Delivering a short Arc lamp light for eye imaging

#Arc lamps have been used in many applications, including camera strobes, analytical instrumentation, surgical illumination, theatrical lighting, and laser and machine vision. In spite of the availability of other more convenient and low cost light sources such as LEDs (light emitting diodes), Arc lamps are still currently used in some niche areas because they have certain unique properties that other light sources cannot provide. These include high brightness, high power, high UV (ultra violet) light content, a wide continuous spectral distribution with excellent color balance and spectral flatness in the visible region, long life, and stable spectrum over life.

#Arc lamps have two operation modes, namely DC and pulsed mode. The DC operation mode generally has a better arc stability and substantially longer life. However, this mode of operation is not ideal for photography, which only needs a short flash of illumination light while a photo is being taken. As for the pulsed mode of operation, the combination of wide spectrum and color balance with the ability to produce short pulses of high brightness light has made Arc lamps particularly suitable for biological photography, enabling excellent color projection and high-quality flesh tones. In this respect, short-arc flash lamps with an arc spacing of typically 1-3 mm are especially unique because they can provide pulses of high intensity and brightness light that other light sources cannot match. The high brightness and intensity is particularly desirable for superior camera performance. In addition, a short-arc flash lamp can also solve the problem of motion of a living biological sample such as a human eye and hence eliminate blurring of the obtained image. Furthermore, the wide spectral distribution of Arc flash lamps also makes them ideal for applications requiring light in specific spectral regions, such as red-free images and Fluorescein Angiography. The specific spectral region can be selected by placing different types of optical filter in the illumination and/or detection light path.

#In spite of its wide use in biological imaging applications, the structure of an Arc lamp makes it difficult to efficiently collect the emitted light and deliver it to the object to be imaged with excellent uniformity. In general, the discharge formed between the two Arc lamp electrodes is a wandering but relatively linear light source. An ellipsoidal reflector can be used for relatively high efficiency light collection, and in such a case the lamp is usually aligned along the optical axis, with the arc at the first focus. A fiber optic bundle is usually placed with its input end at the second focus to collect the light. Although this arrangement focuses a relatively large portion of the available light from the arc, since the electrode will obstruct the light at angles of less than about 30 degrees from the optical axis, there is little light converging into the fiber bundle at angles close to the optical axis. This will cause problems in terms of light illumination uniformity for eye fundus imaging.

#FIG. 1 shows an embodiment of a light collection and homogenization configuration;

#FIG. 2 shows an example of the use of a solid optically transparent cone as the ring beam transformer;

#FIG. 3 shows an example of the use of a convex conical surface mirror as the ring beam transformer;

#Novel embodiments of optical configurations and methods are described for collecting and conditioning light from a single remotely located axially linear light source that can supply both continuous and pulse illumination. The conditioned light is transmitted through an optical fiber bundle and/or used directly as the light source for observing and imaging the anterior/posterior chamber of the eye in an optical system. In one embodiment, before being projected into the eye, the light beam is manipulated and spatially filtered, and eventually transformed into a light beam of ring shape. The ring illumination beam can then be co-axially projected onto the posterior part of a human eye and the light beam has a sufficiently large relatively uniform angular flux distribution so that a wide area on the retina of the eye can also be uniformly illuminated.

#In another embodiment, a light homogenizer is combined with a ring beam transformer for a remotely located arc lamp. The light homogenizer improves the spatial and angular uniformity for a light beam collected from an arc lamp. The ring beam transformer efficiently converts optical radiation from a linear light source into a light beam of ring shape. Another embodiment is the direct collection of light from a linear light source using a curved surface mirror and spatially filtering the light beam into a desired ring beam having a desired numerical aperture.

#Reference will now be made in detail to various embodiments of the invention. Examples of these embodiments are illustrated in the accompanying drawings. While the invention will be described in conjunction with these embodiments, it will be understood that it is not intended to limit the invention to any embodiment. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the various embodiments. However, the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.