Adaptive optics (AO) enables imaging of cellular structures in the retina that are not visible with clinical imaging techniques, providing the potential for earlier detection of retinal disease and enhanced monitoring of progression. The aim of this work was to develop automated, quantitative techniques for characterizing the morphology of the posterior retina in AO-OCT B-scans. Images were obtained from a custom-built dual-modality AO-optical coherence tomographyscanning laser ophthalmoscopy (AO-OCT-SLO) imaging system. Automated segmentation and cone identification procedures were developed and applied to images from two groups: healthy controls and dry age-related macular degeneration (AMD) subjects. Results from the automated routines were compared to measurements made manually by an expert human reviewer, demonstrating good agreement. Results from the control subjects showed decreasing cone inner and outer segment lengths with increasing distance from the fovea. The cone outer segment tip (COST) layer had a greater variation in axial position compared to the inner segment/outer segment (IS/OS) junction. Results from the AMD group indicate that disruption in the COST layer over drusen occurs earlier and to a greater extent than the IS/OS junction, which may be useful in the detection of emerging drusen.
We have designed and implemented a dual-mode adaptive optics (AO) imaging system that combines spectral domain optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO) for in vivo imaging of the human retina. The system simultaneously acquires SLO frames and OCT B-scans at 60 Hz with an OCT volume acquisition time of 4.2 s. Transverse eye motion measured from the SLO is used to register the OCT B-scans to generate three-dimensional (3-D) volumes. Key optical design considerations include: minimizing system aberrations through the use of off-axis relay telescopes, conjugate pupil plane requirements, and the use of dichroic beam splitters to separate and recombine the OCT and SLO beams around the nonshared horizontal scanning mirrors. To demonstrate system performance, AO-OCT-SLO images and measurements are taken from three normal human subjects ranging in retinal eccentricity from the fovea out to 15-deg temporal and 20-deg superior. Also presented are en face OCT projections generated from the registered 3-D volumes. The ability to acquire high-resolution 3-D images of the human retina in the midperiphery and beyond has clinical importance in diseases, such as retinitis pigmentosa and cone–rod dystrophy.
Combined adaptive optics (AO) optical coherence tomography (OCT) scanning laser ophthalmoscopy (SLO) imaging
allows simultaneous en face and cross sectional views of the retina. We describe improvements to our AO-OCT-SLO
system and highlight its resolution capability and clinical utility by presenting results from 3 control and 4 dry agerelated
macular degeneration (AMD) subjects. From a group of subjects with healthy eyes, OCT A-scans were grouped
as originating from cones or rods and were averaged. The resulting reflectance profiles were then used to identify the
location of cone and rod segments. Results for rods and cones were compared, with the focus on inner segment (IS) and
outer segment (OS) structures and where these cells embed into the retinal pigment epithelium (RPE). In the AMD
patients, cone IS and OS lengths were measured over and around drusen for two retinal regions (fovea–2° and 2°–4°),
and those results were correlated to drusen height. For the fovea–2° region, the drusen height that caused statistically
significant shortening of cone ISL and OSL compared to the unaffected adjacent area were 40 μm and 50 μm
respectively (p = 0.009, and p < 0.001, respectively). For the 2°–4° region, the equivalent drusen heights that caused
significant shortening of segment length were 60 μm for IS (p = 0.017) and 80 μm for OS (p < 0.001)
We describe the design and performance of a recently implemented retinal imaging system for the human eye that combines adaptive optics (AO) with spectral domain optical coherence tomography (OCT) and scanning laser ophthalmoscopy (SLO). The AO-OCT-SLO system simultaneously acquires SLO frames and OCT B-scans at 60 Hz with an OCT volume acquisition scan rate of 0.24 Hz. The SLO images are used to correct for eye motion during the registration of OCT B-scans. Key optical design considerations are discussed including: minimizing system aberrations through the use of off-axis relay telescopes; choice of telescope magnification based on pupil plane requirements and restrictions; and the use of dichroic beam splitters to separate and re-combine OCT and SLO beams around the nonshared horizontal scanning mirrors. We include an analysis of closed-loop AO correction on a model eye and compare these findings with system performance in vivo. The 2D and 3D OCT scans included in this work demonstrate the ability of this system to laterally and axially resolve individual cone photoreceptors, while the corresponding SLO images show the en face mosaics at the photoreceptor layer showing rods and cones. Images from both healthy and diseased retina are presented.
The kinetics of resin composite polymerization plays an important, though not well understood, role it the
development of shrinkage stress and the resultant integrity of the final restoration. In this report we investigate the effect
of curing irradiance on the polymerization kinetics using a dynamic light scattering technique known as laser speckle
contrast analysis (LSCA). Thin layer samples are considered with focus given to the effect of sample thickness on the
rate results obtained with this method. We present results for the intensity fluctuation rate as a function of irradiance for
two statistical models of intensity decorrelation: Lorentzian and Gaussian. Results indicate that the rate of scatterer
motion varies approximately with the square root of irradiance, which agrees well with theory and previous results in the
literature. Our results suggest that dynamic light scattering techniques, and LSCA in particular, provide an effective,
non-contact means of assessing polymerization kinetics.
Polymer resin composites are a class of widely used restorative dental materials that undergo a complex polymerization
curing process that has been the subject of substantial research. This study uses speckle correlation methods based on
dynamic light scattering as a tool to monitor the rate and extent of dental composite polymerization during and after
photo-curing. Thin disc-shaped samples (<2mm) were constructed using composite consisting of 50:50
BisGMA/TEGDMA resin, quartz silica filler particles, and camphorquinone as photo-initiator. A 633 nm HeNe laser
beam was used to probe the top surface of the sample via a backscattered speckle pattern, while the bottom surface was
illuminated with a halogen curing lamp (peak wavelength=470nm) to initiate the polymerization reaction. The speckle
patterns were recorded with a CCD camera, and stored as a 'speckle cube' for post processing. Correlation values of the
intensity fluctuation were calculated on a pixel-by-pixel basis for pairs of subsequent speckle images and then ensemble
averaged. Results show a sharp decrease in correlation at the onset of curing, indicating a large amount of double bond
conversion and movement within the composite. Correlation values then quickly increase, eventually reaching a plateau
near unity, indicating cessation of molecular rearrangement. The kinetic behavior demonstrated by our correlation curves
are in good agreement with curing data found in the literature, and demonstrate the usefulness of this technique for
monitoring dental composite curing.
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