Patent Application
20070146634
The present invention is directed to a system and method for performing a laser ophthalmic surgical procedure, and, more particularly, to a system and method for adjusting an illumination characteristic during the surgical procedure.
Reflections can have a negative impact on image processing, especially if reflections mask an important part of the image. For example, in ophthalmic devices it is sometimes necessary to detect and locate features of an eye such as a pupil. One or more illumination sources are typically necessary in order to achieve sufficient image brightness. These sources can be visible in the image of the eye and can cause problems in locating the desired features. For example, a laser refractive surgery system can have an illumination arrangement that places the sources near the optical axis of the camera. This would cause reflections from the cornea close to the pupil boundary, so that this boundary would be difficult to detect. The problem is exacerbated if a corneal flap is cut on the eye, as the size of the illumination source reflection grows owing to the roughening of the corneal surface. However, if the illumination source is far off-axis, accessibility to the patient is reduced, as is the user's working area.
As a particular goal of laser surgical systems is to provide maximum patient access, it is believed desirable to place illumination sources within a predetermined volume, wherein reflection can affect the image. However, another goal of refractive surgery is to operate on undilated eyes, wherein the pupil is small. For small-spot refractive surgery systems, stabilizing the eye is critical for best outcomes. Tracking undilated eyes demands a determination of pupil size, in which case the area around the pupil must be free of distractions. For large pupils, some obscuration is permissible, since the large perimeter of the pupil allows accurate sizing, with only a portion being obscured. Small pupils, however, can be obscured, which makes them more difficult to track in the presence of distractions. For the present purposes, the transition from “small” to “large” occurs at approximately 4 mm. Therefore, it is preferable that no reflections occur in the image within 4 mm of the pupil center.
Therefore, it would be desirable to provide a system and method of reducing the impact of reflections on an image, by, for example, reducing the intensity of such reflections, without impacting the user's view during critical portions of the procedure.
The present invention is directed to a system and method for optimizing the effects of light sources on viewing and image processing, and for imaging an illuminated object. The system takes advantage of the fact that specularly reflected light (glint) has particular polarization properties compared with diffusely scattered light. The system can comprise means for delivering polarized light to illuminate an object with a polarized beam and means for delivering unpolarized light to illuminate the object with an unpolarized beam. A detector is positioned to receive light from the polarized and the unpolarized beams reflected from the object. A polarizer is positionable upstream of the detector and downstream of the object, and is oriented for substantially filtering out specular reflection from the object and for permitting at least a portion of diffuse reflection from the object to pass therethrough. Means are provided for controlling the polarized and unpolarized light delivering means and the polarizer for selectively illuminating the object with and detecting light having a selected polarization characteristic as a function of a portion of a procedure being performed.
The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.
A detailed description of preferred embodiments of the invention will now be discussed with reference to
In an embodiment, the first light source 11 is adapted to emit a polarized light beam 19, for which a first polarizer 20 is positioned downstream of the first light source 11, and a second polarizer 21 is positioned upstream of the detector 18 and downstream of the eye 14. The second polarizer 21 is oriented for substantially filtering out specular reflection from the eye 14 and for permitting at least a portion of diffuse reflection from the eye 14 to pass therethrough. The first 20 and the second 21 polarizers in a particular embodiment can be selected from a group consisting of a pair of crossed linear polarizers and a pair of circular polarizers, although these are not intended as limitations.
In an embodiment, the first 21 and the second 22 polarizers are removably positioned for permitting the detection of unpolarized light at the detector 18. In this system 10, the first 11 and second 12 light sources can comprise a unitary device (
Either or both of the first 11 and the second 12 light sources may be operated on by the controller 15 to activate them, adjust their brightness, or move them relative to the eye 14. In addition, the first 11 and the second 12 light sources may be have variable or predetermined spectral composition.
A particular embodiment of a method of the present invention comprises laser refractive surgery on the cornea 13. Such a procedure is typically carried out in a plurality of stages, wherein different illumination characteristics may be optimal in each stage. For example, if a corneal flap is cut initially to expose underlying stroma, as is known in the art, unpolarized light reflects off the flap and the hinge, causing a “glint” that can be detrimental to eye tracking and image processing systems. However, this glint is useful for locating the flap and hinge.
Thus a hybrid system 10,10′ can be adapted to provide one or both of polarized 19 and unpolarized 23 beams for different parts of the procedure, and also for different entities receiving the beams 19,23. A user viewing the eye 14 through a magnifying device 24 may prefer to see an image illuminated with an unpolarized beam 23 first in order to view the hinge, and then switch to a polarized beam 19 to cut down the glint. Data sent from an image created with an unpolarized beam 23, however, may be noisy and thus less than optimal for the image processing software 17, and thus during the procedure it may be preferable to use illumination from a polarized light source 11. The image processing software 17 can also typically send an image to a display 25 for viewing by the user.
Additional control may further be provided by permitting the light sources 11,12 to be moved during the procedure in order to optimize a placement of reflections relative to the detector 18.
Another variable parameter can comprise an ability to adjust other illumination characteristics, such as the wavelength composition of one or both of the beams 19,23. Such control would enable, for example, an enhanced viewing of blood vessels with green light during certain portions of the procedure but not during other portions. For example, the blood vessels may be used during alignment of two eye images, but then not be important to see in an enhanced fashion during flap cutting. In another example, if registration marks are made on the eye, the marking ink can have certain predetermined reflection characteristics that can be optimized relative to an illumination beam 19,23 for improving visualization thereof. In yet a further example, both types of illumination 19,23 may be used simultaneously, with a brightness of one different from the other in order to, for example, still view the glint but to a lesser extent compared with the polarized reflection.
In the foregoing description, certain terms have been used for brevity, clarity, and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for description purposes herein and are intended to be broadly construed. Moreover, the embodiments of the system and method illustrated and described herein are by way of example, and the scope of the invention is not limited to the exact details of construction and use.
Having now described the invention, the construction, the operation and use of preferred embodiments thereof, and the advantageous new and useful results obtained thereby, the new and useful constructions, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.
