Mojtaba Rahimi

Effective evaluation, documentation, and management of eye diseases require robust visualization of the peripheral posterior segment. However, currently available portable fundus cameras offer restricted fields of view (FOV). Conversely, benchtop fundus cameras and scanning laser ophthalmoscopes (SLOs) offer a wide FOV but lack portability, incur high capital costs, and require strict patient cooperation, limiting their utility in emergency care, intraoperative monitoring, and remote screening. To address these limitations, we present a handheld, nonmydriatic, multispectral fundus camera capable of capturing a 200° eye angle (143° visual angle) single-shot FOV using trans-pars-planar illumination. By integrating two visible and two near-infrared (NIR) wavelengths, we can selectively image biomarkers and structures situated across the full depth of the posterior segment. Furthermore, the extreme periphery of the posterior segment could be reached with gentle rotational scanning. Supported by an integrated embedded computing and display module, the device operates completely standalone and is immediately deployable in clinics. This portable imager promises an affordable solution for dilation-free, high-quality pan-retinal assessment, with the potential to expand access to advanced posterior eye diagnostics in emergency departments, operating rooms, and teleophthalmology settings.

This study verifies anisotropic vessel pulsatility in human retinas. Doppler optical coherence tomography (OCT) was utilized for dynamic monitoring of peripapillary vessel lumen dynamics. Quantitative analysis consistently revealed larger axial compared to lateral lumen changes, with an axial-to-lateral pulsation change ratio of 1.26 ± 0.08. These findings highlight the anisotropic biomechanical properties of retinal tissues, which contribute to direction-dependent vascular dynamics. Quantitative assessment of anisotropic vascular biomechanics offers promising insights for improving the detection of vascular alterations associated with ocular conditions.

Early detection of retinal diseases and effective monitoring of treatment responses rely on quantitative analysis of key biomarkers, including microvascular changes in the retina. Various diseases, such as diabetic retinopathy (DR), strokes (cerebrovascular accidents), hypertensive retinopathy, and different vascular disorders, can cause alterations in retinal vasculature.^1,2 DR, in particular, primarily affects microvasculature, leading to capillary level changes detectable with advanced imaging techniques. Optical coherence tomography angiography (OCTA) provides a noninvasive way to visualize retinal capillary networks with micrometer-level resolution, enabling the precise assessment of retinal neurovascular changes.³ A growing body of research^{4 – 12} has focused on the quantitative analysis of OCTA images to assess microvascular alterations and objectively classify retinal diseases. These studies have highlighted the effectiveness of using OCTA-based metrics to detect subtle changes in the retinal microvasculature, thus providing a refined approach to early diagnosis and disease stratification. Efforts to distinguish arteries and veins in OCTA imaging have refined retinal disease classification, as these vessels show distinct pathological changes.^13,14 Advanced machine learning techniques have improved their automated segmentation, enhancing diagnostic precision and providing insights into specific vascular alterations in DR.^{15 – 21}

The choroid, a critical vascular layer beneath the retina, is essential for maintaining retinal function and monitoring chorioretinal disorders. Existing imaging methods, such as indocyanine green angiography (ICGA) and optical coherence tomography (OCT), face significant limitations, including contrast agent requirements, restricted field of view (FOV), and high costs, limiting accessibility. To address these challenges, we developed a nonmydriatic, contrast agent-free fundus camera utilizing transcranial near-infrared (NIR) illumination. This system achieves a wide snapshot FOV of up to 185° eye-angle (130° visual-angle) without pharmacological pupillary dilation or contrast agents. By montaging two HDR images, the effective FOV can exceed 220° eye-angle (160° visual angle). Employing high dynamic range (HDR) imaging, the device ensures uniform contrast and enhanced choroidal visualization by correcting illumination inhomogeneity. The system demonstrated imaging performance comparable to ICGA when tested on healthy participants and patients with choroidal conditions, offering improved accessibility and affordability. This innovation holds promise for advancing the screening, diagnosis, and management of choroidal disorders, particularly in underserved settings.

Widefield fundus photography is critical for the detection, documentation, and management of pediatric eye diseases. Existing clinical pediatric fundus cameras offer a limited field of view (FOV) and suboptimal image contrast, hindering comprehensive peripheral retina examination. Additionally, the high cost and lack of portability of commercial devices restrict their use in resource-limited settings. We introduce a cost-effective smartphone-based pediatric camera (PedCam) that provides a 180° eye angle (126° visual angle) snapshot FOV. Utilizing trans-pars planar illumination, the device enables nonmydriatic imaging by allocating the pupil exclusively for imaging, eliminating the need for pharmacological pupillary dilation. By adjusting the optical axis of the PedCam relative to the ocular axis, the effective FOV can be expanded up to 240° eye angle (180° visual angle), enabling complete retinal evaluation. This innovative smartphone PedCam represents a significant advancement in affordable telemedicine for the screening, monitoring, and management of retinopathy of prematurity and other pediatric eye conditions.

Retinopathy of prematurity (ROP) occurs in premature infants due to underdeveloped retinal vasculature at birth,¹ causing abnormal blood vessel growth at the boundary of partially vascularized and avascular retinal areas.^2,3 ROP is the leading preventable cause of childhood blindness worldwide.^4,5 The severity of ROP is classified into five stages, corresponding to mild to severe stages.⁶ Appropriate detection and accurate ROP diagnosis in premature infants is crucial to prevent irreversible vision loss and associated visual developmental complications such as astigmatism, myopia, glaucoma, cataracts, anisometropia, amblyopia, strabismus, and retinal detachment.^7,8

This study investigates the impact of differential artery-vein (AV) analysis in optical coherence tomography angiography (OCTA) on machine learning classification of diabetic retinopathy (DR). Leveraging deep learning for arterial-venous area (AVA) segmentation, six quantitative features, including perfusion intensity density (PID), blood vessel density (BVD), vessel area flux (VAF), blood vessel caliber (BVC), blood vessel tortuosity (BVT), and vessel perimeter index (VPI) features, were derived from OCTA images before and after AV differentiation. A support vector machine (SVM) classifier was utilized to assess both binary and multiclass classifications of control, diabetic patients without DR (NoDR), mild DR, moderate DR, and severe DR groups. Initially, one-region features, i.e., quantitative features extracted from the entire OCTA, were evaluated for DR classification. Differential AV analysis improved classification accuracies from 78.86% to 87.63% and from 79.62% to 85.66% for binary and multiclass classifications, respectively. Additionally, three-region features derived from the entire image, parafovea, and perifovea, were incorporated for DR classification. Differential AV analysis further enhanced classification accuracies from 84.43% to 93.33% and from 83.40% to 89.25% for binary and multiclass classifications, respectively. These findings highlight the potential of differential AV analysis in augmenting disease diagnosis and treatment assessment using OCTA.

Ultrasound A-scan is an important tool for quantitative assessment of ocular lesions. However, its usability is limited by the difficulty of accurately localizing the ultrasound probe to a lesion of interest. In this study, a transparent LiNbO₃ single crystal ultrasound transducer was fabricated, and integrated with a widefield fundus camera to guide the ultrasound local position. The electrical impedance, phase spectrum, pulse-echo performance, and optical transmission spectrum of the ultrasound transducer were validated. The novel fundus camera-guided ultrasound probe was tested for in vivo measurement of rat eyes. Anterior and posterior segments of the rat eye could be unambiguously differentiated with the fundus photography-guided ultrasound measurement. A model eye was also used to verify the imaging performance of the prototype device in the human eye. The prototype shows the potential of being used in the clinic to accurately measure the thickness and echogenicity of ocular lesions in vivo.

Ultrasound A-scan is an important tool for quantitative assessment of ocular lesions. However, its usability is limited by difficulty to accurately localize the ultrasound probe to a lesion of interest. In this study, a transparent LiNbO3 single crystal ultrasound transducer was fabricated, and integrated with a widefield fundus camera to guide the ultrasound local position. The novel fundus camera guided ultrasound probe was validated for in vivo measurement of rat eyes. Anterior and posterior segments of the rat eye could be unambiguously differentiated with the fundus photography guided ultrasound measurement. A model eye was also used to verify the clinical potential of the prototype device.

The purpose of this study is to demonstrate the feasibility of using polarization maintaining photons for enhanced contrast imaging of the retina. Orthogonal-polarization control has been frequently used in conventional fundus imaging systems to minimize reflection artifacts. However, the orthogonal-polarization configuration also rejects the directly reflected photons, which preserve the polarization condition of incident light, from the superficial layer of the fundus, i.e., the retina, and thus reduce the contrast of retinal imaging. We report here a portable fundus camera which can simultaneously perform orthogonal-polarization control to reject back-reflected light from the ophthalmic lens and parallel-polarization control to preserve the backscattered light from the retina which partially maintains the polarization state of the incoming light. This portable device utilizes miniaturized indirect ophthalmoscopy illumination to achieve non-mydriatic imaging, with a snapshot field of view of 101° eye-angle (67° visual-angle). Comparative analysis of retinal images acquired with a traditional orthogonal-polarization fundus camera from both normal and diseased eyes was conducted to validate the usefulness of the proposed design. The parallel-polarization control for enhanced contrast in high dynamic range imaging has also been validated.