focal field in three dimensions. We present some examples of such fields, both theoretically calculated using McCutchen's method and experimentally observed.

High resolution wavefront correction with photocontrolled deformable mirror.

We demonstrate that a novel actuation scheme, employed in an optical control deformable mirror, can be more convenient than the conventional discrete fixed actuators approach. The Photo-Controlled Deformable Mirror (PCDM) mirror leverages consumer LCD display technology in the wavefront forming control, enabling flexible programmable configuration of the actuation geometry. This new approach simplifies the driving electronics, relaxing the per channel cost of high spatial control of the wavefront forming surface. In our experiment we tested the PCDM by applying the equivalent of 36, 76 and 201 actuators, this by just changing the light driving pattern. We demonstrated the effectiveness of this technique in a closed loop setup, which showed performances superior to the state of the art for similar DM, while providing a significant reduction in the hardware complexity.

A non-stationary model for simulating the dynamics of ocular aberrations.

The time-evolution of ocular aberrations has been the subject of many studies, but so far there has been little discussion involving the modelling of the underlying temporal statistics. This paper presents a non-stationary modelling approach based on a coloured-noise generator, which can be applied to ocular aberration dynamics. The model parameters are computed from measured ocular aberration data. A custom-built aberrometer based on a Shack-Hartmann sensor was used for measurement. We present simulations based on our modelling approach, and validate them through comparison to real data. This work could be useful in areas such as the testing of ophthalmic devices and the development of improved algorithms for laser refractive surgery.

Temporal dynamics and statistical characteristics of the microfluctuations of accommodation: dependence on the mean accommodative effort.

Microfluctuations of accommodation have been the subject of many studies. New technological developments now permit us to study the dynamics of the microfluctuations with unprecedented resolution and accuracy. We aim to characterise their temporal statistics for different levels of accommodative effort, using a custom-built aberrometer. We conducted 46 s long measurements on the dominant eye of 9 young, healthy subjects. The ocular wavefront was sampled every 250 microm across the 3.9 mm measured pupil, at a frame rate of 173 Hz. This enabled us to obtain high resolution estimates of the Power Spectral Density (PSD). Results show that the shape of the estimated PSD for a 4 D effort is distinct from the shape for the two extrema of the accommodation range. The autocorrelation function of the increments of the accommodation signal is also affected by the level of effort, regardless of the refractive error of the subject.

Estimation of centroid positions with a matched-filter algorithm: relevance for aberrometry of the eye.

Most Shack-Hartmann based aberrometers use infrared light, for the comfort of the patients. A large amount of the light that is scattered from the retinal layers is recorded by the detector as background, from which it is not trivial to estimate the centroid of the Shack-Hartmann spot. For a centroiding algorithm, background light can lead to a systematic bias of the centroid positions towards the centre of the software window. We implement a matched filter algorithm for the estimation of the centroid positions of the Shack-Hartmann spots recorded by our aberrometer. We briefly present the performance of our algorithm, and recall the well-known robustness of the matched filter algorithm to background light. Using data collected on 5 human eyes, we parameterise a simple and fast centroiding algorithm and reduce the difference between the two algorithms down to a mean residual wavefront of 0.02 microm rms.

A simple and robust method to extend the dynamic range of an aberrometer.

We present an algorithm to extend significantly the dynamic range of a Shack-Hartmann wavefront sensor. With this method, the recorded Shack-Hartmann spots are not constrained to stay in the field of view of their lenslet. The proposed algorithm is computationally effective, robust to a high level of noise on the measured centroid positions and also to missing centroid values. The principle is closely related to the description of wavefronts using Zernike polynomials, which makes optimization for a given sensor and application achievable thanks to numerical simulation. These features make it useful for the measurements of highly aberrated eyes.

The reality of treating dyslipidaemia in patients with coronary heart disease: a primary care survey.

Management of hyperlipidaemia in patients with ischaemic heart disease is suboptimal despite the proven benefit of statin therapy. Significant improvement in management has been shown in the EUROASPIRE II study. It is unclear, however, whether such changes have also occurred in primary care. We aimed to evaluate the use of statin therapy by performing a cross-sectional survey of 300 patients with CHD aged >30 years from three general practices. A total of 249 (83%) of the 300 patients had their cholesterol measured and 141 (47%) were on statin therapy; 129 (43% of total) achieved a target cholesterol of <5 mmol/l, of whom 85 (64%) were on statin therapy. Of the remaining 120 patients whose cholesterol exceeded 5 mmol/l, 56 (47%) were on statin therapy Thus 60% (85/141) of those on statin therapy achieved adequate control compared with 40% (44/108) without statins (p<0.008). Those patients with CHD diagnosed on objective evidence were more likely to receive statin therapy (55.5%). Many patients with CHD are still not receiving appropriate secondary prevention. Those on statin therapy are more likely to achieve target levels <5 mmol/l. The average doses of statins vary and are lower than the evidence-based doses used in previous large-scale studies, which may help explain the persistence of failed treatment.