Tracking features in retinal images of adaptive optics confocal scanning laser ophthalmoscope using KLT-SIFT algorithm.
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ABSTRACT:
SUBMITTER: Li H
PROVIDER: S-EPMC3005164 | biostudies-other | 2010
REPOSITORIES: biostudies-other
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Project description:To develop and test the application of an adaptive optics scanning laser ophthalmoscope (AOSLO) with eye tracking for high-resolution microperimetric testing.An AOSLO was used to conduct simultaneous high-resolution retinal imaging and visual function testing in six normal subjects. Visual sensitivity was measured at test locations between the fovea and 5.0° eccentricity via an increment threshold approach using a 40-trial, yes-no adaptive Bayesian staircase procedure (QUEST). A high-speed eye tracking algorithm enabled real-time video stabilization and the delivery of diffraction-limited Goldmann I-sized stimuli (diameter = 6.5 arc min = ?32 ?m; ? = 680 nm) to targeted retinal loci for 200 ms. Test locations were selected either manually by the examiner or automatically using Fourier-based image registration. Cone spacing was assessed at each test location and sensitivity was plotted against retinal eccentricity. Finally, a 4.2 arc min stimulus was used to probe the angioscotoma associated with a blood vessel located at 2.5° eccentricity.Visual sensitivity decreases with eccentricity at a rate of -1.32 dB/deg (R = 0.60). The vertical and horizontal errors of the targeted stimulus delivery algorithm averaged 0.81 and 0.89 arc min (?4 ?m), respectively. Based on a predetermined exclusion criterion, the stimulus was successfully delivered to its targeted location in 90.1% of all trials. Automated recovery of test locations afforded the repeat testing of the same set of cones over a period of 3 months. Thresholds measured over a parafoveal blood vessel were 1.96 times higher (p < 0.05; one-tailed t-test) than those measured in directly adjacent retina.AOSLO-based microperimetry has the potential to test visual sensitivity with fine retinotopic precision. Automated recovery of previously tested locations allows these measures to be tracked longitudinally. This approach can be implemented by researchers interested in establishing the functional correlates of photoreceptor mosaic structure in patients with retinal disease.
| S-EPMC3348404 | biostudies-literature
Project description:PurposeAdaptive optics scanning laser ophthalmoscope (AOSLO) capillary perfusion images can possess large variations in contrast, intensity, and background signal, thereby limiting the use of global or adaptive thresholding techniques for automatic segmentation. We sought to develop an automated approach to segment perfused capillaries in AOSLO images.Methods12,979 image patches were extracted from manually segmented AOSLO montages from 14 eyes and used to train a convolutional neural network (CNN) that classified pixels as capillaries, large vessels, background, or image canvas. 1764 patches were extracted from AOSLO montages of four separate subjects, and were segmented manually by two raters (ground truth) and automatically by the CNN, an Otsu's approach, and a Frangi approach. A modified Dice coefficient was created to account for slight spatial differences between the same manually and CNN-segmented capillaries.ResultsCNN capillary segmentation had an accuracy (0.94), a Dice coefficient (0.67), and a modified Dice coefficient (0.90) that were significantly higher than other automated approaches (P < 0.05). There were no significant differences in capillary density and mean segment length between manual ground-truth and CNN segmentations (P > 0.05).ConclusionsClose agreement between the CNN and manual segmentations enables robust and objective quantification of perfused capillary metrics. The developed CNN is time and computationally efficient, and distinguishes capillaries from areas containing diffuse background signal and larger underlying vessels.Translational relevanceThis automatic segmentation algorithm greatly increases the efficiency of quantifying AOSLO capillary perfusion images.
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Project description:We demonstrate a system that combines a tracking scanning laser ophthalmoscope (TSLO) and an adaptive optics scanning laser ophthalmoscope (AOSLO) system resulting in both optical (hardware) and digital (software) eye-tracking capabilities. The hybrid system employs the TSLO for active eye-tracking at a rate up to 960 Hz for real-time stabilization of the AOSLO system. AOSLO videos with active eye-tracking signals showed, at most, an amplitude of motion of 0.20 arcminutes for horizontal motion and 0.14 arcminutes for vertical motion. Subsequent real-time digital stabilization limited residual motion to an average of only 0.06 arcminutes (a 95% reduction). By correcting for high amplitude, low frequency drifts of the eye, the active TSLO eye-tracking system enabled the AOSLO system to capture high-resolution retinal images over a larger range of motion than previously possible with just the AOSLO imaging system alone.
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Project description:We describe an ultrahigh-resolution (UHR) retinal imaging system that combines adaptive optics Fourier-domain optical coherence tomography (AO-OCT) with an adaptive optics scanning laser ophthalmoscope (AO-SLO) to allow simultaneous data acquisition by the two modalities. The AO-SLO subsystem was integrated into the previously described AO-UHR OCT instrument with minimal changes to the latter. This was done in order to ensure optimal performance and image quality of the AO- UHR OCT. In this design both imaging modalities share most of the optical components including a common AO-subsystem and vertical scanner. One of the benefits of combining Fd-OCT with SLO includes automatic co-registration between two acquisition channels for direct comparison between retinal structures imaged by both modalities (e.g., photoreceptor mosaics or microvasculature maps). Because of differences in the detection scheme of the two systems, this dual imaging modality instrument can provide insight into retinal morphology and potentially function, that could not be accessed easily by a single system. In this paper we describe details of the components and parameters of the combined instrument, including incorporation of a novel membrane magnetic deformable mirror with increased stroke and actuator count used as a single wavefront corrector. We also discuss laser safety calculations for this multimodal system. Finally, retinal images acquired in vivo with this system are presented.
| S-EPMC3114233 | biostudies-other
Project description:We present an adaptive optics parallel near-confocal scanning ophthalmoscope (AOPCSO) using a digital micromirror device (DMD). The imaging light is modulated to be a line of point sources by the DMD, illuminating the retina simultaneously. By using a high-speed line camera to acquire the image and using adaptive optics to compensate the ocular wave aberration, the AOPCSO can image the living human eye with cellular level resolution at the frame rate of 100 Hz. AOPCSO has been demonstrated with improved spatial resolution in imaging of the living human retina compared with adaptive optics line scan ophthalmoscopy.
| S-EPMC5218998 | biostudies-other
Project description:Retinal vascular diseases are a leading cause of blindness and visual disability. The advent of adaptive optics retinal imaging has enabled us to image the retinal vascular at cellular resolutions, but imaging of the vasculature can be difficult due to the complex nature of the images, including features of many other retinal structures, such as the nerve fiber layer, glial and other cells. In this paper we show that varying the size and centration of the confocal aperture of an adaptive optics scanning laser ophthalmoscope (AOSLO) can increase sensitivity to multiply scattered light, especially light forward scattered from the vasculature and erythrocytes. The resulting technique was tested by imaging regions with different retinal tissue reflectivities as well as within the optic nerve head.
| S-EPMC3470005 | biostudies-other
Project description:We developed a clinical ophthalmic prototype by combining bimorph deformable mirror (DM)-based adaptive optics (AO) with a confocal scanning laser ophthalmoscope. A low-cost bimorph DM with a large stroke of 50???m and an aperture of 20 mm was utilized to realize a strategy for successive AO control of aberration correction, which permitted open-loop compensation for low-order aberrations and closed-loop correction of high-order aberrations to acceptable root mean square errors of <0.08???m in all subjects. Spherical mirrors were folded in a nonplanar configuration to minimize off-axis aberrations and provide a compact, cost-effective design, which achieved a diffraction-limited performance capable of imaging individual photoreceptor cells and blood vessels not only in healthy subjects but also in patients suffering from retinitis pigmentosa. The adaptive optics scanning laser ophthalmoscope (AOSLO) images of the diseased retina had much higher resolutions than those captured by the commercial AO fundus camera, and loss of the photoreceptor mosaic could be distinguished more accurately due to the improvement in resolution. The compact design and easy handling of the bimorph DM-based AO control may facilitate the translation of AOSLO into clinical settings, and this prototype development will continue with future device refinement and extensive clinical testing.
| S-EPMC6830288 | biostudies-literature
Project description:PurposeTo compare the use of optical coherence tomography angiography (OCTA) and adaptive optics scanning light ophthalmoscope fluorescein angiography (AOSLO FA) for characterizing the foveal microvasculature in healthy and vasculopathic eyes.MethodsFour healthy controls and 11 vasculopathic patients (4 diabetic retinopathy, 4 retinal vein occlusion, and 3 sickle cell retinopathy) were imaged with OCTA and AOSLO FA. Foveal perfusion maps were semiautomatically skeletonized for quantitative analysis, which included foveal avascular zone (FAZ) metrics (area, perimeter, acircularity index) and vessel density in three concentric annular regions of interest. On each set of OCTA and AOSLO FA images, matching vessel segments were used for lumen diameter measurement. Qualitative image comparisons were performed by visual identification of microaneurysms, vessel loops, leakage, and vessel segments.ResultsAdaptive optics scanning light ophthalmoscope FA and OCTA showed no statistically significant differences in FAZ perimeter, acircularity index, and vessel densities. Foveal avascular zone area, however, showed a small but statistically significant difference of 1.8% (P = 0.004). Lumen diameter was significantly larger on OCTA (mean difference 5.7 μm, P < 0.001). Microaneurysms, fine structure of vessel loops, leakage, and some vessel segments were visible on AOSLO FA but not OCTA, while blood vessels obscured by leakage were visible only on OCTA.ConclusionsOptical coherence tomography angiography is comparable to AOSLO FA at imaging the foveal microvasculature except for differences in FAZ area, lumen diameter, and some qualitative features. These results, together with its ease of use, short acquisition time, and avoidance of potentially phototoxic blue light, support OCTA as a tool for monitoring ocular pathology and detecting early disease.
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Project description:A limitation of scanning laser ophthalmoscopy (SLO) is that eye movements during the capture of each frame distort the retinal image. Various sophisticated strategies have been devised to ensure that each acquired frame can be mapped quickly and accurately onto a chosen reference frame, but such methods are blind to distortions in the reference frame itself. Here we explore a method to address this limitation in software, and demonstrate its accuracy. We used high-speed (200 fps), high-resolution (~1 μm), flood-based imaging of the human retina with adaptive optics to obtain "ground truth" information on the retinal image and motion of the eye. This information was used to simulate SLO video sequences at 20 fps, allowing us to compare various methods for eye-motion recovery and subsequent minimization of intra-frame distortion. We show that a) a single frame can be near-perfectly recovered with perfect knowledge of intra-frame eye motion; b) eye motion at a given time point within a frame can be accurately recovered by tracking the same strip of tissue across many frames, due to the stochastic symmetry of fixational eye movements. This approach is similar to, and easily adapted from, previously suggested strip-registration approaches; c) quality of frame recovery decreases with amplitude of eye movements, however, the proposed method is affected less by this than other state-of-the-art methods and so offers even greater advantages when fixation is poor. The new method could easily be integrated into existing image processing software, and we provide an example implementation written in Matlab.
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Project description:Fundus albipunctatus (FA) is a form of congenital stationary night blindness characterized by yellow-white spots, which were classically described as subretinal. Although night blindness and delayed dark adaptation are hallmarks of this condition, recent studies have described a macular phenotype, particularly among older patients. Using a fluorescence adaptive optics scanning laser ophthalmoscope (FAOSLO), this study provides in vivo morphologic data at the cellular level in FA.To study the cone photoreceptors and the albipunctate spots in FA at single-cell resolution.A woman in her 30s with FA underwent a complete ophthalmic examination, including conventional imaging tests, at the University of Rochester. A FAOSLO was used to obtain infrared reflectance images of the cone mosaic at the central fovea and along the superior and temporal meridians to 10° eccentricity. Cone density was measured at the foveal center, and cone spacing was calculated in sampling windows eccentrically. In the area of the albipunctate spots, autofluorescence FAOSLO images (excitation, 561 nm; emission, 624 ? 40 nm) were simultaneously obtained.Structural appearance of cones, cone density and spacing, and reflectance and autofluorescence of albipunctate spots.Cone density was reduced to 70% of the lower limit of the normal range at the foveal center (78.7 × 10(3) cones/mm(2); mean [SD] reference range, 199 [87] × 10(3) cones/mm(2)), and cone spacing was increased eccentrically to 10° (sign test, P =?.045). Individual cone central core reflectances appeared dim, suggesting loss of photoreceptor outer segments. The albipunctate spots were hypoautofluorescent. No photoreceptors or retinal pigment epithelium cells were identified at the locations of the albipunctate spots.Although the predominant clinical symptom of night blindness and the electroretinography results suggest a primary rod dysfunction, examination with a FAOSLO demonstrates that cone density is also reduced. This finding may represent an early sign of progression to macular phenotype in FA. The hypoautofluorescence suggests that the albipunctate spots do not represent lipofuscin.
| S-EPMC4162840 | biostudies-literature