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LEDs Illuminate Eye for Ocular Disease Screening

A new imaging system using six different wavelengths to illuminate the interior of the eyeball (ocular fundus) may pave the way for doctors to easily screen patients for common diseases of the eye, such as age-related macular degeneration and diabetic retinopathy. The system is described in the journal Review of Scientific Instruments, which is published by the American Institute of Physics.

Currently, when optometrists and ophthalmogists visualize the ocular fundus, they typically take snapshot images of the eye in two or three wavelengths (red, green and blue), which can reveal some visually-apparent abnormalities. But an added dimension made possible with the imaging system described by Nicholas L. Everdell of University College London allows doctors to distinguish between the different light absorbing characteristics of biological molecules called chromophores.

According to the paper's coauthor Iain Styles of the University of Birmingham, five of these light-absorbing compounds are prevalent in the eye: retinal hemoglobins, choroidal hemoglobins, choroidal melanin, RPE (retinal pigment epithelium) melanin, and macular pigment. In a separate paper (Medical Image Analysis 10 (2006) 578–597), Styles said that each of these has been shown to give rise to distinct variations in tissue coloration that can be discriminated in multispectral images.

In the new work, Everdell and Styles describe a device combining a high-sensitivity CCD camera with wavelength-specific illumination from LEDs (light-emitting diodes) that provides multispectral images of the ocular fundus. The multispectral images, explains Styles, are affected differently by the pigments present in the eye, and through a sophisticated algorithm they can be used to generate a pixel-by-pixel "parametric map" of the distribution of substances in the eye. Such maps may allow primary care clinicians to screen for and identify pathologies at a much earlier stage of development than other imaging modalities.

An advantage the new system offers over other multispectral retinal imaging systems is its speed. It can acquire a sequence of multispectral images at a fast enough rate (0. 5 seconds) to reduce image shifts caused by natural eye movements. In contrast with snapshot systems, the system's images retain full spatial resolution. Also, the system uses only the specific wavebands that are required for the subsequent analysis, minimizing the total light exposure of the subject, ensuring patient safety and improving image quality.

"The long term goal," Everdell said, "is to develop a system for chromophore quantification that is an integral part of the standard fundus camera, and therefore could be used routinely by both optometrists and opthalmologists."

The article, "Multispectral Imaging of the Ocular Fundus using LED Illumination" by Nicholas Everdell, Iain B. Styles, Antonio Calcagni, Jonathan Gibson, Jeremy C. Hebden, and Ela Claridge will appear in the journal Review of Scientific Instruments. See:

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Image Caption: Parametric map showing the distribution of hemoglobin in a section of the retina.

Review of Scientific Instruments, published by the American Institute of Physics, is devoted to scientific instruments, apparatus, and techniques. Its contents include original and review articles on instruments in physics, chemistry, and the life sciences; and sections on new instruments and new materials. One volume is published annually. Conference proceedings are occasionally published and supplied in addition to the Journal's scheduled monthly issues. RSI publishes information on instruments, apparatus, techniques of experimental measurement, and related mathematical analysis. Since the use of instruments is not confined to the physical sciences, the journal welcomes contributions from any of the physical and biological sciences and from related cross-disciplinary areas of science and technology. See:
The American Institute of Physics is a federation of 10 physical science societies representing more than 135,000 scientists, engineers, and educators and is one of the world's largest publishers of scientific information in the physical sciences. Offering partnership solutions for scientific societies and for similar organizations in science and engineering, AIP is a leader in the field of electronic publishing of scholarly journals. AIP publishes 12 journals (some of which are the most highly cited in their respective fields), two magazines, including its flagship publication Physics Today; and the AIP Conference Proceedings series. Its online publishing platform Scitation hosts nearly two million articles from more than 185 scholarly journals and other publications of 28 learned society publishers.

Jason Socrates Bardi | Newswise Science News
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