Conference Paper

Optical Design of a Compact Image Acquisition Device for Mobile Diabetic Retinopathy Screening

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... These smartphones possess the flexibility to control the light source, compatible with existing camera applications (Apps), good quality of the back-facing camera that produces a high resolution of an image. Therefore, an Android-based smartphone is the best choice for interplatform compatibility and flexibility range for prototyping [9,10]. The external illumination design of the external optical system consists of two lens arrangements: i) condenser lens (inside the smartphone) and ii) aspheric lens (focusing lens) that must be aligned with the smartphone camera, as illustrated in Fig. 2. In the figure, show a single piece of the custom lens (aspheric) was assembled to be aligned [11,12] with a smartphone camera lens (condenser lens) that emits a flash (white LED is used as a light source) that will deflect the illumination path of the desired FOV. ...
... Pre-designer software Pre-Designer is a simple utility open-source software that was developed by LINOS Photonics to provide a straightforward design at the fundamental stage of pre-design in an optical imaging system [14]. The basic parameter and field requirements needed in the desired illumination system are i) focal length, ii) object or image distance, and iii) object height [9]. The angular magnification, ݉ in Eq. (1) represents the power of the human eye (Diopter of lens). ...
Conference Paper
Full-text available
This paper presents an illumination system based on indirect ophthalmoscopy for smartphone ophthalmoscope to support retinal imaging photoplethysmography (iPPG) assessment. An experimental demonstration is carried out to measure the light source profile of smartphones and portable fundus camera. An illumination system: i) external illumination system of a smartphone with two lens arrangement and ii) internal illumination system of the eye. The illumination systems are demonstrated using Pre-designer and Winlens 3D open-source software. The outcome of experimental work shows that the smartphone exhibited a similar light source spectrum as a fundus camera with slightly high-power intensity. The illumination systems showed a good convergence of spot diagram at the centre of a FOV with a fair resolution of the Gaussian beam. The quality of the produced image depends on the choice of lens, lens arrangement, desired stopper distance, and focal length setting. The outcomes are essential to implement a high coverage fundus image of a smartphone ophthalmoscope prototype that increases its screening reliability. Keywords-Smartphone ophthalmoscope, retinal imaging photoplethysmography (iPPG), illumination system, fundus camera, field-of-view (FOV).
... The path that describes how the rays illuminate the retina is called illumination path and the path describing how the rays go from the retina to the camera is called imaging path. [12] In this study, we will focus on the problem of calibrating a fundus camera. A calibrated fundus camera provides more information to be extracted on the 3D structure of fundus components, giving ophthalmologists more possibilities to identify anomalies and assist in diagnosis. ...
... Since and are orthogonal, we obtain: (12) (13) These are the two fundamental constraints on the intrinsic parameters for a homography. ...
Article
This paper presents a novel hybrid method for the determination of intrinsic geometric parameters in the case of a fundus camera from a set of acquired images. The main idea is to integrate two camera calibration methods, the most popular in the field of computer vision, Agapito and Zhang, by means of the optimization procedure. In comparison with traditional techniques suffering from a possible degeneration of algorithms, the proposed approach gives satisfactory results and has demonstrated the expected performance improvements in terms of efficiency and robustness.
... The fixation targets and the aid of an eyecup allows the autofocus feature to run, enabling the correction of refractive errors that may be present in the eye [42], caused by myopia or hyperopia. While the EFS optical formula was designed to cope with distinct levels of dioptres [43], it is essential to achieve a well-focused image of the retina without having to manually change the distance between optical elements, a feature that often requires additional operator training. ...
Article
Full-text available
Diabetic Retinopathy is a complication of diabetes that can cause severe vision impairment or even blindness. The condition is treatable in early stages, but it often progresses asymptomatic and undetected. Once the symptoms become noticeable, damage in the retina might already be permanent, thus many countries have implemented retinal imaging screening programmes for their diabetic population. However, existing screening programmes are not reaching all patients, and Diabetic Retinopathy stands as a leading cause of preventable blindness in the active population. We contend that the existing technological infrastructures and clinical processes may be hindering the coverage of Diabetic Retinopathy screening programmes. This paper presents EyeFundusScopeNEO, a Tele-Ophthalmology system based on a screening information system and a mobile fundus camera, which shall support opportunistic and planned screening in primary care, using cameras that are handheld, non-invasive, avoid drug-induced pupil dilation, are usable by clinicians who are not specialised in Ophthalmology, and that cost a fraction of existing table-top fundus cameras. Preliminary studies indicate the potential of the system to increase the reach of screening programmes and clinical research field trials are under preparation.
Chapter
Imaging the eye retina is critical to diagnose various pathologies, particularly Diabetic Retinopathy, which is the leading cause of avoidable blindness in the world. The image acquisition through tabletop fundus cameras is the preferred method for retinopathy screening. However, these devices require expertise for operation, limiting its broad application. In this paper, two handheld fundus camera prototypes developed by Fraunhofer AICOS (EyeFundusScope Compact and EyeFundusScope Standard) have their optical capabilities compared, not only between each other but also with another commercially available camera. Field-of-view measurements are performed, as well as a subjective analysis on eye model images acquired with each of prototypes. Besides the comparison between handheld devices in the same experimental setup, conceptual specification on the prototype and optical system for the Compact version are described in order to demonstrate the most relevant issues to be considered when developing a valuable instrument for diabetic retinopathy screening and diagnosis.
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