The present invention relates generally to the field of treatment for age related macular degeneration. More specifically, the invention is a set of eye glasses which electronically dim and brighten according to ambient light conditions.
People with age related macular degeneration (ARMD) and similar diseases affecting the ocular media have long retinal adaptation times leading to poor visual acuity during adaptation. Dark adaptation times may be measured in tens of minutes in typical cases. The lack of visual acuity may cause serious mobility problems in people with ARMD, especially near curbs and steps in bright sunlight. Generally, there are problems in the aged relating to contrast sensitivity in varying lighting conditions leading to vision problems while driving during the night time.
Ophthalmologists have long sought a prescriptive solution wherein the ARMD patient may be fit with light absorbing eye glasses that restrict the amount of light reaching the patient's eyes thereby increasing visual acuity. The eye glasses must adapt to a wide range of lighting conditions ranging from the office environment wherein light luminance levels are typically on the order of 12-18 cd/m2 to a bright sunny day outside, wherein luminance levels may be on the order of 5000 cd/m2. The need for light absorbing eye glasses with a wide dynamic range thus exists. Furthermore, the eye glasses must respond quickly to keep the retinal illumination level near an ideal value so that dark adaptation effects are not impaired and retinal bleaching does not occur. As for contrast sensitivity, polarization arrangements yielding a yellow lens color is advantageous to achieving the greatest contrast sensitivity.
While light absorbing eye glasses exist in the prior art, there are fundamental flaws in the prior art designs. One major flaw is the inability of the ophthalmologist to adjust for the patient to patient variation of dark to bright transmission ranges, and for the patient's overall illumination response. The present invention allows for such control by the ophthalmologist. Secondly, control group studies of subject response to light absorbing eye glasses were made according to Ross and Mancil in “Design and Evaluation of Liquid Crystal (LC) Dark Adapting Eye Glasses for Persons with Low Vision”, Final Report, Project #C776-RA, Atlanta V.A. Rehab Center, March 1997, indicating that subjects preferred to maintain some control over the lens behavior of the light absorbing eye glasses. The present invention allows for limited patient manual override through the use of controls on the ear pieces, one control setting the low light level characteristic of the lens function and the other control setting the upper light level limiting characteristic of the lens function.
Examples of beneficial applications of adjustable variable transmissivity eyewear (AVT) of the present invention are conceived for medical applications, sports applications and occupational applications. For medical use, AVT eyewear is useful in the treatment of retinal pigmentosa, ocular albinism, choroidermia, gyrate atrophy, corneal scarring, cataracts and ureitis. A variety of outdoor sporting activities including fishing, hunting, skiing, golf and baseball may benefit from the present invention. Occupational safety applications are conceived for driving, heavy equipment operation, low light military or police maneuvers, oxyacetylene welding and glassblowing.
Apparatus and methods are described herein which teach the construction and the use of light absorbing adjustable variable transmissivity (AVT) eye glasses. AVT eye glasses comprise a set of frames and a pair of lenses attached to the frames, the set of lenses being made of liquid crystal substrates that change their transmittance upon application of an electric potential. The frames are made to fit a wearer's face over prescription eyewear and to house electronics circuits and batteries for controlling the function of the lenses. Additionally, the frames allow for a light pipe connected to a light sensor to detect ambient light from the direction forward of the wearer with variable field of viewing using light pipe plugs to restrict the angle of view as well as the overall field of view. The frames have earpieces attached to which the electronics substrates may be housed and to which a left control and a right control are fixed, the left and right controls electronically connected to electronics circuits contained on the electronics substrates. In an alternate embodiment, the light pipe is configured to detect transmitted light through the lens to maintain a constant light level to the wearer's eye. In yet another embodiment the electronics substrate may be housed in the frames instead of the earpieces.
The liquid crystal lens is comprised of two substrates fixed together and having a liquid crystal material between them. The substrates are further comprised of an Indium Tin Oxide (ITO) coated glass substrate with a polarizing film on one side and an alignment layer on the other side. A fail dark configuration of the alignment and polarizing layers is taught wherein the polarizers are set vertical and the alignment layers are set at −45 degrees and +45 degrees from the horizontal. The fail dark lens configuration causes the lens transmittance to go to a low value when power is removed from the lenses. A fail light configuration is taught wherein the polarizers are set at a 90 degree angle from each other, one being in the vertical and the second being in the horizontal, the alignment layers being at −45 degrees and +45 degrees to the horizontal, respectively. The fail light lens configuration causes the lens transmittance to go to a high value when power is removed from the lenses. Typical fail dark transmittance is 6% and typical fail light transmittance is 29%.
Electronic circuits are taught to accomplish the lens control under different conditions. In the condition wherein ambient light is sensed, an analog electronics circuit and a digital electronics circuit is taught, the latter including the use of a microprocessor. An analog feedback control circuit is taught for the situation when transmitted light is sensed and it is desired to fix the transmitted light level at a given value. Electronics circuits in the preferred embodiment of the present invention utilize a variable duty cycle of alternating current square wave signal to affect control of the lens average voltage and thereby the lens transmissivity.
In the case of the microprocessor based electronics, methods are taught to automatically adjust the light level according to a desired transmissivity curve. In the preferred embodiment, the desired transmissivity curve is the Weber-Fechner logarithmic response. In other embodiments linear response or other response curves may be utilized in the present invention.
Moreover, methods are taught to utilize controls to affect the transmissivity curve, specifically upper and lower light level set points for the light sensor to control the duty cycle for maximum and minimum transmission of light through the lens.
A software program for controlling the function of variable transmissivity eye glasses is explained taking into account the automatic light level adjustment according to a desired transmissivity curve and taking into account the use of controls.
The disclosed inventions will be described with reference to the accompanying drawings, which show important sample embodiments of the invention and which are incorporated in the specification hereof by reference, wherein:
The numerous innovative teachings of the present application will be described with particular reference to the presently preferred embodiments (by way of example, and not of limitation). The present invention teaches an apparatus and corresponding methodology for making and using adjustable variable transmissivity (AVT) eyeglasses.
Referring to
The placement of controls 36 and 37 and the on/off switch may be accomplished in a variety of ways in other embodiments consistent with the present invention. For example, controls 36 and 37 may be incorporated into the ear pieces in another embodiment. In yet another embodiment, controls 36 and 37 may constructed to make patient control more difficult so that settings are managed by a physician.
Clear plugs with different fields of view and different offset distances will be available to the ophthalmologist to allow for the setting of different fields of view, a suitable clear plug being selected and inserted into bridge area 26 as prescribed for the wearer. The geometry of the input and output apertures may be selected to restrict light gathering capability and to set the field of view, for example the apertures may be elliptical with the major axis oriented horizontally and the minor axis oriented vertically to restrict bright light from the sun or overhead lights. The preferred embodiment horizontal field of view is +/−30 degrees about the vertical plane. The preferred embodiment vertical field of view is +10 degrees upwards and −45 degrees downward from the horizontal plane.
In the exemplary embodiment the polarizing film is preferably made of organic dye in base film (polyvinyl alcohol, or PVA), product number NPF Q-12 from Nitto Denko with transmittance of about 41%, polarizing efficiency of about 89%, hue (NBS-a) of −0.6 and hue (NBS-b) of 1, giving rise to a yellow lens color with no applied voltage and a dark blue lens color with applied alternating voltage. Electrical leads are attached by silver epoxy and the lens substrates are surrounded with an adhesive ring.
Photovoltage signal 235 is connected to the input of comparator 247 which enables charging signal 237a or discharging signal 237b depending upon a comparison between the photovoltage signal 235 and the reference voltage 253. If the photovoltage signal is less than the reference voltage, then the charge signal 237a is enabled and charging circuit 250 allows capacitor 251 to be charged to a capacitor voltage 252 determined by peak voltage reference 248. If the photovoltage signal is greater than the reference voltage, then the discharge signal 237b is enabled and charging circuit 250 discharges capacitor 251 causing the capacitor voltage 252 to go to ground. If the photovoltage signal is approximately the same as the reference voltage, then neither of signals 237a or 237b are enabled and the capacitor voltage 252 is not altered except for circuit leakages.
A voltage follower 254 creates current buffered PWM input voltage 238 proportional to capacitor voltage 252, PWM input voltage 238 determining the duty cycle of PWM signal 259. PWM circuit 256 is connected to buffer amplifier 258, which in turn drives the lens element. PWM circuit 256 may be a 555 timer chip operating in PWM mode as known in the art, with PWM input voltage 238 driving the 555 timer's control voltage input. The duty cycle varies from about 5% to about 50%.
Electronic circuit 260 also has a charge pump circuit 279 for generating an alternating current drive signal and further contains an AND gate 284 with one input being square wave signal 287 and a second input being GATE line 272 which is connected to and driven by microprocessor 268. The output of AND gate 284 is PWM signal 273 which is connected to charge pump circuit 279.
Charge pump circuit 279 is comprised of a non-inverting buffer 270a and inverting buffer 270b, a set of polarized capacitors 275a and 275b; a set of resistors 276a and 276b; and a set of diodes 277a and 277b. Both buffers having their inputs tied to PWM signal 273. Capacitor 275a has its negative side connected to the non-inverting output 274a of buffer 270a and its positive side connected to the cathode of diode 277a, to first end of resistor 276a and to output line 278a. The anode of diode 277a and the second end of resistor 276a are tied to ground. Capacitor 275b has its positive side connected to the inverting output 274b of buffer 270b and its negative side connected to the anode of diode 277b, to a first end of resistor 276b and to output line 278b. The cathode of diode 277b and the second end of resistor 276b are tied to ground. The voltage across output lines 278a and 278b alternates between zero and twice Vcc.
In another embodiment of electronic circuit 260, the AND gate may be synthesized in the program logic contained in program instructions and the GATE line 272 becomes equivalent to PWM signal 273.
In operation, incident light 262 falls on light sensor 261 wherein the detected light quanta are converted to photocurrent and then to a photovoltage proportional thereto. The photovoltage is read by A/D converter 264 in conjunction with microprocessor 268 to determine a measured incident light luminance which is used according to program instructions 285 to drive GATE line 272 which sets the duty cycle of PWM signal 273. Besides program instructions 285, microprocessor 268 has stored in memory 269 parameters 286 including at least an upper transmissivity limit, T_max, a lower transmissivity limit, T_min, and incident light levels L1 and L2, associated to the transmissivity limits. In the preferred embodiment, T_min and T_max are predetermined so that electronic circuit 260 is calibrated during manufacture to produce T_min at about 50% PWM signal duty cycle and T_max at about 5% duty cycle. T_max is typically 29% transmissivity and T_min is typically 6% transmissivity. Program instructions 285 will be described according to the discussion of
Microprocessor 268 has serial interface 271 for downloading program instructions 285 and parameters 286. Serial interface 271 may be wired or it may be wireless as in a Bluetooth transmitter and receiver. In the preferred embodiment, serial interface 271 is of type I2C and microprocessor 268 is the MP430 ultra low power MCU available from Texas Instruments, Inc.
Third embodiment electronic circuit 260 has advantages in several aspects: it is easily programmable on the ophthalmologist's bench with the patient, upgradeable to include new features, and suitable for cost effective manufacturability wherein the upgraded features may include different lens structures with different transfer. Electronic circuit 260 may be operated in a direct view mode or in a transmitted light mode. In the transmitted light mode consistent with second embodiment AVT eyeglasses 11, microprocessor 268 is programmed to keep the transmitted light through the lens constant at a prescribed illumination using PID feedback control algorithms known in the art. The direct view mode consistent with first embodiment AVT eyeglasses 10, microprocessor 268 is programmed to produce a lens transmissivity for a given input light level.
In the preferred embodiment, the transmittance function for the controlled region 290 takes the form of the Weber Fechner law which is logarithmic in response. Transmittance function 295 is summarized according to the formula:
wherein T*Li is the transmitted light level (luminance on the eye), Li is the ambient light level (luminance on the lens), Tmax is the maximum transmittance of the lenses 12 and 14, Tmin is the minimum transmittance of the lenses 12 and 14, and the coefficients a and b are fit according to
The Weber Fechner law is known in the art to most closely approximates a human sensory response function, however, other embodiments are conceived wherein other functions may be used, for example a linear response.
The graph of
In practice, the fail dark curve 501 is used to compute a required duty cycle for a given transmittance. To simplify and speed up the computation, the fail dark curve 501 is approximated by three linear functions separated by transition points 506 and 507, the first linear function 510 being defined between point 509 and transition point 506, the second linear function 511 being defined between transition point 506 and transition point 507, and the third linear function 512 being defined between transition point 507 and point 508. In the preferred embodiment, the transition point 506 occurs at about 6% duty cycle and 5.5% transmissivity; the transition point 506 occurs at about 16% duty cycle and 27.5% transmissivity. The transition points and linear fit parameters are typically stored in memory 269 within the set of parameters 286.
A sensor response curve relating incident light level Li to measured photocurrent of the light sensor is required. A typical sensor response curve 800 is shown in
A useful feature of AVT eye glasses 10 is that the spectral response of the sensor approximate the response of the human eye.
Referring again to
A useful feature of the present invention is the ability of the wearer to set the point 293 and the point 294 of the transmittance curve 295, although the AVT eyeglasses are typically set by a trained ophthalmologist in the clinic using a computer interfaced to the eyeglasses. Point 293 may be adjusted by pressing and holding the left control 36 momentarily in the preferred embodiment wherein the wearer may accomplish setting the light level L1 to the current ambient light level. Point 293 is then (L1, Tmax*L1). Point 294 may be adjusted by pressing and holding the right button 37 momentarily in the preferred embodiment, wherein the wearer may accomplish setting the light level L2 to the current ambient light level. Point 294 is then (L2, Tmin*L2). When point 294 is changed, the extent and the slope of the controlled region 290 of the transmittance curve are adjusted to a new extent and a new slope. For example, prior to adjustment the point 294 may be (4000, 240); after adjustment the point 294 may become (5000, 300). Alternative embodiments may restrict either the L1 or the L2 adjustment by a wearer.
Also in the preferred embodiment, if both the left and right controls 36 and 37 are pressed and held simultaneously, AVT eye glasses 10 resets to default values for points 293 and 294. Other embodiments may be envisioned wherein the setting of points 293 and 294 is physically accomplished by other means, the present invention not being limited to left and right controls to set points 293 and 294.
Microprocessor 268 can monitor and respond to hardware interrupts, redirecting program flow accordingly. First hardware interrupt procedure 302 is triggered by an interrupt created by attempted communications on serial interface 271. Code associated with hardware interrupt procedure 302 allows parameters to be entered externally and stored in memory 269. In control program 300, only one parameter, the minimum ambient light level L_min is entered in units of cd/m̂2, otherwise the default value is selected. In the preferred embodiment the default L_min is in the range of 5 to 40 cd/m̂2 and typically set to 15 cd/m̂2.
A second hardware interrupt procedure 315 is triggered by an interrupt created when one of controls 36 and 37 is pressed and held for a predetermined time. First interrupt service 316 associated to the left control 36 measures the photovoltage at the time of the interrupt and sets the variable L1 to the ambient luminance corresponding to the measured photovoltage. Second interrupt service 317 associated to the right control 37 measures the photovoltage at the time of the interrupt and sets the variable L2 to the ambient luminance corresponding to the measured photovoltage. The interrupt procedure 315 also services the situation wherein both the left and right buttons are pressed simultaneously in third service interrupt 318 which sets L1 and L2 to default values, the default values having been stored in the set of parameters 286. In an alternate embodiment L1 and L2 refer directly to photovoltage generated from light sensor 261 without converting to luminance.
Software interrupt procedure 306 occurs shortly after the electronics are powered, software interrupt procedure 306 functioning to initialize the hardware and the variables required for the remainder of control program 300. The variables are initialized according to values stored in memory 269 and include T_min, T_max, detector response alpha, ratio beta which is the ratio of frequencies f1/f2, duty cycle coefficient gamma, minimum light level L1, maximum light level L2, and linear fit parameters for LCD response: T1, T2, a1, b1, a2, b2, a3, b3, D_min and D_max, and count2 which determines the PWM pulse width. Additionally, the Gate line 272 is set to 0 (zero) V and timer1 is reset to zero count. When the initialization is complete the software interrupt procedure 306 begins to run “Run” procedure 308.
The program 300 generates PWM signal 273 according to “Run” procedure 308 wherein GATE line 272 is made to go high for a time proportional to count2 and made to go low for the remainder of the period of square wave signal 287. “Run” procedure 308 continuously executes a loop labeled loop 1 in
First “if structure” 310 is checked each time loop1 repeats and executes a set of instructions if a transition from a low to high voltage level of square wave signal 287 is detected by the microprocessor. The set of instructions in first “if structure” 310 begin by starting timer1 to counting, then the photovoltage is measured and converted to an ambient light luminance value L_in and the GATE line is then set to Vcc. The transmissivity T is then computed for L_in by calling subroutine 320 after which the required duty cycle of PWM signal 273 to obtain transmissivity T is calculated by calling subroutine 325. Once the duty cycle DC is calculated, count2 is computed as count2=DC*beta, count2 determining the positive pulse width in PWM signal 273. The control program 300 limits the slew rate of PWM signal 273 according to the value of gamma in second “if structure” 311.
“Run” procedure includes third “if structure” 312 which is checked each time loop1 repeats. Third “if structure” 312 compares timer1 with count2. If enough time has elapsed so that timer1 has developed a count greater than count2 then GATE line is set to 0 V and timer1 is reset to zero count.
Transmissivity subroutine 320 returns transmissivity T according to transmittance curve 295 of
T=a*log(L_in)+b.
The slope and the intercept b are computed by Coefficients subroutine 327 which fits the transmissivity function to the points (L1, T_max) and (L2, T_min).
DutyCycle subroutine 325 returns a computed duty cycle value D for a given transmissivity T. Duty cycle subroutine 325 uses the linear fit parameters associated to linear functions 510, 511 and 512 described according to the LCD response graph of
Calibration of eyeglasses 10 is accomplished according to apparatus configurations shown in
In
In step 606, computer 651 sets light source 652 to a first predetermined intensity L and then in step 608 microprocessor 268 measures first photovoltage V corresponding to the light detected by the eyeglasses. Steps 606 and 608 are repeated in loop 609 for at least second and third predetermined intensities and for second and third measured voltages. In step 610 the slope of measured voltage V versus light intensity L is determined and stored as the eyeglasses light sensor response 613.
Step 611 is performed next, wherein the light source 652 is moved horizontally to determine the horizontal field of view of the eyeglasses light sensor and then moved vertically to determine the vertical field of view of the eyeglasses light sensor. While moving light source 652, the photovoltage is measured and reported by the microprocessor and displayed on the computer. Typically, the position of the light source and the measured photovoltage is recorded by hand. The photovoltage falls off with position determining the edges of the field of view which is calculated according to the geometry of the apparatus. The field of view 615 is stored in computer 651 for later download to the eyeglasses.
After the light sensor is calibrated in steps 606 through 611, the LCD lens is calibrated in steps 612 through 618. Beginning with step 612, computer 651 sets the light source 652 to a predetermined instensity L_i. Computer 651 then in step 614 sends the eyeglasses a set of duty cycles between 0% and 50%, preferably in steps of 2%. In step 616, the computer measures the transmitted light through the lens. Steps 614 and 616 are repeated for each duty cycle in the set according to loop 621. Transmitted light level L_t is measured by calibrated photodetector 665, the measured values of L_t being communicated to computer 651. In step 618 the LCD response curve similar to the curve 501 of
In another embodiment, the set of data points (Tk, Dk), measured in loop 621 for a set of k duty cycles, are stored in the eyeglasses as an LCD response lookup table. To utilize the lookup table, the DutyCycle subroutine 325 is replaced with a different subroutine that performs the following steps to look up a duty cycle D0 for a given input transmissivity T0: in the first step, looking up two T values in the lookup table nearest T0 in value, T1 and T2; then, looking up the duty cycles D1 and D2 corresponding to T1 and T2; interpolating between (T1, D1) and (T2, D2) to compute D0; and returning D0 to the calling program.
In step 620 the calibration process concludes when LCD response coefficients 617, field of view 615 and sensor response 613 are stored into an operational program 619 which is further downloaded into eyeglasses memory for normal operation. Operational program 619 is similar to eyeglasses program 300 described previously.
As shown in
In step 714, L_min is preferably the light level where the eyeglasses are set to achieve maximum transmissivity. Alternate embodiments are conceived for capturing different patient requirements. The physician's method may also be applied to eyeglasses with analog electronics wherein L_min is set by a rotatable screw control.
Eye glasses 10 along with circuit 260 are considerably flexible in application due to programmability. Other embodiments may be conceived to take advantage of the programmability as a result. For example, different battery types may be accommodated by extending the program of interrupt procedure 302 to enter a battery type and then the corresponding battery voltage taken into account in computing duty cycles.
The exemplary embodiments described are not intended to limit the present invention application to ARMD treatment, but to serve as a concrete description and useful exemplary application of the inventive concept herein.