WO2009061756A1

WO2009061756A1 - Bifocal oct system for imaging accommodation of the eye

Info

Publication number: WO2009061756A1
Application number: PCT/US2008/082393
Authority: WO
Inventors: Shuliang Jiao; Jianhua Wang
Original assignee: University Of Miami
Priority date: 2007-11-05
Filing date: 2008-11-05
Publication date: 2009-05-14

Abstract

The present invention advantageously provides a method and system for increasing imaging depth. In particular, the present invention provides an OCT system that includes two or more linked OCT engines operating at different wavelengths to image different depths at different focal planes. The multiple independent images are then combined, to effectively extend the operating depth of an OCT system and thereby provide enhanced eye accommodation research capabilities, as well as the capability to enhance or otherwise extend the imaging depth for other tissue of interest.

Description

BIFOCAL OCT SYSTEM FOR IMAGING ACCOMMODATION

OF THE EYE

FIELD OF THE INVENTION

The present invention relates to coherent waveform based imaging, and more particularly to an optical coherence tomography (OCT) imaging system. BACKGROUND OF THE INVENTION

Accommodation of the eye is the act of adjusting the refractive power to bring objects that are closer to the eye into sharp focus. Accommodation occurs through controlled changes in crystalline lens shape and thickness, and in distances between major refractive surfaces. Accommodation is typically diminished with aging through presbyopia or after the removal of the crystalline lens with surgery. Presbyopia affects almost everyone over the age of 40, and there are currently nearly 2 billion presbyopes worldwide with the world's population aging at an extraordinary rate. In addition, the incidence of cataract is also closely correlated with the age of the population. Cataract affects about 27% of the population aged 65-74 in the United States, and that percentage doubles in the 75-84 age group.

Currently, the best or most often employed practice for the correction of presbyopia includes reading, bifocal, multifocal spectacles, or the less successful use of contact lenses. In addition, treatment for a cataract condition typically includes cataract extraction and intra-ocular lens (IOL) implantation. These conventional approaches suffer from many shortcomings. For example, progressive addition lenses in spectacles, the most successful device for treating presbyopia, may have a limited field of view, include peripheral optical distortion, and/or present aberrations and fixed foci requiring specific head positions to see as various distances. Concentric distance and near zone bifocal contact lenses as well as IO Ls also have problems with ghosting, loss of contrast, haloes and/or compromised vision.

The mechanism of accommodation and its relevance to presbyopia has been the subject of research and debate for decades. Research into understanding accommodation and the development of new systems and techniques for treatment to restore accommodative function has the potential to restore normal vision to a significant portion of the aging population suffering from presbyopia and/or a cataract condition. Optical coherence tomography (OCT) is a non-contact, non-invasive imaging technology that can provide cross sectional imaging of biological tissue, such as structures and components of the eye. OCT provides the advantage of producing non- contact images of the anterior segment of the eye in both static and dynamic conditions. However, commercially available OCT machines suffer from a limited imaging depth. In particular, anterior segment imaging has limited capacity to only provide imaging of the cornea and the anterior surface of the lens, where the imaging depth is approximately 6mm. In addition, such systems are also hampered by their slow imaging speed. The typical 2 frames per second imaging speed makes such systems unsuitable for imaging the dynamic process of accommodation.

The recent development of spectral domain detection techniques make enable OCT systems to provide real time, three dimensional, high resolution imaging of the eye. However, again, current OCT technology has limited imaging depth. With a swept laser light source, current spectral domain OCT techniques can provide an imaging depth no longer than approximately 6mm, which is simply not sufficient to image all the pertinent surfaces of the anterior segment elements.

In view of the above, a quantitative high resolution imaging technique that can image substantially the whole anterior segment, including the cornea, the iris, and the anterior and posterior surfaces of the lens in real time, is highly desired and may greatly benefit research in accommodation. SUMMARY OF THE INVENTION

The present invention advantageously provides a method and system for increasing imaging depth. In particular, the present invention provides an OCT system that includes two or more linked OCT engines operating at different wavelengths to image different depths at different focal planes. The multiple independent images are then combined, to effectively extend the operating depth of an OCT system and thereby provide enhanced eye accommodation research capabilities, as well as the capability to enhance or otherwise extend the imaging depth for other tissue of interest. In particular, the present invention provides an imaging system having a plurality of optical segments, each optical segment including a light source having a wavelength for imaging a focal segment of a specimen, where each optical segment is operable to image a different focal segment of the specimen.

The present invention also provides an imaging system having a first optical segment including a first light source, the first light source having a first wavelength for imaging a first focal segment of a specimen; and a second optical segment including a second light source, the second light source having a second wavelength different from the first wavelength for imaging a second focal segment of the specimen. The imaging system may include a beam combiner in optical communication with the first and second light sources; a hot mirror in optical communication with the first and second light sources; and at least one of the first and second optical segments may include an interferometer. At least one of the first and second light sources includes a super luminescent diode, where the first wavelength may be between approximately 700 nm and 900 nm, and the second wavelength may be between approximately 1200 nm and 1400 nm. The present invention further provides a method of imaging a specimen, including obtaining a first image of a first segment of the specimen with light from a first light source; obtaining a second image of a second segment of the specimen with light from a second light source; and assembling the first and second images into a composite image. BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: FIG. 1 is a schematic of an embodiment of an imaging system in accordance with principles of the present invention;

FIG. 2 is an additional schematic of an embodiment of an imaging system in accordance with principles of the present invention; and

FIG. 3 is an exemplary image obtained through the principles of the present invention. DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an imaging apparatus, such as an OCT system, that is suitable for both time-domain and spectral domain detection and that can further provide an extended or enhanced imaging depth, as well as a high imaging quality along that depth. In particular, the imaging apparatus of the present invention may include multiple imaging segments or optical arms able to image different or varying depths of a particular tissue or biological specimen. Of course, the imaging apparatus and corresponding techniques disclosed herein are equally applicable to non-biological specimen imaging where desired. The imaging apparatus of the present invention generally accomplishes the imaging of varying depths of a specimen or target by using varying light sources having different characteristics, such as differing wavelengths, and may further include multiple reflectors, lenses or other optical components to obtain the desired imaging depth for each imaging portion or segment. The multiple imaging segments may be captured and then visually compiled, merged or otherwise assembled to thereby provide an extended overall imaging depth of a particular specimen that would not be possible with just a single imaging segment as in typical OCT imaging systems.

Now referring to FIG. 1 , a schematic of an embodiment of the imaging apparatus constructed in accordance with the principles of the present invention is shown, generally designated as 10. The imaging apparatus 10 generally may include a plurality of optical "arms" or imaging segment, where each arm or segment provides imaging of a selected depth or focal plane of a particular specimen or target different from the remaining arms or segments to thereby image an entire or substantial depth of the specimen or target. In particular, the imaging apparatus may include a first imaging segment or reference arm 12 providing optical imaging capacity and/or light to a target specimen. The first imaging segment 12 may include a first light source 14, such as a broadband super luminescent diode (SLD), as well as one or more optical components such as lenses, reflecting components, refracting components, or the like in order to manipulate a light path of the first imaging segment as desired.

The light source may be selected based on a predetermined characteristic to provide a desired imaging depth or width, such as a particular wavelength or intensity. In a particular example, the first light source 14 may include a wavelength between 1200nm and 1400nm, such as approximately 1310 nm.

The imaging apparatus 10 may also include a second imaging segment or reference arm 16. The second imaging segment may include a second light source 18, such as a broadband super luminescent diode (SLD), as well as one or more optical components such as lenses, reflecting components, refracting components, or the like in order to manipulate a light path of the second imaging segment as desired. The light source may be selected based on a predetermined characteristic to provide a desired imaging depth or width, such as a particular wavelength or intensity. In a particular example, the second light source 18 may include a wavelength between 700nm and 900 nm, such as approximately 840 nm. The second imaging segment or reference arm 16 may provide an improved imaging depth and dual focus imaging system. Of note, although two arms or segments are shown, it is contemplated that numerous imaging segments, light sources or the like may be employed in accordance with the principles of the invention.

In a particular example, the first and second optical segments or reference arms 12,16 may comprise two independent single-mode optical fiber based interferometers. Optical interferometry combines two or more light waves in an optical instrument in such a way that interference occurs between them to diagnose, analyze, or otherwise exploit the properties of two or more waves. The two sample light beams from the two interferometers may be combined by a beam combiner 20 after exiting the single-mode fibers or particular light source.

After combination, the two beams may be delivered to an eye (or other desired specimen) 22 to be imaged through a scanning and optical system. As discussed above, the imaging arms or segments may include one or more lenses, mirrors, or other optical components 24, 24'. For example, one beam or light path of the imaging apparatus of the present invention (such as OCT beam 2 in FIG. 1 , which may have an exemplary wavelength of 840 nm) may be collimated before the combiner 20, which may be focused closer to the cornea. The other beam (OCT beam 1 in FIG. 1, 1310 nm wavelength) may be diverging, which may be focused into the lens of the eye. A hot mirror 26, which typically includes a specialized dielectric mirror and/or a dichroic filter to reflect infrared light back into a light source while allowing visible light to pass, may be disposed in either and/or both of the light paths of the first and second imaging arms prior to light being delivered or otherwise routed to the target specimen 22, such as a human eye. Where the imaging apparatus 10 is used to image an eye, the system may also include a moving object or target 28 in the line of sight of the eye for imaging during accommodation.

In a particular example, grating based scanning delay line may be used for the time domain system while non-scanning delay line may be used for the spectral domain technique. FIG. 2 shows the principle of an arrangement of the reference arm where the details of the delay line is not shown for the time domain technique. Of note, there is a difference in the path lengths of the two reference arms 12,16 for the two optical/imaging segments or reference arms (such as 6mm, for example), which can be fine adjusted to obtain the desired imaging characteristics. The difference of the path length in the reference arms determines the separation in depth of the two simultaneous OCT image segments 30,30' acquired by the two reference arms or OCT engines. Because the path length difference of the two reference arms may be accurately predetermined, the two OCT images can be effectively merged into one cross sectional image while the effective imaging depth is greatly increased (for example, the imaging depth may be doubled if the difference of the path lengths equals the imaging depth). The imaging apparatus 10 of the present invention may also include electronic and/or imaging system components (not shown) may be included to facilitate the acquisition, processing, and displaying of a particular biological specimen, including but not limited to one or more processors, powers sources, display apparatuses, and/or software applications. In addition, the imaging apparatus 10 may include one or more dual channel data acquisition boards (not shown) for collecting the obtained image data from the plurality of imaging segments or reference arms, and may further be synchronized with the scanning of the sample light to result in the overall synchronized acquisition of the two or more images. Merging of the multiple images can be accomplished and subsequently displayed in real time. In an exemplary method of use of the imaging apparatus 10 of the present invention, a tissue specimen may be positioned proximate the imaging apparatus for imaging. The imaging apparatus 10, as described above, may include multiple imaging segments or arms 12,16 having varying focal planes along the length or depth of the specimen. The arms may be manipulated and/or arranged (i.e., through the selection of a particular wavelength, positioning of the optical components, etc.) such that the position and range of each focal plane abuts or closely approximates an outer edge of the other focal plane(s) of the other reference arms. The specimen may then be imaged, with the multiple images obtained of the varying depths of the specimen then combined or otherwise merged to provide a continuous image of the specimen having a depth or scope much larger than a traditional, single segment OCT system. The different imaging depths may be collected simultaneously using the imaging apparatus 10 and the depth relationship between the images can be predetermined accurately by the arrangement of the multiple reference arms to thereby provide the desired image.

Now referring to FIG. 3, a reconstructed composite image 31 captured using an exemplary imaging apparatus of the present invention is shown. The image in FIG. 3 results from the merging of multiple image segments 32a, 32b, 32c...measured separately at different depths using separate imaging arms. As can be seen in FIG. 3, all of the pertinent surfaces and components of the anterior segment (the front and back surfaces of the cornea, the iris, and the anterior and posterior surfaces of the lens) have been captured and imaged. From the acquired merged image, the curvature, position, and thickness of the cornea, the depth of the anterior chamber, as well as the curvature of the anterior surface and the thickness of the lens can be accurately calculated. In addition, the behavior of the iris at different accommodative conditions can also be imaged.

The imaging apparatus of the present invention increases imaging depth compared to that of conventional OCT devices. The apparatus includes multiple linked optical reference arms or OCT engines operating at different wavelengths to image different focal planes of a tissue specimen, where the captured independent images are then combined to effectively increase the operating depth of an OCT system. Such enhanced imaging depth provides greatly improved capability to monitor dynamic functions of the eye throughout its depth, such as that associated with eye accommodation research. It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope and spirit of the invention, which is limited only by the following claims.

Claims

What is claimed is:

1. An imaging system, comprising: a plurality of optical segments, each optical segment including a light source having a wavelength for imaging a focal segment of a specimen, wherein each optical segment is operable to image a different focal segment of the specimen.

2. An imaging system, comprising: a first optical segment including a first light source, the first light source having a first wavelength for imaging a first focal segment of a specimen; and a second optical segment including a second light source, the second light source having a second wavelength different from the first wavelength for imaging a second focal segment of the specimen.

3. The imaging system of claim 2, further comprising a beam combiner in optical communication with the first and second light sources.

4. The imaging system of claim 3, further comprising a hot mirror in optical communication with the first and second light sources.

5. The imaging system of claim 2, wherein at least one of the first and second optical segments includes an interferometer.

6. The imaging system of claim 2, wherein at least one of the first and second light sources includes a super luminescent diode.

7. The imaging system of claim 2, wherein the first wavelength is between approximately 700 nm and 900 nm.

8. The imaging system of claim 2, wherein the second wavelength is between approximately 1200 nm and 1400 nm.

9. The imaging system of claim 2, wherein the first and second optical segments are optical coherence tomography engines.

10. A method of imaging a specimen, comprising: obtaining a first image of a first segment of the specimen with light from a first light source; obtaining a second image of a second segment of the specimen with light from a second light source; and assembling the first and second images into a composite image.

11. The method according to claim 10, wherein the first light source has a wavelength different from a wavelength of the second light source.

12. The method according to claim 11, wherein the first wavelength is between approximately 700 nm and 900 nm.

13. The imaging system of claim 12, wherein the second wavelength is between approximately 1200 nm and 1400 nm.