Past, Present, and Future Concepts of the Choroidal Scleral Interface Morphology on Optical Coherence Tomography.

The choroid is the most vascular tissue in the eye and it has been implicated in the pathophysiology of a variety of ocular diseases. A new era of research in the choroid began with the improved ability to visualize this layer and its inner and outer boundaries using spectral domain optical coherence tomography (OCT) with enhanced depth imaging and swept source OCT. The accuracy and precision of qualitative and quan-titative assessments of the choroidal layer support the potential use of OCT-derived choroidal parameters for diagnosis, monitoring of disease progression, planning surgical access, and evaluating treatment response. Although there is increasing interest in measuring choroidal thickness, there is currently no consensus nomenclature to classify choroidal layers and boundaries. Furthermore, the definition and description of the choroidal scleral interface is inconsistent in the literature, contributing to interstudy variation in choroidal thickness measurements. The purpose of this review is to provide an overview of the literature on the definition of choroidal layers and choroidal scleral boundary, review the discrepan-cies, and harmonize the terminology so that a consensus nomenclature can be proposed.

FUNDUS AUTOFLUORESCENCE IN RUBELLA RETINOPATHY: Correlation With Photoreceptor Structure and Function.

PURPOSE: To illustrate altered fundus autofluorescence in rubella retinopathy and to investigate their relationships with photoreceptor structure and function using multimodal imaging. METHODS: The authors report four cases of rubella retinopathy aged 8, 33, 42, and 50 years. All patients had dilated clinical fundus examination; wide-field color photography; blue, green, and near-infrared autofluorescence imaging and spectral domain optical coherence tomography. Two patients also underwent microperimetry and adaptive optics imaging. En face optical coherence tomography, cone mosaic, and microperimetry were coregistered with autofluorescence images. The authors explored the structure-function correlation. RESULTS: All four patients had a "salt-and-pepper" appearance on dilated fundus examination and wide-field color photography. There were variable-sized patches of hypoautofluorescence on both blue and near-infrared excitation in all four patients. Wave-guiding cones were visible and retinal sensitivity was intact over these regions. There was no correlation between hypoautofluorescence and regions of attenuated ellipsoid and interdigitation zones. Hyperautofluorescent lesions were also noted and some of these were pseudo-vitelliform lesions. CONCLUSION: Patchy hypoautofluorescence on near-infrared excitation can be a feature of rubella retinopathy. This may be due to abnormal melanin production or loss of melanin within retinal pigment epithelium cells harboring persistent rubella virus infection. Preservation of the ellipsoid zone, wave-guiding cones, and retinal sensitivity within hypoautofluorescent lesions suggest that these retinal pigment epithelium changes have only mild impact on photoreceptor cell function.

Quantification of sun-related changes in the eye in conjunctival ultraviolet autofluorescence images.

Quantification of sun-related changes in conjunctival ultraviolet autofluorescence (CUVAF) images is a subjective and tedious task, in which reproducibility of results is difficult. Thus, we have developed a semiautomatic method in MATLAB(®) to analyze CUVAF images retrospectively. The algorithm was validated on 200 images from 50 randomly selected participants from the Western Australian Pregnancy Cohort (Raine) study 20-year follow-up assessment, in which CUVAF area measurements were available from previous manual analysis. Algorithm performance was compared to manual measurements and yielded better than 95% correspondence in both intra- and interobserver agreement. Furthermore, the semiautomatic method significantly reduced analysis time by 50%.

Classification of image artefacts in optical coherence tomography angiography of the choroid in macular diseases.

BACKGROUND: To evaluate and classify image artefacts in optical coherence tomography (OCT) angiography (OCTA) of the choroid in a group of patients with macular diseases. DESIGN: Retrospective observational study. PARTICIPANTS: Five patients with age-related macular degeneration, three with central serous retinopathy, one with polypoidal choroidal vasculopathy and one with multiple evanescent white dot syndrome. METHODS: OCTA and OCT reflectivity (OCTR) maps were reviewed along with their fluorescein angiography and indocyanine green angiography. Sixty OCTA images (20 outer retina, 20 Sattler and 20 Haller layers) were graded for image artefacts by two examiners independently. MAIN OUTCOME MEASURES: OCTA artefacts and their correlation with OCTR maps, angiography and OCT B-scans. RESULTS: Artefacts (frequency) were classified into (i) motion (70-100%), (ii) fringe washout (100%), (iii) decorrelation projection (0-20%), (iv) masking and unmasking (50-65%) and (v) stromal decorrelation signal (100%). Motion artefact in OCTA is characterized by horizontal dark lines or bands not apparent on OCTR map. Fringe washout creates signal void within choroidal vessels because of fast blood flow. Decorrelation projection from retinal vasculature and choroidal new vessels above the Bruch's membrane are seen within the choroidal OCTA image. Masking and unmasking artefacts occur in regions of pigment epithelial detachment and atrophy. Decorrelation signals can also be seen in the choroidal stroma. CONCLUSIONS: Our classification system of artefact in choroidal OCTA establishes a common terminology for clinical interpretation. This is important in enhancing our understanding of the principles of OCTA acquisition, and it also serves as a bench mark for reading centres.

Semi-automated identification of cones in the human retina using circle Hough transform.

A large number of human retinal diseases are characterized by a progressive loss of cones, the photoreceptors critical for visual acuity and color perception. Adaptive Optics (AO) imaging presents a potential method to study these cells in vivo. However, AO imaging in ophthalmology is a relatively new phenomenon and quantitative analysis of these images remains difficult and tedious using manual methods. This paper illustrates a novel semi-automated quantitative technique enabling registration of AO images to macular landmarks, cone counting and its radius quantification at specified distances from the foveal center. The new cone counting approach employs the circle Hough transform (cHT) and is compared to automated counting methods, as well as arbitrated manual cone identification. We explore the impact of varying the circle detection parameter on the validity of cHT cone counting and discuss the potential role of using this algorithm in detecting both cones and rods separately.

Differentiation of morphotic elements in human blood using optical coherence tomography and a microfluidic setup.

We demonstrate a novel optical method for the detection and differentiation between erythrocytes and leukocytes that uses amplitude and phase information provided by optical coherence tomography (OCT). Biological cells can introduce significant phase modulation with substantial scattering anisotropy and dominant forward-scattered light. Such physical properties may favor the use of a trans-illumination imaging technique. However, an epi-illumination mode may be more practical and robust in many applications. This study describes a new way of measuring the phase modulation introduced by flowing microobjects. The novel part of this invention is that it uses the backscattered signal from the substrate located below the flowing/moving objects. The identification of cells is based on phase-sensitive OCT signals. To differentiate single cells, a custom-designed microfluidic device with a highly scattering substrate is introduced. The microchannels are molded in polydimethylsiloxane (PDMS) mixed with titanium dioxide (TiO2) to ensure high scattering properties. The statistical parameters of the measured signal depend on the cells' features, such as their size, shape, and internal structure.

Posterior Cortical Atrophy Presenting with Superior Arcuate Field Defect.

An 80-year-old female with reading difficulty presented with progressive arcuate field defect despite low intraocular pressure. Over a 5-year period, the field defect evolved into an incongruous homonymous hemianopia and the repeated neuroimaging revealed progressive posterior cortical atrophy. Further neuropsychiatric assessment demonstrated symptoms and signs consistent with Benson's syndrome.

OCT angiography by absolute intensity difference applied to normal and diseased human retinas.

We compare four optical coherence tomography techniques for noninvasive visualization of microcapillary network in the human retina and murine cortex. We perform phantom studies to investigate contrast-to-noise ratio for angiographic images obtained with each of the algorithm. We show that the computationally simplest absolute intensity difference angiographic OCT algorithm that bases only on two cross-sectional intensity images may be successfully used in clinical study of healthy eyes and eyes with diabetic maculopathy and branch retinal vein occlusion.

Spectral OCT with speckle contrast reduction for evaluation of the healing process after PRK and transepithelial PRK.

We evaluate Spectral OCT (SOCT) with a speckle contrast reduction technique using resonant scanner for assessment of corneal surface changes after excimer laser photorefractive keratectomy (PRK) and we compare healing process between conventional PRK and transepithelial PRK. The measurements were performed before and after the surgery. Obtained results show that SOCT with a resonant scanner speckle contrast reduction is capable of providing information regarding the healing process after PRK. The main difference between the healing processes of PRK and TransPRK, assessed by SOCT, was the time to cover the stroma with epithelium, which was shorter in the TransPRK group.

Assessment of the flow velocity of blood cells in a microfluidic device using joint spectral and time domain optical coherence tomography.

Although Doppler optical coherence tomography techniques have enabled the imaging of blood flow in mid-sized vessels in biological tissues, the generation of velocity maps of capillary networks remains a challenge. To better understand the origin and information content of the Doppler signal from small vessels and limitations of such measurements, we used joint spectral and time domain optical coherence tomography to monitor the flow in a model, semitransparent microchannel device. The results obtained for Intralipid, whole blood, as well as separated red blood cells indicate that the technique is suitable to record velocity profiles in vitro, in a range of microchannel configurations.

Multi-parametric imaging of murine brain using spectral and time domain optical coherence tomography.

Examination of brain functions in small animal models may help improve the diagnosis and treatment of neurological conditions. Transcranial imaging of small rodents' brains poses a major challenge for optical microscopy. Another challenge is to reduce the measurement time. We describe methods and algorithms for three-dimensional assessment of blood flow in the brains of small animals, through the intact skull, using spectral and time domain optical coherence tomography. By introducing a resonant scanner to the optical setup of the optical coherence tomography (OCT) system, we have developed and applied a high-speed spectral OCT technique that allows us to vary the imaging range of flow and to shorten measurement time. Multi-parameter signal analysis enables us to obtain both qualitative and quantitative information about flow velocity from the same set of data.

Four-dimensional structural and Doppler optical coherence tomography imaging on graphics processing units.

The authors present the application of graphics processing unit (GPU) programming for real-time three-dimensional (3-D) Fourier domain optical coherence tomography (FdOCT) imaging with implementation of flow visualization algorithms. One of the limitations of FdOCT is data processing time, which is generally longer than data acquisition time. Utilizing additional algorithms, such as Doppler analysis, further increases computation time. The general purpose computing on GPU (GPGPU) has been used successfully for structural OCT imaging, but real-time 3-D imaging of flows has so far not been presented. We have developed software for structural and Doppler OCT processing capable of visualization of two-dimensional (2-D) data (2000 A-scans, 2048 pixels per spectrum) with an image refresh rate higher than 120 Hz. The 3-D imaging of 100×100 A-scans data is performed at a rate of about 9 volumes per second. We describe the software architecture, organization of threads, and optimization. Screen shots recorded during real-time imaging of a flow phantom and the human eye are presented.

Drusen with accompanying fluid underneath the sensory retina.

PURPOSE: To investigate whether confluent drusen may be accompanied by fluid accumulation underneath the sensory retina and to determine if the detection of subretinal fluid on spectral-domain optical coherence tomography (OCT) in patients with coalescent drusen is indicative of choroidal neovascularization (CNV). DESIGN: Prospective, noncomparative case series. PARTICIPANTS: Seventy-four eyes of 57 patients with large, confluent drusen. METHODS: The retinal structure of patients with coalescent drusen was studied by spectral-domain OCT. Optical coherence tomography reflectivity and outer retina topography maps were created and compared with fluorescein angiography (FA) and indocyanine green angiography (ICGA) images as well as with microperimetry. MAIN OUTCOME MEASURES: Optical coherence tomography-derived retinal morphologic features. RESULTS: What appears to be fluid beneath the sensory retina was found on spectral-domain OCT in 8 eyes of 7 patients. The outer retina topography maps demonstrated that fluid accumulates only in the concavity between clustering soft drusen, not on their outward slopes. The maps also revealed a reduced distance between the retinal pigment epithelium (RPE) and the photoreceptor inner/outer segment (IS/OS) junction over large drusen and tiny elevations of the IS/OS junction around drusen of all sizes. Microperimetry showed decreased retinal light sensitivity at the site of diminished distance between the RPE and the IS/OS junction. Seven eyes of 6 patients who were followed up were found to have no retinal changes other than confluent drusen along with subretinal fluid during the entire observational period (12-27 months). There was no evidence of CNV on FA or ICGA in any of the patients. CONCLUSIONS: Large, confluent drusen may be accompanied by subretinal spaces that appear to be filled with fluid. Specific distribution of the fluid limited to the depression between adjacent drusen may indicate that the cluster of coalescent drusen produces mechanical strain to the outer retinal layers that locally pulls the sensory retina away from its normal position. Consequently, the appearance of fluid within subretinal compartment between coalescent drusen in OCT cross-sectional images may not be a reliable marker for the presence of CNV.

Comparison of reflectivity maps and outer retinal topography in retinal disease by 3-D Fourier domain optical coherence tomography.

We demonstrate and compare two image processing methods for visualization and analysis of three-dimensional optical coherence tomography (OCT) data acquired in eyes with different retinal pathologies. A method of retinal layer segmentation based on a multiple intensity thresholding algorithm was implemented in order to generate simultaneously outer retinal topography maps and reflectivity maps. We compare the applicability of the two methods to the diagnosis of retinal diseases and their progression. The data presented in this contribution were acquired with a high speed (25,000 A-scans/s), high resolution (4.5 microm) spectral OCT prototype instrument operating in the ophthalmology clinic.