Optic function monitoring process and apparatus

Abstract

A method and apparatus for monitoring optic function is provided. The apparatus and method relies on two principle modes of measuring the function of the optic nerve, namely, monitoring VEPs for neural function, and monitoring at least one additional parameter of optic function such as intraocular pressure, blood flow or location of the eye to provide a multi-variable optic function monitor. The method and apparatus is proposed for the use to diagnose and potentially prevent the incidence of POVL and anaesthesia awareness in patients during medical procedures.

What is claimed is: 
     
         1 . An optic monitor comprising:
 at least one sensor band having an inner surface designed to be securedly attached to at least the outer surface of the eyelid;   at least one optic function sensor positioned on the inner surface of the sensor band, said at least one optic function sensor being designed to stimulate and monitor the function of at least one portion of the eye selected from the group consisting of the optic nerve, the optic chiasm and the optic cortex to produce signals, said signals forming a visual evoked potential, the visual evoked potential being characterized by a waveform, and output an optic function signal; and   at least one data processor in signal communication with the at least one sensor band to collect and process the optic function signal from the at least one sensor such that changes in the waveform of the visual evoked potential over time are monitored for an adverse change in optic function, wherein the processing includes an analysis of at least the temporal interval (TL1) between the onset of stimulation (t 0 ) and the absolute magnitude of the second measured maximum visual evoked potential (EVP2) after stimulation, and at least one aspect of the waveform of EVP2 selected from the group consisting of the vertical distance (P2) between the maximum value of the upslope of EVP2 to the nadir (N3) of the EVP2, the peak first time-derivative of EVP2, the mean slope of EVP2, and combinations thereof and communicating the output signals to a user.   
     
     
         2 . The device of  claim 1 , further including a pressure sensor positioned on the inner surface of the sensor band, said pressure sensor being designed to monitor the intraocular pressure of the eye and output a pressure signal. 
     
     
         3 . The device of  claim 1 , further including a blood flow sensor positioned on the inner surface of the sensor band, said blood flow sensor being designed to monitor one of either retinal or optic blood flow and output a blood flow signal. 
     
     
         4 . The device of  claim 1 , wherein the at least one optic function sensor stimulates the eye by producing a visual evoked potential in at least one of the nasal or temporal halves of the optic nerve. 
     
     
         5 . The device of  claim 4 , wherein the at least one optic function sensor is a light emitting diode. 
     
     
         6 . The device of  claim 2 , wherein the pressure sensor is a tonometer. 
     
     
         7 . The device of  claim 3 , wherein the blood flow sensor is selected from one of either a near-infrared spectrometer or a laser Doppler velocimeter. 
     
     
         8 . The device of  claim 1 , further comprising a location sensor being designed to monitor the placement of said eye in relation to the eye socket and output an eye location signal. 
     
     
         9 . The device of  claim 8 , wherein the location sensor is a pressure transducer. 
     
     
         10 . The device of  claim 1 , further comprising a plurality of preprogrammed thresholds for each of the output signals such that the device gives an automated warning should the preprogrammed thresholds be reached. 
     
     
         11 . The device of  claim 1 , wherein the sensor band is incorporated into an eye-cover. 
     
     
         12 . The device of  claim 1 , wherein the eye-cover is a pair of goggles. 
     
     
         13 . The device of  claim 1 , wherein the stimulating and monitoring the function of the eye further includes positioning at least two sensors and two visual evoked potential stimulators proximate to the eye. 
     
     
         14 . The device of  claim 1 , wherein the adverse change is one of either perioperative vision loss (POVL) or anesthesia awareness. 
     
     
         15 . The device of  claim 1 , wherein the at least one processor produces an evaluation number from the waveform of the VEP, said evaluation number being indicative of at least the level of optic function. 
     
     
         16 . The device of  claim 1 , wherein the at least one processor further includes computing an anesthesia evaluation number from the VEP waveform in accordance with an equation selected from the group consisting of:
 P2/TL1, where P2 is the vertical distance between the maximum value of the upslope of a second and largest maximum visual evoked potential (EVP2) measured by the waveform to the nadir (N3) of the EVP2, and TL1 is the temporal interval between the onset of stimulation (t 0 ) and the absolute magnitude of the second evoked potential (EVP2);   (P2/TL1) n , wherein n is an exponent between 0.333 and 3;   (P2) x /(TL1) y , where P2 is the vertical distance between the maximum value of the upslope of a second and largest maximum visual evoked potential (EVP2) measured by the waveform to the nadir (N3) of the EVP2, and TL1 is the temporal interval between the onset of stimulation (t 0 ) and the absolute magnitude of the EVP2, and wherein x and y are an exponents between 0.333 and 3;   ((P2) x /(TL1) y ) n  where n is an exponent between 0.333 and 3;   ((P2) x /(TL1) y ) n  where n is an exponent between 0.5 and 2;   (δ(EVP2)/δt max )/TL1, where (EVP2) is a second and largest maximum visual evoked potential, δ(EVP2)/δt max  is the peak forward upslope of EVP2, and TL1 is the temporal interval between the onset of stimulation (t 0 ) and the absolute magnitude of EVP2;   (δ(EVP2)/δt max ) x /(TL1) y , where (EVP2) is a second and largest maximum visual evoked potential, δ(EVP2)/δt max  is the peak forward upslope of EVP2, TL1 is the temporal interval between the onset of stimulation (t 0 ) and the absolute magnitude of EVP2, and wherein x and y are an exponents between 0.333 and 3;   ((δ(EVP2)/δt max ) x /(TL1) y ) n  where n is an exponent between 0.333 and 3;   (δ(EVP2)/δt mean )/TL1, where (EVP2) is a second and largest maximum visual evoked potential, δ(EVP2)/δt mean  is the mean slope of EVP2 and P2, and TL1 is the temporal interval between the onset of stimulation (t 0 ) and the absolute magnitude of EVP2, and where P2 is the vertical distance between the maximum value of the upslope of a second and largest maximum visual evoked potential (EVP2) measured by the waveform to the nadir (N3) of the EVP2;   (δ(EVP2)/δt mean ) x /(TL1) y , where (EVP2) is a second and largest maximum visual evoked potential, δ(EVP2)/δt mean  is the mean slope of EVP2 and P2, TL1 is the temporal interval between the onset of stimulation (t 0 ) and the absolute magnitude of EVP2, and wherein x and y are an exponents between 0.333 and 3, and where P2 is the vertical distance between the maximum value of the upslope of a second and largest maximum visual evoked potential (EVP2) measured by the waveform to the nadir (N3) of the EVP2;   (δ(EVP2)/δt mean ) x /(t 1   y /P2 z ) m  in (μV/ms), where (EVP2) is a second and largest maximum visual evoked potential, δ(EVP2)/δt mean  is the quotient of P2 and the temporal interval occurring between the onset of the upslope of EVP2 and P2, t 1  is the absolute magnitude of EVP2, P2 is the vertical distance between the maximum value of the upslope of a second and largest maximum visual evoked potential (EVP2) measured by the waveform to the nadir (N3) of the EVP2, and wherein x and y are an exponents between 0.333 and 3;   ((δ(EVP2)/δt mean ) x /(t 1   y /P2 z ) m ) n  where n is an exponent between 0.333 and 3;   δ(EVP2)/δt max /t 1 /P 2  in (μV/ms), where (EVP2) is a second and largest maximum visual evoked potential, δ(EVP2)/δt max  is the peak forward upslope of EVP2, t 1  is the absolute magnitude of EVP2, and P2 is the vertical distance between the maximum value of the upslope of a second and largest maximum visual evoked potential (EVP2) measured by the waveform to the nadir (N3) of the EVP2;   δ(EVP2)/δt max /t 1 /P2 in (μV/ms), where (EVP2) is a second and largest maximum visual evoked potential, t max  δ(EVP2)/δt max  is the peak forward upslope of EVP2, t 1  is the absolute magnitude of EVP2, P2 is the vertical distance between the maximum value of the upslope of a second and largest maximum visual evoked potential (EVP2) measured by the waveform to the nadir (N3) of the EVP2, and wherein x, y and z are an exponents between 0.333 and 3;   (δ(EVP2)/δt mean ) x /(t 1   y /P2 z ) m  in (μV/ms), where (EVP2) is a second and largest maximum visual evoked potential, δ(EVP2)/δt mean  is the mean slope of EVP2 and P2, t 1  is the absolute magnitude of EVP2, P2 is the vertical distance between the maximum value of the upslope of a second and largest maximum visual evoked potential (EVP2) measured by the waveform to the nadir (N3) of the EVP2, and wherein x, y, z and m are an exponents between 0.333 and 3;   ((δ(EVP2)/δt mean ) x /(t 1   y /P2 z ) m ) n  where n is an exponent between 0.333 and 3;   (δ(EVP2)/δt max ) x /(t 1   y /P2 z ) m  in (μV/ms), where (EVP2) is a second and largest maximum visual evoked potential, δ(EVP2)/δt max  is the peak forward upslope of EVP2, t 1  is the absolute magnitude of EVP2), P2 is the vertical distance between the maximum value of the upslope of a second and largest maximum visual evoked potential (EVP2) measured by the waveform to the nadir (N3) of the EVP2, and wherein x, y, z and m are an exponents between 0.333 and 3; and   ((δ(EVP2)/δt max ) x /(t 1   y /P2 z ) m ) n  where n is an exponent between 0.333 and 3.   
     
     
         17 . The device of  claim 16 , wherein the at least one processor further computes a dimensionless anesthesia evaluation index, obtained by dividing the anesthesia evaluation number by a static control value defined as the value of the anesthesia evaluation number measured at a time before the induction of anesthesia. 
     
     
         18 . The device of  claim 1 , wherein the at least one processor further computes two anesthesia evaluation numbers from the VEP waveform in accordance with the equation, (P2) x /(TL1) y , where P2 is the vertical distance between the maximum value of the upslope of a second and largest maximum visual evoked potential (EVP2) measured by the waveform to the nadir (N3) of the EVP2, and TL1 is the temporal interval between the onset of stimulation (t 0 ) and the absolute magnitude of the EVP2, and wherein x and y are an exponents between 0.333 and 3;
 computing a third anesthesia evaluation number according to the equation ((P2) x /(TL1) y ) n  where n is an exponent between 0.333 and 3; and   further comprising computing a dimensionless anesthesia evaluation index obtained by dividing the third anesthesia evaluation number by a static control value defined as the value of the third anesthesia evaluation number measured at a time before the induction of anesthesia.   
     
     
         19 . The device of  claim 16 , wherein the at least one processor further calibrates the anesthesia evaluation number by measuring the anesthesia evaluation number prior to the administration of an anesthesia.