Telemedicine screening of retinal diseases with a handheld portable non-mydriatic fundus camera.

BACKGROUND: We modified and reconstructed a high image quality portable non-mydriatic fundus camera and compared it with the tabletop fundus camera to evaluate the efficacy of the new camera in detecting retinal diseases. METHODS: We designed and built a novel portable handheld fundus camera with telemedicine system. The image quality of fundus cameras was compared to that of existing commercial tabletop cameras by taking photographs of 364 eyes from the 254 patients. In all 800 fundus images taken by two camera types, 400 images per camera, were graded with the four image clarity classifications. RESULTS: Using the portable fundus camera, 63% (252/400) images were graded as excellent overall quality, 20.5% (82/400) were good, 11.75% (47/400) were fair, and 4.75% (19/400) were inadequate. Using the tabletop fundus camera, 70.75% (283/400) images were graded as excellent overall quality, 20.4% (51/400) were good, 13.25% (53/400) were fair, and 3.25% (13/400) were inadequate. Common retinal diseases were easily identified from fundus images obtained from the portable fundus camera. CONCLUSION: The new type of non-mydriatic portable fundus camera was qualified to have professional quality of fundus images. The revolutionary screening camera provides a foundational platform which can potentially improve the accessibility of retinal screening programmes.

Projection quality improvement with embedded illumination modulator in projector system.

We demonstrate an approach for improving the image quality for a projector system with a shape-programmable pupil, which could be generated by an illumination modular in which a digital micromirror device is embedded. Essentially, the shaped pupil from the illumination modulator is developed with a dynamically programmable approach to provide aberration compensation for the projection system. By analyzing the optical transfer function, the resolution limit of an imaging system with specific defocus, spherical aberration and coma are shown to be improved significantly with a binary-shaped pupil. It is found that the improvement of the projection quality could be characterized by the scale ratio of K=c/D, defined as the ratio between the resolution scale of structured light, c, and the size scale of the aperture stop, D. When K is equal to 0.05, the low-frequency components of the image could be improved, while if K is equal to 0.3, the imaging quality of the image at high-frequency components can be enhanced in a defocused system. Furthermore, as K ranges from 0.05 to 0.3, the imaging performance of the optical contrast could be enhanced in a projector system with large coefficients of defocused, spherical aberration and coma.

Human Visual System-Based Fundus Image Quality Assessment of Portable Fundus Camera Photographs.

Telemedicine and the medical "big data" era in ophthalmology highlight the use of non-mydriatic ocular fundus photography, which has given rise to indispensable applications of portable fundus cameras. However, in the case of portable fundus photography, non-mydriatic image quality is more vulnerable to distortions, such as uneven illumination, color distortion, blur, and low contrast. Such distortions are called generic quality distortions. This paper proposes an algorithm capable of selecting images of fair generic quality that would be especially useful to assist inexperienced individuals in collecting meaningful and interpretable data with consistency. The algorithm is based on three characteristics of the human visual system--multi-channel sensation, just noticeable blur, and the contrast sensitivity function to detect illumination and color distortion, blur, and low contrast distortion, respectively. A total of 536 retinal images, 280 from proprietary databases and 256 from public databases, were graded independently by one senior and two junior ophthalmologists, such that three partial measures of quality and generic overall quality were classified into two categories. Binary classification was implemented by the support vector machine and the decision tree, and receiver operating characteristic (ROC) curves were obtained and plotted to analyze the performance of the proposed algorithm. The experimental results revealed that the generic overall quality classification achieved a sensitivity of 87.45% at a specificity of 91.66%, with an area under the ROC curve of 0.9452, indicating the value of applying the algorithm, which is based on the human vision system, to assess the image quality of non-mydriatic photography, especially for low-cost ophthalmological telemedicine applications.

Illuminance formation and color difference of mixed-color light emitting diodes in a rectangular light pipe: an analytical approach.

We developed an analytical method of illuminance formation for mixed-color LEDs in a rectangular light pipe in order to derive American National Standards Institute (ANSI) light uniformity, ANSI color uniformity, and color difference of light output using photometry, nonimaging, and colorimetry. The analytical results indicate that the distributions of illuminance and color difference vary with different geometric structures of light pipes and the location of the light sources. It was found that both the ANSI light and the ANSI color uniformity on the exit plane of the light pipe are reduced exponentially with the increase in length of the light pipe. It is evident that a length scale L/A greater than unity assures that the mixed-color LED sources on the entrance plane are uniformly illuminated with acceptable uniform brightness and color on the exit plane of the rectangular light pipe, where L is the length of the light pipe, and A is a constant, which is a geometric parameter for the scale unit of the light pipe's input face. Furthermore, the ANSI light uniformity can be minimized, and the ANSI color uniformity can be maximized under the condition of multilight-source locations P=Q= +/- A/4, where P and Q are the coordinates along the long axis and the short axis, respectively, with one being the entrance plane of the light pipe. We can conclude that the optimum form factor of the light pipe is a square shaped cross section, with the length scale L/A being equal to unity and with multilight sources located individually on positions of A/4 in order to achieve very uniform illuminations with the highest light efficiency and compact package for the optical system with mixed-color LEDs, where L is the length of the light pipe.

Optical transfer functions for specific-shaped apertures generated by illumination with a rectangular light pipe.

We investigated the pupil functions of specific-shaped apertures generated by Lambertian illumination with a rectangular light pipe to derive the corresponding optical transfer functions (OTFs) in aberration-free and defocused optical systems. The semianalytical results indicate that the curves of the OTF of the optical system vary with the form of the shaped apertures that are generated by illumination with different geometric structures of light pipes and light sources. It was found that the OTF values of even-peak frequencies decrease when the Lambertian light source decreases. If there are a total of n x n individual apertures within a pupil, then n near-periodical peaks will appear on the OTF curve. It is evident that the values of the OTF remain almost unchanged even when the lengths of the light pipes are different. Furthermore, the geometric structure of the light pipe does not affect the resolution limit of the optical system, and under the condition of a larger defocused coefficient omega(20), the results of the defocused system can coincide with those of the aberration-free systems.