Patent Application
20070270673
The present invention relates generally to measuring ocular parameters, e.g., related to ocular perfusion and/or pressure. The invention can be used to monitor cerebral perfusion, central circulatory flows or eye health, or to detect the onset of various conditions, including certain post-operative complications.
Ocular parameters, such as parameters related to ocular perfusion (e.g., oxygen saturation of the retina or fundus), may be monitored for a variety of reasons. Ocular perfusion provides a direct indication of eye health and may therefore be monitored to identify potential eye disease or deterioration. For example, ocular perfusion may be monitored to detect hypoxia of the retina or ONH, which has been linked to a variety of ocular vascular disorders. However, ocular perfusion may also be monitored, for example, as an indication of cerebral perfusion, central circulatory flows or to identify potential surgical complications.
With respect to cerebral perfusion, it has been recognized that retinal oxygen saturation is well correlated to cerebral blood flow. There are a variety of contexts in which it may be desired to monitor cerebral blood flow or, more particularly, to monitor the perfusion and oxygenation of each side of the brain relative to systemic perfusion. For example, monitoring cerebral blood flow is of direct interest in connection with a variety of conditions such as Closed-Head Injuries, cerebral aneurysm, strokes (DVAs) or other conditions involving loss of neuronal function due to disturbance in cerebral perfusion. Cerebral perfusion may also be monitored in connection with a variety of medical conditions/procedures, including: heart surgery (e.g., CABG, ablation for treatment of atrial fibrillation, aortic valve surgery) and coronary grafts, carotids, neck surgeries, aneurysm surgeries, anything done in the upright or sitting position, cerebrovascular disease, cognitive deficits, etc. In addition, because central circulatory flows, including to the retina, are preserved in certain medical conditions where peripheral flows may be compromised, monitoring ocular perfusion and oxygen saturation may be useful to supplement or supplant conventional finger or other extremity oxygen saturation measurements in appropriate cases.
Identifying potential post-operative complications, including post-operative visual loss (POVL), is also a significant concern. Surgical complications exact a considerable toll on patient health and quality of life, in addition to increasing healthcare costs by extending treatment, requiring longer hospital stays, and creating economic and personal hardship due to death and disability. A 2003 study published in the Journal of the American Medical Association reviewed postoperative complications and 18 types of medical injuries during hospitalization. The study concluded that the events accounted for 2.4 million additional hospital days and $9.3 billion in excess charges each year. In the same year of study's publication, the Centers for Medicare & Medicaid Services (CMS) and the Centers for Disease Control and Prevention (CDC) formed the Surgical Care Improvement Project (SCIP) with ten other national organizations. In 2005, they announced an ambitious goal of improving the safety of surgical care by reducing post-operative complications 25% by 2010.
Because the large numbers of spinal operations are increasing each year and the operations themselves are increasing in complexity, it is critical to minimize surgical complications from back operations. Over 320,000 back operations are performed each year in the United States, including discs, lumbar laminectomies and fusions of lumbar and thoracic spine. These procedures are expected to increase as the population ages. As much as 80% of the U.S. population will be affected by back pain at some time during their lives. According to injury statistics from the US Bureau of Labor Statistics, there were 303,750 work-related back injuries in 2003. The aging process itself can lead to back pain that may require treatment and surgery, and because people today are living longer, the number of patients with back pain increases every year. Members of the Baby Boom generation will be the largest population of older adults in history who may require joint and back treatment or surgery.
Anesthesiologists have led the way in improving surgical outcomes in the United States through early detection of parameters that lead to adverse outcomes. In July 1999, The American Society of Anesthesiology (ASA) Committee on Professional Liability established the ASA POVL registry, which recognized POVL as a significant concern with an apparent increase in incidence. One possibility for the apparent increase in incidence in blindness, in spite of the absence of concrete incidence data, is related to an increase in longer spine surgeries occurring in the last ten years. Malpractice awards for POVL are often over $250,000.
Criteria for POVL include an acute deficit in vision not attributable to other causes for visual loss, which is usually noticed immediately after surgery. The blindness may be bilateral (50%) and in some cases partially reversible (44%). Patients may have complete blindness; partial blindness with diminished visual acuity, field deficits and loss of color vision. This complication probably relates to optic nerve ischemia (caused by visual system arterial insufficiency or visual system venous hypertension) but also may be a result of direct pressure on the eye during surgery. There is currently no accepted and effective mechanism for preventing this complication. As discussed below, it has been recognized that monitoring ocular parameters, including ocular perfusion/saturation and/or pressure, provides a mechanism for detecting the onset of such complications.
The present invention is directed to devices and associated methodology for monitoring one or more ocular parameters such as ocular perfusion, oxygen saturation and/or pressure. As noted above, these parameters may be monitored in relation to analyzing eye health, central circulatory flows, cerebral conditions or other conditions. Moreover, the parameters may be monitored in relation to a medical procedure (e.g., before, during and/or after) or independent of any such procedure. For example, the invention can be used to monitor a patient during a medical procedure to identify a condition indicative of the possible onset of blindness or damage to the patient's eye or eyes. This provides an opportunity for the caring physicians to address the condition, e.g., by repositioning the patient or otherwise attempting to increase perfusion and oxygen saturation of the retina or fundus, thereby potentially reducing the occurrence or severity of such complications.
The structure and methodology of the invention may also be used to monitor eye health and patient health in other contexts. For example, as noted above, because ocular perfusion is a good indication of central circulatory flows, ocular perfusion may be monitored in lieu of or in addition to extremity measurement in certain cases. Relatedly, because retinal oxygen saturation is well correlated to cerebral blood flow, measurements performed on the patient's eye in accordance with the present invention may be useful in noninvasively monitoring cerebral conditions with greater confidence. Moreover, a variety of conditions related to eye diseases or deterioration may be identified or analyzed using the devices and processes described herein. In addition, the processes discussed below may be used in conjunction with other technologies, including certain existing ophthalmology technologies, for improved patient monitoring and diagnosis. For example, the processes described below may be useful together with fluorescent angiography to determine if there has been damage to one of the layers of the retina.
Some interesting background discussion and related technology is discussed in: de Kock, et al., Reflectance Pulse Oximetry Measurements from the Retinal Fundus, IEEE Transactions on Biomedical Engineering, Vol. 40, No. 8, August 1993; and Khoobehi, et al., Hyperspectral Imaging for Measurement of Oxygen Saturation in the Optic Nerve Head, Investigative Ophthalmology & Visual Science, Vol. 45, No. 5, May 2004. In particular, these articles discuss various methodologies for analyzing ocular perfusion and oxygen saturation and certain structure for implementing those methodologies. However, those articles are not directed to post-procedure blindness and do not utilize fiber optic technology as set forth herein.
In accordance with one aspect of the present invention, a method and apparatus (“utility”) is provided for monitoring ocular perfusion and/or oxygen saturation. As noted above, it may be desirable to monitor ocular perfusion or oxygen saturation in connection with certain medical procedures. In addition, there may be other circumstances where it is desired to monitor ocular perfusion or oxygen saturation, e.g., after eye surgery or otherwise to monitor eye health. The utility involves an optical instrument for use in monitoring patient perfusion and/or oxygen saturation and a positioning structure for positioning at least a portion of the optical instrument so as to monitor the noted ocular parameter(s). For example, the optical instrument may include an optical transmitter assembly for transmitting an optical signal in relation to tissue of a patient's eye and an optical receiver assembly for receiving the optical signal after interaction with the tissue, e.g., reflection from the tissue area. Such a device may further include a processor for providing information regarding perfusion or oxygen saturation. For example, perfusion or oxygen saturation may be monitored based on measurements of signal attenuation at one or more wavelengths. A variety of algorithms have been developed in this regard. The positioning structure may include an eye contact for maintaining the instrument portion in a substantially fixed position in relation to a retina of the patient. For example, the instrument portion may include a fiber end for transmitting or receiving the optical signal. Alternatively or additionally, the utility may include headgear, e.g., in the form of eye glasses or virtual realty-style headgear, for reducing ambient light interference and/or providing the noted positioning structure.
In accordance with another aspect of the present invention, a fiber optic pathway is used in performing imaging spectroscopy to determine oxygen saturation, e.g., of ocular or other tissue. An associated apparatus comprises an imaging system for obtaining at least one image of tissue of interest; at least one fiber optic pathway disposed between the imaging system and the tissue of interest for use in obtaining the image(s); and a processor for processing the images to obtain information regarding the oxygen saturation of the tissue of interest. The fiber optic pathway(s) may be used to transmit light to the tissue of interest and/or transmit reflected light from the tissue of interest to an optical receiver (e.g., a camera). The processor may be operative for digitally subtracting images corresponding to different wavelengths and to correlate the result to an oxygen saturation value. In this regard, the processing may effectively combine reflectance imaging and oximetry.
In accordance with one aspect of the present invention, a utility is provided for use in detecting a potential onset of patient blindness. The utility involves identifying a physiological parameter potentially related to an onset of patient blindness, monitoring the identified physiological parameter during a medical procedure, and, based on monitoring, taking potentially corrective action in the event of an indication related to a potential onset of patient blindness. It will be appreciated that any physiological parameter determined to be relevant to the onset of patient blindness may be monitored in this regard. Parameters that may be relevant in this regard include ocular pressure, perfusion and oxygen saturation. Any one or combination of these parameters may be monitored during the medical procedure. With regard to perfusion and oxygen saturation, the measurement may be in the arterial, capillary or venous phase of blood perfusion of the retina. These measurements can be perfusion or saturation related and will generally involve measurements of different wavelengths. It may be desirable to monitor such a parameter during a variety of medical procedures, including emergency room procedures and surgical procedures, among others. For example, post-operative blindness has been identified as a problem in relation to certain spinal procedures.
In accordance with a still further aspect of the present invention, a utility is provided for use in monitoring ocular pressure during a medical procedure. The utility includes an eye contact; a pressure sensor, supportably associated with the eye contact, for sensing an ocular pressure of the patient; and a monitoring instrument, supportably associated with the pressure sensor, for use in monitoring the ocular pressure of the patient during a surgical procedure and for providing an indication upon detecting a condition potentially related to an onset of blindness. For example, the monitoring instrument may include a MEMS tonometer or the like. The sensor may be supported on an eye contact, for example, in the form of a contact lens. The pressure parameter may be monitored together with ocular perfusion or oxygen saturation to identify a condition of interest. The condition of interest may be identified based on any one of these parameters or any combination thereof.
For a more complete understanding of the present invention and further advantages thereof, reference is now made to the following detailed description taken in conjunction with the drawings in which:
In the following description, the invention is set forth in the context of a patient monitoring system for monitoring certain ocular parameters of a patient. These parameters may be monitored in a variety of contests, including during a medical procedure. Such a system can be used to address the objective of identifying conditions indicative of potential post-procedure blindness so that these conditions can be addressed by the caring physicians. However, it will be appreciated that various aspects of the invention are applicable in other contexts. For example, the ocular parameters may be monitored independent of any separate medical procedure to monitor the patient's eye health or general health. Accordingly, the invention is not limited to the specific embodiments, implementations and contexts described below.
Referring to
The illustrated system 100 further includes a receiver 108. The receiver 108 receives monitoring signals 106 from the patient. The nature of the receiver 108 varies depending on the parameters being monitored and the nature of the monitoring signals 106. Thus, for example, in the case of optical signals used to monitor retinal perfusion or oxygen saturation, the monitoring signals 106 may be optical signals (e.g., transmitted to the detector system via fiber optics) or may be electrical signals representative of optical signals (e.g., in the event of an upstream photodetector). In the case of a system for monitoring ocular pressure, an electrical signal indicative of ocular pressure may be received at the detector 108. Moreover, the number of interrogation signals 104 transmitted to the patient may differ from the number of monitoring signals 106 received from the patient. For example, in the case of a hybrid system including active and passive parameter monitoring (e.g., active retinal oxygen saturation or ocular perfusion monitoring and passive ocular pressure monitoring), the monitoring signals 106 may include signals corresponding to the interrogation signals 104 as well as signals relating to the passive monitoring. The monitoring signals 106 may be optical, electrical or other signals and, in the case of electrical signals, may be analog or digital signals.
The receiver 108 is operative to provide an output electrical signal 109 to the signal processing unit 110. Thus, in the case of optical monitoring signals 106, the receiver 108 may include a photodetector for receiving the optical signals and providing an associated output signal 109. The signal processing unit 110 processes the signal 109 to provide a processor signal 111 for use by the processor 112. Thus, the signal processing unit 110 may perform a number of functions including signal amplification, digital-to-analog conversion, demodulating or de-multiplexing and other signal conditioning.
Different technologies can be utilized to determine retinal oxygen saturation, with corresponding differences in transmitted and received optical signals, transmitting and receiving optical components and processing components. For example, depending on the implementation, the signal 109 may convey, for example, information corresponding to a pixel based image of the ocular fundus (e.g., of retinal tissue) or may be used to derive an analog value. In the case of a pixel-based image, the photodetector may include a CCD or CMOS imaging photodetector. In the case of deriving an analog value, the photodetector may include a single detector unit for providing a current or voltage signal representative of the light incident thereon.
The processor 112 receives the processor signal 111 and processes the signal 111 so as to enable substantially real-time patient monitoring. The illustrated processor 112 includes a parameter calculation module(s) 114, a monitoring module 116 and an output module 118. The parameter calculation module 114 calculates at least one physiological parameter believed to relate to post-operative blindness in the illustrated embodiment. For example, the parameter may be related to ocular perfusion, retinal oxygen saturation or ocular pressure (or changes in derivative/related values of any of the above). Thus, in the case of ocular pressure, the input signal 111 may be analyzed to determine a value related to ocular pressure or change in ocular pressure. Similarly, in the cases of retinal oxygen saturation or perfusion, a value related to these parameters or changes in these parameters may be calculated.
An image subtraction algorithm may be used in regard to oxygen saturation or perfusion measurements. Generally, these algorithms involve obtaining a first image at a first wavelength of transmitted light, obtaining a second image at a second wavelength, and digitally subtracting one image from the other to obtain a differential image. The differential image includes information that is correlated to the perfusion and oxygen saturation of the tissue under examination. The images can be processed to identify the optic nerve or other location of interest (e.g., the macula) for performing the perfusion or oxygen saturation analysis. Processing techniques specific to retinal oxygen saturation determinations may be used in this regard. Relevant technology in this regard is disclosed in the following references, which are incorporated herein by reference: Denninghoff, et al., Retinal venous oxygen saturation and cardiac output during controlled hemorrhage and resuscitation, Journal of Applied Physiology 94: 891-896, 2003; de Kock, et al., Reflectance Pulse Oximetry Measurements from the Retinal Fundus, IEEE Transactions on Biomedical Engineering, Vol. 40, No. 8, August 1993; and Khoobehi, et al., Hyperspectral Imaging for Measurement of Oxygen Saturation in the Optic Nerve Head, Investigative Ophthalmology & Visual Science, Vol. 45, No. 5, May 2004.
The monitoring module 116 is operative to use the calculated physiological parameter to identify a condition of interest. For example, an ocular pressure value, ocular perfusion value or oxygen saturation value (or changes therein) may be compared to a threshold to identify the condition of interest. In this regard, an ocular pressure above a certain threshold or above a threshold for a certain period of time may indicate a condition of interest. Similarly, an increase in ocular pressure over a given time interval may indicate a condition of interest. With regard to oxygen saturation, an oxygen saturation value dropping below a threshold value (e.g., below 70%) or below a threshold value for a certain length of time may indicate a condition of interest. Alternatively, a change in oxygen saturation, e.g., a drop of more than 20% over a given time period, may indicate a condition of interest. In any of these cases, the threshold values may be determined on a patient-by-patient basis, for example, in relation to a baseline value determined for the patient prior to initiation of the surgical procedure. The specific values used to determine the existence of a condition of interest may be determined theoretically or empirically. The values may balance the need to timely identify a condition of interest versus the annoyance and potential danger of false positives. Moreover, the values may be adjustable to allow specific physicians or institutions to select thresholds as desired. The data may be monitored continuously or frequently during a procedure entailing a high risk to the patient of visual loss.
The illustrated processor 112 further includes an output module 118 for providing output information that may be monitored by a physician or other personnel. For example, the output module 118 may output information continuously or, alternatively, only in the event of a condition of interest. In the latter case, the output module may output audio, visual or other alarms in the case of a condition of interest. In the case of continuous output, the output module 118 may output parameter values, such as instantaneous pressure or oxygen saturation values or a plot of such values over time. Additionally, the output module 118 may output a waveform reflecting such values over time or other information in the case of retinal oxygen saturation implementations.
The connector boxes 210 may simply connect the contact connectors 208 to the instrument connectors 212. Alternatively, some processing may be implemented at the boxes 210. For example, the boxes 210 may include photodetectors such as cameras. In such a case, the connectors 208 may be fiber optic connectors whereas the connectors 212 may be electrical cables. The instrument connectors 212 connect to the processing module 204 at input ports 214. The connectors 212 may be detachably or permanently connected in this regard. The illustrated processing module further includes a display 216 and an on/off switch 206. The on/off switch allows the processing module 204 to be selectively enabled or disabled during medical procedures or otherwise as desired. The display 216 can provide parameter values and/or alarms or warnings in the case of conditions of interest.
The mounting system 302 includes a contact lens 310 for placement on the patient's eye 308. Receptors 312 are mounted on the contact lens 310 and are dimensioned to receive the input and output optical pathways 304. The optical pathways 304 and 306 may be held in the receptors 312, for example, by a friction fit or by way of an adhesive or by way of a mechanical latching system or band that serves to trap and/or strain relieve the optical pathways 304 and 306. The ends of the optical pathways 304 and 306 may butt against the contact lens 310 or may be spaced therefrom. In this regard, an adhesive may be used to bond the ends of the optical pathways 304 and 306 to the surface of the contact lens 310. For optimal performance, the adhesive may be selected for transparency at the operating wavelengths and may be index matched to the optical pathways 304 and 306 and/or contact lens 310 for improved optical transmission. In addition, a clear gel may be used between the contact lens 310 and the patient's eye to cushion the eye and provide for enhanced optical transmission. The patient may be medicated or otherwise treated to inhibit eye movement during the procedure.
In operation, the input pathway 304 may be connected to one or more optical sources. For example, the sources may be operated to sequentially transmit light at multiple frequencies within the frequency range of 400-1000 nm so as to obtain multiple images. The output pathway 306 may be optically coupled to a CCD or CMOS camera or other optical detector. Although a single input pathway 304 and a single output pathway 306 are shown, it will be appreciated that multiple input and/or multiple output pathways may be used. As a further alternative, a single optical pathway may be used for the input and output optical signals. Moreover, each of the illustrated optical pathways may comprise a fiber optic bundle including numerous optical fibers. The bundle is preferably a coherent optical imaging bundle and is flexible and of low mass so as not to put excessive torque on the eye or contact lens.
As noted above, it may be desired to optically couple the input optical pathway to multiple optical sources, e.g., for providing light at multiple frequencies. The multiple sources may be coupled to the input optical pathway in a variety of ways.
The other ends of the pigtails 327-330 are optically coupled to the input optical pathway 326. In the illustrated embodiment, this is accomplished by butt coupling the ends of the pigtails 327-330 to the end of the input optical pathway 326. An optical adhesive may be used to maintain this coupling. Alternatively, a bracket, together with optics or optical adhesives, may be used to couple the pigtails 327-330 to the input optical pathway 326.
Alternatively, the sources may be coupled to the input optical pathway by way of a free space interface. An embodiment of such a free space interface 340 is shown in
The illustrated optical board 602 includes an optical transmission system 608 and an optical detection system 606. The optical transmission system 608 is operative to transmit optical signals into an input fiber 609 for transmission to one or both of the patient's eyes. As best shown in
In the illustrated embodiment, the optical beams from the sources 615 and 616 are both transmitted to the patient's eye via a common input fiber 609. This is accomplished in the illustrated embodiment by way of the dichroic beam combiner cube 617. The cube 617 is formed in two halves with an optical coating at the interface therebetween. The coating is substantially transparent to the beam transmitted by source 615 but is effective to redirect beams transmitted by the source 616 such that beams from the sources 615 and 616 exit the beam combiner 617 coaxially. The input fiber 609 terminates a ferrule that is mounted on the optical board 602. The beams exiting the beam combiner 617 are admitted into the input fiber 609 via optics 618, such as a focusing lens. The various components 614-619 are mounted on the optical board 602 by appropriate mounting mechanisms.
The optical detection system, as best shown in
The foregoing description of the present invention has been presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.
This application is a Continuation-In-Part application that claims priority from U.S. application Ser. No. 11/567,597, entitled, “Intra-Operative Ocular Parameter Sensing,” filed Dec. 6, 2006, which claims priority from U.S. Provisional Application No. 60/748,101, entitled: “Intra-Operative Visual Pressure and Perfusion Change Detector,” filed on Dec. 6, 2005, the contents of both of which are incorporated herein as if set forth in full.
| Number | Date | Country | |
|---|---|---|---|
| 60748101 | Dec 2005 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11567597 | Dec 2006 | US |
| Child | 11675178 | Feb 2007 | US |
