Patent Application
20080084541
According to an exemplary aspect, the light source 101 is a laser that produces a relatively narrow laser beam 111 with a predetermined beam size, power, and wavelength. Illustratively, the beam size at the diffuser 102 will be about 0.1-0.5 mm. The laser source 101 may particularly be a diode laser module, which is advantageous due to compact size, high reliability, and low cost. Other coherent or semi-coherent light sources that provide high brightness, such as a super luminescence diode (SLD), may be used. A suitable diode laser module for the exemplary application will have an output power of 0.1-10 mW at a wavelength in the near-infrared range of between about 760 to 1000 nm.
In an exemplary aspect, the diffuser 102 will be a rotating holographic diffuser such as that disclosed in U.S. Pat. No. 6,952,435, the disclosure of which is herein incorporated by reference in its entirety to the fullest allowable extent. The holographic diffuser can be made with a fine and uniform holographic pattern embossed on a thin acrylic substrate or other suitable material. The exemplary holographic diffuser 102 will particularly have a small but well-defined diffusing angle in the range of about 0.5 to 5 degrees. It may be desirable to focus the source light on the diffuser. A motor 106 is connected to the diffuser 102 to rotate or otherwise scan the diffuser across the laser beam 111. This serves to randomize the relative phase across the laser beam and minimize or eliminate speckle due to coherence effects.
The first pinhole aperture 103 is located along the system optical axis 139 immediately optically downstream of the holographic diffuser 102. It is illuminated with the diffused laser light output 115. The exemplary first pinhole aperture 103 has a circular diameter between about 50 to 200 micron.
As illustrated, the optical component 104 is a focal lens that refocuses the light 112 transmitted through the first pinhole aperture 103 into a probe beam 113. The focal lens 104 is positioned, and has optical parameters, such that it forms an image 103′ of the first pinhole aperture 103 onto a first predetermined image plane, which in the illustrative embodiment is the anterior corneal surface 201 of the subject's eye. The probe beam spot on the cornea 201 is thus confined by the image size 103′ of the first pinhole aperture 103. In the exemplary embodiment, the focal lens 104 has a focal length of between about 30 to 100 mm. The working distance from the focal lens 104 to the first image plane 201 is between about 150 to 300 mm. Other focal optical components may be used to perform the desired function, and may include diffractive or holographic components, for example.
The second pinhole aperture 105 is located adjacent the front surface of the focal lens 104 and is illuminated by the probe beam 113 formed by the focal lens. Alternatively, the second pinhole aperture could be located adjacent the rear surface of the focal lens 104 as shown at 105′ and be illuminated by the diffused light output 112. In the exemplary embodiment, the second pinhole aperture has a circular diameter between about one (1) to four (4) mm, which limits the vergence of the laser probe beam 113 propagating to the subject's eye 200. A small vergence of the laser probe beam 113, advantageously being equal to or less than about five (5) milliradians, minimizes the beam size change around the focal plane. Thus the size of the probe beam spot 204 on the retina 203 remains substantially the same for subjects' eyes with various defocusing powers over a range of about 25 diopters between about +10 to −15 diopters. It will be appreciated that in such embodiments aperture 105, 105′ and lens 104 are configured and arranged such that the size of the probe beam spot 204 remains substantially the same when used with such subjects. The term “substantially the same spot size” means that the spot does not vary by more than 50% in diameter.
A person skilled in the art will appreciate that the second pinhole aperture 105 is more or less imaged as the probe beam spot 204 onto the second predetermined image plane; that is, the retina 203, via the eye's optics. As such, the laser probe beam 113 has a beam spot 204 confined by the image size of the second pinhole aperture 105. The probe beam spot size 204 at the second predetermined image plane location 203 advantageously will have a diameter in a range between about 70 to 130μ and, more advantageously, a diameter of about 100μ. Since the laser probe beam 113 is a diffused laser beam, the beam spot 204 on the retina 203 will not have an over-tight focus as that term is known in the art. In the illustrative embodiment, the eye, comprising the cornea, a natural or artificial lens, and the retina, represents a focusing optical subsystem. The cornea (the first predetermined image plane) can be considered to be about 20 mm in front of the retina (the second predetermined image plane).
According to an exemplary embodiment described with reference to
In a further aspect according to the instant embodiment, as illustrated in
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Another embodiment of the invention is directed to an ophthalmic method. According to an aspect, the ophthalmic method is particularly suited to providing a diagnostic wavefront probe beam and, further, to utilizing this wavefront probe beam for measuring a wavefront aberration of a subject's eye. The ophthalmic method includes the steps of providing an at least semi-coherent beam of light along a source light path; randomizing the spatial coherence of the at least semi-coherent beam of light to produce a diffused light output beam; illuminating a first pinhole aperture with a portion of the diffused light output beam; forming a probe beam from the diffused light output beam and imaging the first pinhole aperture at a first predetermined imaging location; and illuminating a second pinhole aperture with either the diffused light output beam or the probe beam, depending upon its placement, to control a vergence of the probe beam and a size of the probe beam spot at a second predetermined imaging location. The method may further include the step of providing a focusing optical subsystem having an anterior surface that can be positioned at the first predetermined imaging location and another surface that will coincide with the second predetermined imaging location. According to an exemplary aspect, a subject's eye is provided as the focusing optical subsystem in which the anterior corneal surface is the surface positioned to coincide with the first predetermined imaging location, and the retinal surface of the eye is the other surface that will coincide with the second predetermined imaging location.
In conjunction with the system embodiments described above, the various method steps can be carried out in the following various exemplary manners. A laser (laser diode) or a super luminescent diode can be used for providing the at least semi-coherent beam of light. A scanning or rotating holographic diffuser can be used for diffusing the at least semi-coherent beam of light. A focusing lens can be used for imaging the first pinhole aperture at the first predetermined imaging location. As noted above, a properly positioned and stabilized eye will provide the focusing optical subsystem in which the anterior corneal surface becomes the first predetermined imaging plane and the retina is the second predetermined imaging plane. According to the method, the characteristics of the second pinhole aperture are used to control a vergence of the probe beam as it propagates towards the eye and a size of the probe beam spot at the second predetermined imaging location. A probe beam image spot (first pinhole aperture image) has a diameter equal to or less than about 500μ on the anterior corneal surface, and the probe beam spot formed on the retinal surface has a diameter in a range between about 70 to 130μ. A wavefront sensor and, in particular, a Hartmann-Shack apparatus can be used to measure wavefront aberration of the subject's eye. The probe beam can be directly injected into the subject's eye. The probe beam can also be injected off-axis into the subject's eye along a probe beam propagation axis that is displaced relative to an optical/instrument axis.
The foregoing description of the preferred embodiments of the invention have been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teachings. It is intended that the scope of the invention embodiments be limited not by this detailed description but rather by the claims appended hereto.
