In recent years, optical coherence tomography (OCT) has been drawing attention. The OCT creates an image representing the exterior or interior structure of an object to be measured using light beams from a laser light source or the like. Unlike X-ray computed tomography (CT), the OCT is not invasive on the human body, and therefore is expected to be applied to the medical field and the biological field, in particular. For example, in the opthalmological field, apparatuses for forming images of the fundus oculi or the cornea have been in practical use.
Patent Document 1 discloses a device using Fourier-domain OCT or frequency-domain OCT. This device irradiates an object to be measured with a beam of low-coherence light, and superimposes the light reflected from the object on reference light to generate interference light. The device then obtains the spectral intensity distribution of the interference light, and applies Fourier transform thereto to acquire an image of the morphology of the object to be measured in the depth direction (z direction). The device includes a galvanometer mirror configured to scan a light beam (measurement light) in a direction (x direction) perpendicular to the z direction, thereby forming an image of a desired area of the object to be measured. The image formed by the device is a two-dimensional cross-sectional image in the depth direction (z direction), taken along the scanning direction (x direction) of the light beam. Such technique using a spectrometer is called “spectral-domain”.
Patent Document 2 discloses a technology, in which measurement light is scanned in the horizontal direction (x direction) and the vertical direction (y-direction) to thereby form a plurality of two-dimensional cross-sectional images in the horizontal direction. Based on the cross-sectional images, three-dimensional cross-section information is obtained for a measurement range. As the three-dimensional imaging, for example, there are a method of arranging a plurality of cross-sectional images in the vertical direction (referred to as “stack data”, etc.), a method of performing rendering on volume data (voxel data) based on the stack data to thereby form a three-dimensional image, and the like.
Patent Documents 3 and 4 disclose OCT devices of other types. Patent Document 3 discloses an OCT device, which scans (sweeps) the wavelengths of light irradiated to the object to be measured, and sequentially detects interference light obtained by superimposing reflected light of each wavelength on reference light to acquire spectral intensity distribution. The device applies Fourier transform to the spectral intensity distribution to form an image of the morphology of the object to be measured. Such an OCT device is called swept-source OCT. The swept-source OCT is a type of Fourier-domain OCT.
Patent Document 4 discloses an OCT device, which irradiates light beams having a predetermined diameter to an object to be measured, and analyzes the components of interference light obtained by superimposing the reflected light on reference light. Thereby, the device captures an image of the object to be measured in a cross-section perpendicular to the traveling direction of the light. Such an OCT device is called full-field OCT or en-face OCT.
Patent Document 5 discloses a configuration in which OCT is applied to the ophthalmologic field. Incidentally, before the application of OCT, a fundus camera, a slit lamp, a scanning laser opthalmoscope (SLO), or the like has been used as a device for observing the subject's eye (see, for example, Patent Documents 6, 7, and 8). The fundus camera is a device that irradiates the subject's eye with illumination light and receives the light reflected from the fundus to thereby capture an image of the fundus. The slit lamp is a device that cuts out an optical section of the cornea using a slit light to thereby acquire an image of the cross-section of the cornea. The SLO is a device that scans the fundus with a laser beam, and detects its reflected light with a high-sensitivity element such as a photomultiplier tube for imaging the morphology of the fundus surface.
The devices using OCT offer advantages with respect to the fundus camera in that they can acquire high-resolution images, and also that they can obtain cross-sectional images as well as three-dimensional images.
As described above, the devices using OCT can be used for the observation of different parts of the eye, and are capable of acquiring high-resolution images. Therefore, the OCT devices have been applied to a variety of ophthalmic diseases. For example, there has been a known device, which is made of a combination of an OCT device and a subjective visual acuity test device, and provides materials for the diagnosis of maculopathy and glaucoma (see Patent Document 9).
[Patent Document 1] Japanese Unexamined Patent Application Publication No. Hei 11-325849
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2002-139421
[Patent Document 3] Japanese Unexamined Patent Application Publication No. 2007-24677
[Patent Document 4] Japanese Unexamined Patent Application Publication No. 2006-153838
[Patent Document 5] Japanese Unexamined Patent Application Publication No. 2008-73099
[Patent Document 6] Japanese Unexamined Patent Application Publication No. Hei 9-276232
[Patent Document 7] Japanese Unexamined Patent Application Publication No. 2008-259544
[Patent Document 8] Japanese Unexamined Patent Application Publication No. 2009-11381
[Patent Document 9] Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2011-515194