Combined high contrast and wide field of view in the scanning laser ophthalmoscope through dual detection of light paths

We demonstrate a multimode detection system in a scanning laser ophthalmoscope (SLO) that enables simultaneous operation in confocal, indirect, and direct modes to permit an agile trade between image contrast and optical sensitivity across the retinal field of view to optimize the overall imaging performance, enabling increased contrast in very wide-field operation. We demonstrate the method on a wide-field SLO employing a hybrid pinhole at its image plane, to yield a twofold increase in vasculature contrast in the central retina compared to its conventional direct mode while retaining high-quality imaging across a wide field of the retina, of up to 200 deg and 20  μm on-axis resolution.

Application of a wide-field phantom eye for optical coherence tomography and reflectance imaging

Optical coherence tomography (OCT) and reflectance imaging are used in clinical practice to measure the thickness and transverse dimensions of retinal features. The recent trend towards increasing the field of view (FOV) of these devices has led to an increasing significance of the optical aberrations of both the human eye and the device. We report the design, manufacture and application of the first phantom eye that reproduces the off-axis optical characteristics of the human eye, and allows the performance assessment of wide-field ophthalmic devices. We base our design and manufacture on the wide-field schematic eye, [Navarro, R. J. Opt. Soc. Am. A, 1985,2.] as an accurate proxy to the human eye and enable assessment of ophthalmic imaging performance for a [Formula: see text] external FOV. We used multi-material 3D-printed retinal targets to assess imaging performance of the following ophthalmic instruments: the Optos 200Tx, Heidelberg Spectralis, Zeiss FF4 fundus camera and Optos OCT SLO and use the phantom to provide an insight into some of the challenges of wide-field OCT.

Compact multi-aperture imaging with high angular resolution

Previous reports have demonstrated that it is possible to emulate the imaging function of a single conventional lens with an N×N array of identical lenslets to provide an N-fold reduction in imaging-system track length. This approach limits the application to low-resolution imaging. We highlight how using an array of dissimilar lenslets, with an array width that can be much wider than the detector array, high-resolution super-resolved imaging is possible. We illustrate this approach with a ray-traced design and optimization of a long-wave infrared system employing a 3×3 array of freeform lenslets to provide a fourfold reduction in track length compared to a baseline system. Simulations of image recovery show that recovered image quality is comparable to that of the baseline system.

Light path-length distributions within the retina

A Monte Carlo simulation of light propagation through the retina has been developed to understand the path-length distributions within the retinal vessel. For full-field illumination, the path-length distribution within the vessel comprises directly backscattered light and light that has passed once or twice through the vessel. The origins of these light path-length distributions can be better understood by investigating different combinations of single-point illumination and detection positions. Perhaps the most significant observation is that illumination at the edges of the vessel, rather than over the whole field of view, and detection directly above the vessel capture only the light that has taken a single pass through the vessel. This path-length distribution is tightly constrained around the diameter of the vessel and can potentially provide enhancements for oxygen saturation imaging. The method could be practically implemented using an offset-pinhole confocal imaging system or structured light illumination.

Multichanneled finite-conjugate imaging

Multichanneled imaging systems rely on nonredundant images recorded by an array of low-resolution imagers to enable construction of a high-resolution image. We show how the varying degree of redundancy associated with imaging throughout the imaged volume effects image quality. Using ray-traced image simulations and a metric used as a proxy for human perception, we show that robust recovery of high-resolution images can be obtained by avoiding excessive redundancy and that this is a felicitous consequence of typical manufacturing tolerances.

Experimental demonstration of continuously variable optical encoding in a hybrid imaging system

We demonstrate an experimental method to obtain a continuously variable hybrid imaging system that uses two generalized cubic phase masks, to enable real-time optimization of the trade between extended depth-of-field and noise gain. We obtain point-spread functions as a function of the rotation angle and show an example of optimization based on recovered image quality.

Infrared imaging with a wavefront-coded singlet lens

We describe the use of wavefront coding for the mitigation of optical aberrations in a thermal imaging system. Diffraction-limited imaging is demonstrated with a simple singlet which enables an approximate halving in length and mass of the optical system compared to an equivalent two-element lens.

Circularly symmetric phase filters for control of primary third-order aberrations: coma and astigmatism

A quartic phase retardation function is described that reduces the variation of the intensity of the focal point of incoherent imaging systems suffering from primary third-order aberrations limited to coma and astigmatism. Corresponding modulation transfer functions are shown to remain practically invariant for moderate amounts of coma and astigmatism.

Decomposition of the optical transfer function: wavefront coding imaging systems

We describe the mapping of the optical transfer function (OTF) of an incoherent imaging system into a geometrical representation. We show that for defocused traditional and wavefront-coded systems the OTF can be represented as a generalized Cornu spiral. This representation provides a physical insight into the way in which wavefront coding can increase the depth of field of an imaging system and permits analytical quantification of salient OTF parameters, such as the depth of focus, the location of nulls, and amplitude and phase modulation of the wavefront-coding OTF.