Many eye diseases, such as diabetic retinopathy (DR) and retinopathy of prematurity (ROP), can cause abnormalities at both central and peripheral regions of the fundus. Therefore, a wide field fundus imaging is desirable for screening, diagnosis, and treatment evaluation of eye diseases. The traditional fundus imaging device which uses trans-pupillary illumination has 30° to 60° field of view. In the trans-pupillary illumination, illumination path and observing path are typically separated by using different portions of the pupil to minimize the effect of reflectance artifact. Therefore, transpupillary illumination limits the field of view because only the central part can be used for imaging purpose. Transpalpebral illumination has been explored as an alternative approach to deliver light to the interior of the eye through the pars-plana, which enables capturing a wide portion of the fundus. Without the need of pharmacologic pupil dilation, a 150° visual angle fundus image was achieved. Previous studies implemented trans-palpebral illumination using a broadband LED. As it is well known that the transmission of long wavelength light is much higher than the short wavelength. Therefore, trans-palpebral illumination based fundus images are red oriented, with compromised image quality for visualizing retinal vasculatures. We have demonstrated the trans-palpebral illumination for the ultra-wide field fundus imaging. We report here the feasibility of using independent green and red illumination power controls to compensate for the difference of spectral efficiency. The color balanced trans-pars-planar illumination significantly increased dynamic range of the fundus camera.
This study is to validate the trans-pars-planar illumination for ultra-widefield multispectral imaging (MSI) of the retina and choroid. By freeing the available pupil for collecting imaging light only, the trans-pars-planar illumination enables a portable, nonmydriatic fundus camera, with 200o FOV in a single-shot image. The trans-pars-planar illumination, delivering illumination light from one side of the eye, naturally enables oblique illumination ophthalmoscopy to enhance the contrast of fundus imaging. Four wavelength LEDs, including 530 nm, 625 nm, 780 nm, and 970 nm, are illuminated for MSI of the retina and choroid.
Diabetic retinopathy (DR) and other eye diseases can affect artery and vein differently. Therefore, differential artery-vein analysis can improve disease detection and treatment assessment. This study aims to establish color fundus image analysis guided artery-vein differentiation in OCTA, and to verify that differential artery-vein analysis can improve the sensitivity of OCTA detection and classification of DR. Briefly, optical density ratio (ODR) analysis and blood vessel tracking were combined to identify artery-vein in color fundus images. The fundus artery-vein map was used to register arteries and veins in corresponding OCTA images. Based on the fundus image guided artery-vein differentiation, quantitative analysis of arteries and veins in control and NPDR OCTA images were performed. The sensitivities of traditional mean blood vessel caliber (m-BVC) and artery-vein ratio of BVC (AVR-BVC) were quantitatively compared for DR classification. One way, multi-label analysis of variance (ANOVA) with Bonferroni’s test and Student t-test was employed for evaluating classification performance. Images from 20 eyes of 18 control subjects and 48 eyes of 35 NPDR patients (18 mild, 16 moderate and 14 severe NPDR) were used for this study. Compared to m-BVC, AVR-BVC provided enhanced sensitivity in differentiating NPDR stages. AVR-BVC was able to differentiate among control and three different NPDR groups. AVR-BVC could also differentiate control from mild NPDR, promising a unique OCTA biomarker for detecting early onset of NPDR.
Differential artery-vein analysis is valuable for early detection of diabetic retinopathy (DR) and other eye diseases. As a new optical coherence tomography (OCT) imaging modality, emerging OCT angiography (OCTA) provides capillary level resolution for accurate examination of retinal vasculatures. However, differential artery-vein analysis in OCTA, particularly for macular region in which blood vessels are small, is challenging. In coordination with an automatic vessel tracking algorithm, we report here the feasibility of using near infrared OCT oximetry to guide artery-vein classification in OCTA of macular region.
In conventional fundus photography, illuminating light is delivered to the interior of the eye through the pupil. To avoid reflection from cornea and crystalline lens, peripheral area of the pupil is used for delivering illumination light and only the central part of the pupil can be used for collecting imaging light. Therefore, the optical design of conventional fundus cameras is sophisticated, the field of view is limited, and pupil dilation is required for evaluating the retinal periphery which is frequently affected by diabetic retinopathy (DR), retinopathy of premature (ROP), and other chorioretinal conditions. Trans-scleral illumination has been proposed as one alternative illumination method to achieve wide field fundus examination not requiring pharmacologic pupil dilation. However, clinical deployment of trans-scleral illumination failed due to the contact mode illumination and imaging, and complication of instrument operation. Here we report a nonmydriatic wide field fundus camera employing trans-pars-planar illumination which delivers illuminating light through the pars plana, an area outside of the pupil without contacting the eye. Trans-pars-planar illumination frees the entire pupil for imaging purpose only, and thus wide field fundus photography can be readily achieved with less pupil dilation. For proof-of-concept testing, using all off-the-shelf components a prototype instrument that can achieve 90° fundus view coverage in single-shot fundus images, without the need of pharmacologic pupil dilation was demonstrated.
It is known that wide-field fundus photography is essential for screening, diagnosis and treatment evaluation of eye diseases such as diabetic retinopathy (DR), age-related macular degeneration (AMD), retinopathy of premature (ROP), etc. However, the high equipment cost of existing devices is a limiting factor for clinical deployment of wide-field fundus photography, particularly in rural and underserved areas where both expensive instruments and skilled operators are not available. Low-cost smartphone fundus cameras promise convenient assessment of eye diseases at point-of-care environments, and may also enable affordable telemedicine screening to foster the access to medical cares in rural and underserved areas. However, practical application of existing smartphone fundus cameras is limited by the small field of view (FOV) in single-shot images. We have recently demonstrated the feasibility of trans-pars-planar illumination, i.e., delivering illuminating light through pars plana outside of the pupil. By freeing the whole pupil for image purpose only, the trans-pars-planar illumination provides one unique opportunity to develop snapshot, low-cost, but high-quality wide-field fundus camera. Using all off-the-shelf parts, a smartphone-based prototype fundus camera was constructed to achieve a 152-degree FOV in single-shot images, without the need for pharmacological pupil dilation. Moreover, we have also explored miniaturized indirect ophthalmoscopy to achieve wide-field fundus video photography. A totally wireless smartphone fundus camera was constructed, with a whole weight of 255 g. This device allowed both snapshot fundus photography and continuous video recording.
It is known that retinopathies may affect arteries and veins differently. Therefore, reliable differentiation of arteries and veins is essential for computer-aided analysis of fundus images. The purpose of this study is to validate one automated method for robust classification of arteries and veins (A-V) in digital fundus images. We combine optical density ratio (ODR) analysis and blood vessel tracking algorithm to classify arteries and veins. A matched filtering method is used to enhance retinal blood vessels. Bottom hat filtering and global thresholding are used to segment the vessel and skeleton individual blood vessels. The vessel tracking algorithm is used to locate the optic disk and to identify source nodes of blood vessels in optic disk area. Each node can be identified as vein or artery using ODR information. Using the source nodes as starting point, the whole vessel trace is then tracked and classified as vein or artery using vessel curvature and angle information. 50 color fundus images from diabetic retinopathy patients were used to test the algorithm. Sensitivity, specificity, and accuracy metrics were measured to assess the validity of the proposed classification method compared to ground truths created by two independent observers. The algorithm demonstrated 97.52% accuracy in identifying blood vessels as vein or artery. A quantitative analysis upon A-V classification showed that average A-V ratio of width for NPDR subjects with hypertension decreased significantly (43.13%).
In conventional fundus imaging devices, transpupillary illumination is used for illuminating the inside of the eye. In this method, the illumination light is directed into the posterior segment of the eye through the cornea and passes the pupillary area. As a result of sharing the pupillary area for the illumination beam and observation path, pupil dilation is typically necessary for wide-angle fundus examination, and the field of view is inherently limited. An alternative approach is to deliver light from the sclera. It is possible to image a wider retinal area with transcleral-illumination. However, the requirement of physical contact between the illumination probe and the sclera is a drawback of this method. We report here trans-palpebral illumination as a new method to deliver the light through the upper eyelid (palpebra). For this study, we used a 1.5 mm diameter fiber with a warm white LED light source. To illuminate the inside of the eye, the fiber illuminator was placed at the location corresponding to the pars plana region. A custom designed optical system was attached to a digital camera for retinal imaging. The optical system contained a 90 diopter ophthalmic lens and a 25 diopter relay lens. The ophthalmic lens collected light coming from the posterior of the eye and formed an aerial image between the ophthalmic and relay lenses. The aerial image was captured by the camera through the relay lens. An adequate illumination level was obtained to capture wide angle fundus images within ocular safety limits, defined by the ISO 15004-2: 2007 standard. This novel trans-palpebral illumination approach enables wide-angle fundus photography without eyeball contact and pupil dilation.
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