US20090213283A1 - Apparatus and method for adjustable variable transmissivity polarized eye glasses - Google Patents

Abstract

Adjustable variable transmissivity (AVT) eyewear for patients, the AVT eyewear having a liquid crystal lens driven by an electronics circuit so that light transmitted through the lens is detected, the transmitted light being driven to a setpoint by the electronics circuit according to feedback control on the liquid crystal lens drive voltage duty cycle. In another embodiment, light detected from the ambient is detected and the resulting photocurrent value processed by a microprocessor included in the electronics circuit, the microprocessor driving the liquid crystal lens to a desired transmissivity, the desired transmissivity given by a computed transmissivity curve. The computed transmissivity curve may be controlled by the physician or in an alternate embodiment controlled by the patient according to a set of electronic controls on the AVT eye glasses.

Description

FIELD OF INVENTION
• 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.
BACKGROUND OF THE INVENTION
• 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/m²to 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.
SUMMARY OF INVENTION
• 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.
BRIEF DESCRIPTION OF DRAWINGS
• 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:
• FIG. 1A is a frontal view of a first embodiment AVT eye glasses showing the lens and frames.
• FIG. 1B is a top view of a first embodiment AVT eye glasses showing the frames and earpieces.
• FIG. 1C is a side view of a first embodiment AVT eye glasses while partially folded.
• FIGS. 1D and 1E are right and left side views, respectively, of a first embodiment AVT eye glasses while unfolded.
• FIG. 2A is a cross-sectional view of a light plug situated in the AVT eyeglasses frame.
• FIG. 2B is a perspective view of a light plug.
• FIG. 2C is a frontal view of the light plug situated in the eyeglasses frame.
• FIG. 2D is a cross-sectional view of a light pipe plug situated in the AVT eye glasses frame.
• FIG. 2E is a perspective view of a light pipe plug.
• FIG. 3A is a frontal view of the of second embodiment AVT eye glasses showing the frames and light sensor position behind the lens.
• FIG. 3B is a top view of the of second embodiment AVT eye glasses showing the frames and light sensor position behind the lens.
• FIG. 3C is a side view of the second embodiment AVT eye glasses.
• FIG. 3D is a cross-sectional view of a light pipe plug situated behind the AVT eye glasses lens.
• FIG. 4 is a geometric drawing of the lens structure in the preferred embodiment of the present invention.
• FIG. 5A is a front perspective drawing of the inner and outer lens substrates with top down view looking towards the front face of the lenses, the drawing pertaining to the fail dark lens substrate arrangement.
• FIG. 5B is a front perspective drawing of the inner and outer lens substrates with top down view looking towards the front face of the lenses, the drawing pertaining to the fail light lens substrate arrangement.
• FIG. 6 is a block diagram of the electronic circuitry for the AVT glasses with direct ambient photosensing.
• FIG. 7 is a block diagram of the electronic circuitry for the AVT glasses with photosensing from behind the lens.
• FIG. 8 is a block diagram of the electronic circuitry for the AVT glasses with direct ambient photosensing and using a microprocessor for control in the preferred embodiment.
• FIG. 9 is a graph of AVT glasses transmittance curves showing the preferred embodiment transmissivity curve.
• FIG. 10 is a graph showing the LCD response curve of transmissivity versus duty cycle in the preferred embodiment of the present invention, curves for fail dark and fail light modes are shown.
• FIG. 11 is pseudocode listing of the modulation software used by the microprocessor to control the function of the eyeglasses and the lenses.
• FIG. 12A is block diagram of an apparatus to calibrate the light sensor of the eyeglasses.
• FIG. 12B is a block diagram of an apparatus to calibrate the transmissivity of the eye glass lenses.
• FIG. 13 is a flow chart of a preferred method to calibrate the AVT eyeglasses.
• FIG. 14 is a flow chart of a physician's program.
• FIG. 15 is a graphical depiction of the display page of the physician's program.
• FIG. 16 is a graph of a typical light sensor response.
• FIG. 17 is a graph of a typical light sensor spectral response.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
• 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.
• FIGS. 1A,1B,1C show the first embodiment frontal view, top view and side view, respectively, of partially closedAVT eyeglasses10 incorporating the present invention.FIG. 1A is a frontal view of AVTeyeglasses10 which includelens12 andlens14 mounted inframe16.Lens12 andlens14 have electronically controllable optical density for controlling the amount of light transmitted to a wearer's eyes. The structure oflens12 and14 is described in detail below.Sensor element30 is integrated into thebridge area26 offrame16 and contains alight sensor32 which in the first embodiment senses ambient light in front ofeyeglasses10. Attached to frame16 by hinges8 and9, areearpieces18 and20, respectively for holding AVT eyeglasses securely on the wearer's head, the earpieces suitably folding for storage.
• Referring toFIGS. 1D and 1E, side views of normally openedAVT eyeglasses10 show that anelectronics circuit33 is integrated intoearpiece20,electronics circuit33 being electrically attached tolight sensor32 and tobatteries22 contained inbattery compartment21.Ear piece18 also has leftcontrol36;ear piece20 also hasright control37, the controls used in the preferred embodiment to set the lower and upper light level limits for electronic control of the duty cycle for maximum and minimum transmission of the light through the lens. An on/off switch may be incorporated intoear pieces18 and20 near hinges8 and9, respectively, such that the switch is turned on when the ear pieces are unfolded for wearing, supplying voltage from the battery toelectronics circuit33. Thecontrols36 and37 are a button type switch in a preferred embodiment. In an alternate embodiment, controls36 and37 may be rotatable screws connected to a potentiometer. Other embodiments include slide switches or other rotating switches as known in the art.
• The placement ofcontrols36 and37 and the on/off switch may be accomplished in a variety of ways in other embodiments consistent with the present invention. For example, controls36 and37 may be incorporated into the ear pieces in another embodiment. In yet another embodiment, controls36 and37 may constructed to make patient control more difficult so that settings are managed by a physician.
• FIGS. 2A,2B and2C show details ofsensor element30 which is comprised of ahole29 inbridge area26 having aclear plug25, anoutput aperture28b, and alight sensor32 fixed behind theoutput aperture28b. Clear plug25 has a clear hole withinner surface35 to which aninput aperture28ais mounted as shown inFIGS. 2B and 2C. The input and output apertures create a field ofview27 from which light is collected ontolight sensor32 which measures the ambient light luminance collected within field ofview27 from the front ofAVT eye glasses10.Output aperture28bmay have its center offset from the center ofinput aperture28a, the offset being in the vertical or horizontal direction by an offsetdistance31. A vertical offsetdistance31 causes a vertical shift of the field of view while a horizontal offsetdistance31 causes a horizontal shift of the field of view. The horizontal plane is defined as the plane containing the center point of both lenses. The vertical plane is a plane perpendicular to the horizontal plane for which all points are equidistant from the center point of both lenses.
• 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 intobridge area26 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.
• FIGS. 2D and 2E show detail of an alternate embodiment of a sensor element,sensor element50 which is comprised of a clear plasticlight pipe55 inserted intohole59 ofbridge area26 havinginput aperture58aon afirst surface61a, anoutput aperture58bon asecond surface61band alight sensor52. The input and output apertures create a field ofview57 so that light is collected ontolight sensor52 which measures ambient light luminance collected within field ofview57 to the front ofAVT eye glasses10.Shoulder62 onlight pipe55 abuts to theeye glass frame16.Input aperture58aandoutput aperture58bmay be formed by depositing metal onsurfaces61aand61band etching the deposited metal to create transparent areas on both surfaces.Output aperture58bmay have its center offset from the center ofinput aperture58a, the offset being in the vertical or horizontal direction by an offset distance (not shown). As withclear plugs25, light pipes with different fields of view and different offset distances may be inserted intobridge area26 as required for the wearer.
• FIGS. 3A,3B,3C show a second embodiment ofAVT eyeglasses11 of the present invention.FIG. 3A is a frontal view of AVTeyeglasses11 which includeslens12 andlens14 mounted inframe16,lens12 andlens14 have electronically controllable optical density as in the first embodiment.Sensor element40 is contained in thebridge area26 offrame16 and has alight sensor42.Light sensor42 is positioned behindlens12 so that it senses light that is transmitted throughlens12.AVT eyeglasses11 also have earpieces, an electronics circuit, controls and a battery compartment similar to those described forAVT eyeglasses10.
• FIG. 3D shows detail ofsensor element40 which is comprised of alight pipe49 havinginput aperture48aandoutput aperture48b, a mountingassembly41 and alight sensor42. The input and output apertures create a field ofview47 from which light is collected ontolight sensor42 which measures the luminance of light collected within field ofview47 and transmitted throughlens12 to the front ofAVT eye glasses10.Input aperture48aandoutput aperture48bare integrated intolight pipe49,input aperture48abeing adjacent to the rear surface oflens12. As before,input aperture48amay be offset fromoutput aperture48bto move the field of view vertically or horizontally.
• FIGS. 4,5A and5B show the structure ofLCD lens100 of the present invention. InFIG. 4,lens100 corresponds tolens12 andlens14 ofFIGS. 1-3.Lens100 is comprised of a twisted nematicliquid crystal material110 sandwiched between aninner substrate101 nearest the wearer'seye103 and anouter substrate102 nearest the object orlight source105. The incident light hasdirection vector117 and the transmitted light hasdirection vector109. Theouter substrate102 is comprised of several layers and components. Starting from the front surface and moving towards theeye103, an input polarizingthin film104 is coated onto a first electrically conductiveITO glass substrate106, the rear facing surface being coated with a first layer of Indium Tin Oxide (ITO)107 upon which is a first thin filmpolyimide alignment layer108 which is scribed in a first direction. The firstpolyimide alignment layer108 is in contact with liquidcrystalline material110. A second thin filmpolyimide alignment layer112 is coated onto to asecond ITO layer113 on the front facing surface ofglass substrate114 and scribed in a second direction. The rear facing surface ofglass substrate114 is coated with an output polarizingthin film116. As is known in the art, an electric potential is applied between the first conductingITO glass substrate106 and the second conductingITO glass substrate114 to affect the orientation of the liquid crystal and thereby change the transmissivity of thelens100. In the preferred embodiment, the applied electric potential is an alternating potential.
• 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.
• FIG. 5A shows a fail dark embodiment of thelens100 so that when the electric potential is zero betweeninner substrate101 andouter substrate102, thelens100 has a low transmissivity. TheFIG. 5A is drawn so that the surfaces while looking down at the page are the front facing surfaces of the two lens substrates looking towards the wearer's eye; a further description being that the transmittedlight vector109 is going into the page inFIG. 5A. In the preferred embodiment, the fail dark transmissivity value is approximately 6%. In other embodiments the fail dark transmissivity may achieve a lower value. In the fail dark configuration, the polarizer ofouter substrate102 is arranged to transmit linear polarization infirst direction131 and alignment layer scribed insecond direction132, thefirst direction131 being vertical and thesecond direction132 being at an angle of 45 degrees clockwise from horizontal. Furthermore, the polarizer ofinner substrate101 is arranged to transmit linear polarization inthird direction133 and alignment layer scribed infourth direction134, thethird direction133 being vertical and thefourth direction134 being 45 degrees counterclockwise from horizontal.
• FIG. 5B shows a fail light embodiment of thelens100 wherein when the electric potential is zero betweeninner substrate101 andouter substrate102, thelens100 has a high transmissivity.FIG. 5B is drawn similar toFIG. 5A so that the transmittedlight vector109 is going into the page. In the alternate embodiment, the fail light transmissivity value is approximately 30%. In other embodiments, the fail light transmissivity may be higher. In the fail light configuration the polarizer ofouter substrate102 is arranged to transmit linear polarization infifth direction151 and alignment layer scribed insixth direction152, thefifth direction151 being vertical and thesixth direction152 being 45 degrees clockwise from the horizontal direction. Furthermore, the polarizer ofinner substrate101 is arranged to transmit linear polarization inseventh direction153 and alignment layer scribed ineighth direction154, theseventh direction153 being horizontal and the eightdirection154 being 45 degrees counterclockwise from the horizontal direction.
• FIG. 6 is a block diagram of a first embodimentelectronic circuit200.Electronic circuit200 provides electronic control of the transmissivity oflens element218 allowing for a certain fraction of incident light201 to fall on a wearer'seye219 and is comprised of a dc/dc boost converter221 connected to abattery220; alight sensor202; anamplifier204 connected tolight sensor202, theamplifier204 havinggain control205 andbias control206; apulse width modulator210 connected toamplifier204; anoscillator211 driving the frequency and timing of thepulse width modulator210; abuffer amplifier214 connected tolens element218 for conditioning adrive signal216 to drivelens element218, the input ofbuffer amplifier214 connected topulse width modulator210 and generatingPWM signal212.Incident light201 which is directly from the ambient, falls onlight sensor202 where the detected light quanta are converted to aphotocurrent203.Photocurrent203 is sensed byamplifier204 and converted to aphotovoltage208. The gain betweenphotovoltage208 andphotocurrent203 is set bygain control205 and a voltage offset being set bybias control206. In the preferred embodiment,gain control205 andbias control206 are factory set. Thephotovoltage208 determines the duty cycle of thePWM signal212. In this exemplary embodiment,PWM210 is a 555 timer chip operating in PWM mode as known in the art, withphotovoltage208 driving the 555 timer's control voltage input.Amplifiers204 and214 may be in inverting or non-inverting types so as to generate an appropriate PWM control voltage for a fail light mode of operation or a fail dark mode of operation, respectively. The duty cycle varies from about 5% to about 50%.
• FIG. 7 is a block diagram of a second embodimentelectronic circuit240.Electronic circuit240 provides electronic control of the transmissivity of lens element242 allowing for a certain fraction of incident light241 to fall on a wearer'seye243 and is comprised of alight sensor244 generatingphotocurrent234; an integratingtransimpedance amplifier245 connected tolight sensor244 havingsensitivity control246 and anoutput photovoltage signal235 proportional tophotocurrent234.Electronic circuit240 further comprises acomparator247 withvoltage reference253; acharging circuit250 connected to capacitor251 for charging a capacitor251 havingpeak voltage reference248, avoltage follower254 connected to capacitor251 and chargingcircuit250; a pulsewidth modulator circuit256 connected to the output ofvoltage follower254 and driven by anoscillator255, and abuffer amplifier258 connected toPWM circuit256 and to lens element242 for driving lens element242.PWM circuit256 produces aPWM signal259 of variable duty cycle and fixed period, the period being determined byoscillator255.
• Photovoltage signal235 is connected to the input ofcomparator247 which enables charging signal237aor dischargingsignal237bdepending upon a comparison between thephotovoltage signal235 and thereference voltage253. If the photovoltage signal is less than the reference voltage, then thecharge signal237ais enabled and chargingcircuit250 allows capacitor251 to be charged to acapacitor voltage252 determined bypeak voltage reference248. If the photovoltage signal is greater than the reference voltage, then thedischarge signal237bis enabled and chargingcircuit250 discharges capacitor251 causing thecapacitor voltage252 to go to ground. If the photovoltage signal is approximately the same as the reference voltage, then neither ofsignals237aor237bare enabled and thecapacitor voltage252 is not altered except for circuit leakages.
• Avoltage follower254 creates current bufferedPWM input voltage238 proportional tocapacitor voltage252,PWM input voltage238 determining the duty cycle ofPWM signal259.PWM circuit256 is connected to bufferamplifier258, which in turn drives the lens element.PWM circuit256 may be a 555 timer chip operating in PWM mode as known in the art, withPWM input voltage238 driving the 555 timer's control voltage input. The duty cycle varies from about 5% to about 50%.
• FIG. 8 is a block diagram of a third embodimentelectronic circuit260.Electronic circuit260 provides electronic control of the transmissivity oflens element282 allowing for a certain fraction of incident light262 to fall on a wearer'seye280 and is comprised of a DC/DC converter265 connected tobattery266 and having outputDC voltage Vcc259 for powering the components ofcircuit260; a light sensor261 forsensing incident light262; acrystal oscillator267 oscillating at frequency f1; asquare wave oscillator283 oscillating at frequency f2 producingsquare wave signal287 connected to amicroprocessor268 and an ANDgate284;microprocessor268 having an A/D converter264 connected to light sensor261 and atimer263 connected tocrystal oscillator267,microprocessor268 further havingmemory269 which containsprogram instructions285 for operation and for generating a pulse width modulated signal; and aserial interface271 for communications withmicroprocessor268.
• Electronic circuit260 also has acharge pump circuit279 for generating an alternating current drive signal and further contains an ANDgate284 with one input beingsquare wave signal287 and a second input beingGATE line272 which is connected to and driven bymicroprocessor268. The output of ANDgate284 isPWM signal273 which is connected to chargepump circuit279.
• Charge pump circuit279 is comprised of anon-inverting buffer270aand invertingbuffer270b, a set ofpolarized capacitors275aand275b; a set ofresistors276aand276b; and a set ofdiodes277aand277b. Both buffers having their inputs tied to PWM signal273.Capacitor275ahas its negative side connected to thenon-inverting output274aofbuffer270aand its positive side connected to the cathode ofdiode277a, to first end ofresistor276aand tooutput line278a. The anode ofdiode277aand the second end ofresistor276aare tied to ground.Capacitor275bhas its positive side connected to the invertingoutput274bofbuffer270band its negative side connected to the anode ofdiode277b, to a first end ofresistor276band tooutput line278b. The cathode ofdiode277band the second end ofresistor276bare tied to ground. The voltage acrossoutput lines278aand278balternates between zero and twice Vcc.
• In another embodiment ofelectronic circuit260, the AND gate may be synthesized in the program logic contained in program instructions and theGATE line272 becomes equivalent to PWM signal273.
• In operation, incident light262 falls on light sensor261 wherein the detected light quanta are converted to photocurrent and then to a photovoltage proportional thereto. The photovoltage is read by A/D converter264 in conjunction withmicroprocessor268 to determine a measured incident light luminance which is used according toprogram instructions285 to driveGATE line272 which sets the duty cycle ofPWM signal273. Besidesprogram instructions285,microprocessor268 has stored inmemory269parameters286 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 thatelectronic circuit260 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 instructions285 will be described according to the discussion ofFIG. 10 below.
• Microprocessor268 hasserial interface271 for downloadingprogram instructions285 andparameters286.Serial interface271 may be wired or it may be wireless as in a Bluetooth transmitter and receiver. In the preferred embodiment,serial interface271 is of type I²C andmicroprocessor268 is the MP430 ultra low power MCU available from Texas Instruments, Inc.
• Third embodimentelectronic circuit260 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 circuit260 may be operated in a direct view mode or in a transmitted light mode. In the transmitted light mode consistent with secondembodiment AVT eyeglasses11,microprocessor268 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 firstembodiment AVT eyeglasses10,microprocessor268 is programmed to produce a lens transmissivity for a given input light level.
• FIG. 9 is a graph of atypical transmittance function295 employed for direct view modeAVT eye glasses10. The abscissa is the ambient luminance measured in cd/m²(L_in) and the ordinate is the transmissivity throughlenses12 and14, the transmissivity being the fraction of light transmitted through the lens. Thetransmittance function295 is typical of a fail dark mode of operation and is comprised of three regions, the controlledregion290, the fullypowered transmittance region291, and the powered offtransmittance region292. The fullypowered transmittance region291 transitions to the controlledregion290 at an ambient luminance of L1 corresponding to point293 on the transmittance curve. The controlledregion290 transitions to the powered offtransmittance region292 at luminance L2 corresponding to point294 on the transmittance curve.
• In the preferred embodiment, the transmittance function for the controlledregion290 takes the form of the Weber Fechner law which is logarithmic in response.Transmittance function295 is summarized according to the formula:
• $T=\left\{\begin{array}{cc}{T}_{\max }& L_i\le L_1\\ a\log L_i+\mathrm{<figure-callout\; label="b\; L"\; filenames="US20090213283A1-20090827-D00009.png,US20090213283A1-20090827-D00010.png"\; state="\{\{state\}\}">b</figure-callout>}& L_{}{}_1<L_i<L_2\\ T_{\min }& L_i\ge L_2\end{array}\right\},$
• wherein T*Li is the transmitted light level (luminance on the eye), L_iis the ambient light level (luminance on the lens), T_maxis the maximum transmittance of thelenses12 and14, T_minis the minimum transmittance of thelenses12 and14, and the coefficients a and b are fit according to
• $a=\frac{T_{\min }L_2-T_{\mathrm{<figure-callout\; label="max\; \; L"\; filenames="US20090213283A1-20090827-D00009.png,US20090213283A1-20090827-D00010.png"\; state="\{\{state\}\}">max</figure-callout>}}L_{}{}_1}{\log L_2-\log {\mathrm{<figure-callout\; label="L"\; filenames="US20090213283A1-20090827-D00009.png,US20090213283A1-20090827-D00010.png"\; state="\{\{state\}\}">L</figure-callout>}}_1},b=T_{\max }L_1-a\log {\mathrm{<figure-callout\; label="L"\; filenames="US20090213283A1-20090827-D00009.png,US20090213283A1-20090827-D00010.png"\; state="\{\{state\}\}">L</figure-callout>}}_1.$
• 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 ofFIG. 10 shows two exemplary LCD response curves, a fail lightmode response curve500 and a fail darkmode response curve501, both curves having duty cycle as theabscissa503 and transmittance T as theordinate502. For a given lens assembly, the transmittance will take on a fixed maximum and a fixed minimum. In the fail light case according tocurve500,maximum transmittance point504, occurs for small duty cycle and aminimum transmittance point505, occurs near the point of maximum duty cycle, the maximum duty cycle being 50% in the exemplary embodiment. In the fail dark case according tocurve501,maximum transmittance point508, occurs near the maximum duty cycle andminimum transmittance point509, occurs for small duty cycle. An AVT lens system operating in fail light mode will have maximum transmittance and maximum light on a wearer's eye when the voltage across the lens goes to zero. An AVT lens system operating in fail dark mode will have minimum transmittance and minimum light on a wearer's eye when the voltage across the lens goes to zero. The preferred mode of operation is to fail dark for the present invention, but either mode may be used.
• In practice, the faildark curve501 is used to compute a required duty cycle for a given transmittance. To simplify and speed up the computation, the faildark curve501 is approximated by three linear functions separated bytransition points506 and507, the firstlinear function510 being defined betweenpoint509 andtransition point506, the secondlinear function511 being defined betweentransition point506 andtransition point507, and the thirdlinear function512 being defined betweentransition point507 andpoint508. In the preferred embodiment, thetransition point506 occurs at about 6% duty cycle and 5.5% transmissivity; thetransition point506 occurs at about 16% duty cycle and 27.5% transmissivity. The transition points and linear fit parameters are typically stored inmemory269 within the set ofparameters286.
• A sensor response curve relating incident light level Li to measured photocurrent of the light sensor is required. A typicalsensor response curve800 is shown inFIG. 16. In practice, sensor response is approximately linear and the slope ofsensor response curve800 is typically stored inmemory269 as one of the set ofparameters286.
• A useful feature ofAVT eye glasses10 is that the spectral response of the sensor approximate the response of the human eye.FIG. 17 showsgraph810 of a typical spectral response, thespectral response curve820 being reasonably close to the response of thehuman eye830. In the preferred embodiment using direct detection of ambient light, thelight sensors202,244, and261 are part APDS-9003 from Avago Technologies Corporation and the graphs ofFIGS. 16 and 17 are taken from the corresponding data sheet.
• Referring again toFIGS. 9 and 10 in operation, the desired transmittance T is computed from the overalltransmittance response function295 for a given ambient light level Li and then the duty cycle D for the desired transmittance T is derived fromLCD response curve500 to control the transmissivity oflenses12 and14. For ambient illumination less than L1 falling on theAVT eye glasses10,lenses12 and14 are turned off transmitting light at a constant maximum lens transmittance, T_max. For ambient illumination greater than L2 falling on theAVT eye glasses10,lens12 and14 operate at their minimum transmittance, T_min, the lens control generally being limited by duty cycle or by polarization efficiency of the inner and outer lens substrates.
• A useful feature of the present invention is the ability of the wearer to set thepoint293 and thepoint294 of thetransmittance curve295, although the AVT eyeglasses are typically set by a trained ophthalmologist in the clinic using a computer interfaced to the eyeglasses.Point293 may be adjusted by pressing and holding theleft control36 momentarily in the preferred embodiment wherein the wearer may accomplish setting the light level L1 to the current ambient light level.Point293 is then (L1, Tmax*L1).Point294 may be adjusted by pressing and holding theright button37 momentarily in the preferred embodiment, wherein the wearer may accomplish setting the light level L2 to the current ambient light level.Point294 is then (L2, Tmin*L2). Whenpoint294 is changed, the extent and the slope of the controlledregion290 of the transmittance curve are adjusted to a new extent and a new slope. For example, prior to adjustment thepoint294 may be (4000, 240); after adjustment thepoint294 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 andright controls36 and37 are pressed and held simultaneously,AVT eye glasses10 resets to default values forpoints293 and294. Other embodiments may be envisioned wherein the setting ofpoints293 and294 is physically accomplished by other means, the present invention not being limited to left and right controls to setpoints293 and294.
• FIG. 11 is a pseudocode listing of acontrol program300 executed bymicroprocessor268 asprogram instructions285 and controlling the various functions of AVT glasses.FIGS. 8,9 and10 are also useful to understanding the operation ofcontrol program300.Control program300 has a first hardware interruptprocedure302, a second hardware interruptprocedure315, a software interruptprocedure306 executed at microprocessor boot up, a “Run”procedure308 which executes the main loop of the program, and threesubroutines320,325 and327 which perform computational functions as explained below. A/D converter264 is read to measure photodetector voltage referred to as photovoltage below. Timer1 is theinternal timer263 ofmicroprocessor268.
• Microprocessor268 can monitor and respond to hardware interrupts, redirecting program flow accordingly. First hardware interruptprocedure302 is triggered by an interrupt created by attempted communications onserial interface271. Code associated with hardware interruptprocedure302 allows parameters to be entered externally and stored inmemory269. Incontrol program300, 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 interruptprocedure315 is triggered by an interrupt created when one ofcontrols36 and37 is pressed and held for a predetermined time. First interruptservice316 associated to theleft control36 measures the photovoltage at the time of the interrupt and sets the variable L1 to the ambient luminance corresponding to the measured photovoltage. Second interruptservice317 associated to theright control37 measures the photovoltage at the time of the interrupt and sets the variable L2 to the ambient luminance corresponding to the measured photovoltage. The interruptprocedure315 also services the situation wherein both the left and right buttons are pressed simultaneously in third service interrupt318 which sets L1 and L2 to default values, the default values having been stored in the set ofparameters286. In an alternate embodiment L1 and L2 refer directly to photovoltage generated from light sensor261 without converting to luminance.
• Software interruptprocedure306 occurs shortly after the electronics are powered, software interruptprocedure306 functioning to initialize the hardware and the variables required for the remainder ofcontrol program300. The variables are initialized according to values stored inmemory269 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, theGate line272 is set to 0 (zero) V and timer1 is reset to zero count. When the initialization is complete the software interruptprocedure306 begins to run “Run”procedure308.
• Theprogram300 generates PWM signal273 according to “Run”procedure308 whereinGATE line272 is made to go high for a time proportional to count2 and made to go low for the remainder of the period ofsquare wave signal287. “Run”procedure308 continuously executes a loop labeledloop1 inFIG. 11 until the eye glasses are powered off or a hardware interrupt occurs.
• 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 ofsquare wave signal287 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 callingsubroutine320 after which the required duty cycle of PWM signal273 to obtain transmissivity T is calculated by callingsubroutine325. Once the duty cycle DC is calculated, count2 is computed as count2=DC*beta, count2 determining the positive pulse width inPWM signal273. Thecontrol program300 limits the slew rate of PWM signal273 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 subroutine320 returns transmissivity T according totransmittance curve295 ofFIG. 9 wherein T=T_max if L_in is less than L1, T=T_min if L_in is greater than L2, otherwise T is given by the transmissivity function
• 
  T=a*log(L_in)+b.
• The slope and the intercept b are computed byCoefficients subroutine327 which fits the transmissivity function to the points (L1, T_max) and (L2, T_min).
• DutyCycle subroutine325 returns a computed duty cycle value D for a given transmissivity T.Duty cycle subroutine325 uses the linear fit parameters associated tolinear functions510,511 and512 described according to the LCD response graph ofFIG. 10. T1 and T2 are the transmissivities atpoints506 and507 of the LCD response graph. D_min is the minimum duty cycle allowed and D_max is the maximum duty cycle allowed, having typical values of 5% and 50%, respectively. For T<T1, D is that the maximum of the value given by thelinear function510 or D_min; for T>T2, D is the minimum of the value given by thelinear function512 or D_max; otherwise D is the value given by thelinear function511.
• Calibration ofeyeglasses10 is accomplished according to apparatus configurations shown inFIGS. 12A and 12B and according to the method shown inFIG. 13. The calibration method is suitable for eyeglasses using the digitalelectronic circuit260 or similar. Similar calibration methods are conceived for the analogelectronic circuits200 and240.
• InFIG. 12A a first calibration configuration650 for measuring light sensor response is shown. Acomputer651 has aninterface654 to a calibratedlight source652, theinterface654 allowing for automatic programming of the luminant intensity oflight source652.Light source652 is typically a diffuse source similar to Model RS-5 light source from Gamma Scientific corporation.Lenses657 held withineyeglasses658 are positioned to face the light source. Aserial interface653 is connected betweencomputer651 andeyeglasses658 for reporting photovoltages measured by the light sensor of the eyeglasses. The light source may be moved laterally so that the field ofview655 of the light sensor on the eyeglasses may be determined.
• FIG. 12B shows a second calibration configuration660 suitable for calibrating the transmissivity ofeyeglasses658.Computer651 has aninterface654 to calibratedlight source652, theinterface654 allowing for automatic programming of the luminant intensity oflight source652. Thelenses657 held withineyeglasses658 are positioned to face the light source. Aserial interface653 is connected betweencomputer651 and the eyeglasses for programming the duty cycle of the PWM drive voltage forlenses657 therein. A calibratedphotodetector665 is placed behind the eyeglass lens facing the calibratedlight source652 and made to detect light from the light source as transmitted through the lens, calibratedphotodetector665 connected tocomputer651 by acomputer interface666. The computer has a program that can vary the duty cycle oflenses657 and for each duty cycle, download the corresponding measured light intensity from calibratedphotodetector665. The values can be stored according to patient and product number for future reference.
• FIG. 13 is a flowchart of acalibration method600 used in conjunction with the first and second calibration configurations. The method begins in thestep601 wherein the PC calibration program is made to run oncomputer651. The eyeglasses are also connected byinterface653 tocomputer651 instep602, the eyeglasses having theelectronic circuit260 therein. A calibration program is downloaded to the memory of the eyeglasses instep604 using theinterface653. The calibration program contains program instructions to be executed by themicroprocessor268 to measure and communicate the photovoltage V from the eyeglasses light sensor. The calibration program also contains program instructions for accepting instructions viainterface653 to set the duty cycle of PWM signal that is drivinglenses657.
• Instep606,computer651 setslight source652 to a first predetermined intensity L and then instep608microprocessor268 measures first photovoltage V corresponding to the light detected by the eyeglasses.Steps606 and608 are repeated inloop609 for at least second and third predetermined intensities and for second and third measured voltages. Instep610 the slope of measured voltage V versus light intensity L is determined and stored as the eyeglasseslight sensor response613.
• Step611 is performed next, wherein thelight source652 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 movinglight source652, 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 ofview615 is stored incomputer651 for later download to the eyeglasses.
• After the light sensor is calibrated insteps606 through611, the LCD lens is calibrated insteps612 through618. Beginning withstep612,computer651 sets thelight source652 to a predetermined instensity L_i.Computer651 then instep614 sends the eyeglasses a set of duty cycles between 0% and 50%, preferably in steps of 2%. Instep616, the computer measures the transmitted light through the lens.Steps614 and616 are repeated for each duty cycle in the set according toloop621. Transmitted light level L_t is measured by calibratedphotodetector665, the measured values of L_t being communicated tocomputer651. Instep618 the LCD response curve similar to thecurve501 ofFIG. 10 is determined for duty cycle versus transmissivity T, wherein T=L_t/L_i and fit coefficients for three regions of operation are determined forlinear functions510,511 and512. Also, T_max and T_min are determined whereby T_max is the maximum transmissivity T measured and T_min is the minimum transmissivity T measured. The values for T_max, T_min, and the three slopes and intercepts for thelinear function510,511 and512 are stored asLCD response coefficients617. The method does not preclude using more than three regions and more than three linear functions, nor does it preclude fitting a more complex function to the LCD response curve.
• In another embodiment, the set of data points (Tk, Dk), measured inloop621 for a set of k duty cycles, are stored in the eyeglasses as an LCD response lookup table. To utilize the lookup table, theDutyCycle subroutine325 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.
• Instep620 the calibration process concludes whenLCD response coefficients617, field ofview615 andsensor response613 are stored into anoperational program619 which is further downloaded into eyeglasses memory for normal operation.Operational program619 is similar toeyeglasses program300 described previously.
• As shown inFIG. 14,physicians program700 is conceived for use alongsideeyeglasses10, the physicians program being operated on a personal computer normally situated in the physician's office in proximity to the patient for which the eyeglasses are intended for use. The physicians program is initiated instep702 which causes a Microsoft Windows program to operate instep704. The Windows program checks that the eyeglasses are connected to the computer instep708 and that the eyeglasses are running a valid operational program; if not, then a warning that the eyeglasses are not ready is displayed by the computer instep709. If the eyeglasses are connected to the computer and running a valid operational program, then a patient data screen is displayed instep710. The physician then enters the patient data instep714 and a desired lower light level L_min in units of cd/m2 instep716. Thephysicians program700 then checks if the light level is in the proper range, which is typically [0.1, 500] cd/m2. If no value is entered, a default value of 15 cd/m2 is chosen in the preferred embodiment. If outside the proper range, then a prompt to reenter the data is displayed on the computer instep719. If the light level is in range, then the patient data and the light level is downloaded to the eyeglasses instep720 and a message to the effect that the eyeglasses have been successfully programmed is displayed instep722. The physician's program ends atstep725 by exiting the program.
• Instep714, 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.
• FIG. 15 shows a typical physician's computer form display associated to the physician'sprogram700, the display fields being apatient name750,patient street address751,patient city address752,patient state753,patient zip code754, date ofservice755 and theminimum light level760.
• Eye glasses10 along withcircuit260 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 interruptprocedure302 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.

Claims (1)

1. Eye glasses having adjustable variable transmissivity for controlling the amount of light on at least one eye positioned behind said glasses comprising:

A frame capable of holding lenses and having earpieces rotatably attached to either side;

Two lenses fixed into the frame and having transmissivity controllable by a lens voltage signal connected to the lenses;

A photoelectric light sensor integrated into the frame so as to sense ambient light in a field of view to the front of the eye glasses and producing a measured photocurrent in response to the ambient light,

a light plug having at least two apertures positionally arranged to define the field of view for the photoelectric light sensor in a horizontal plane and in a vertical plane, the horizontal plane being the plane containing the center points of the two lenses and the vertical plane being a plane which is perpendicular to the horizontal plane, all points in the vertical plane being equidistant from the center points of the two lenses;

An electronic circuit mechanically attached to the frame and electrically attached to the photoelectric light sensor and the lenses, the electronic circuit capable of converting the measured photocurrent to a PWM signal with a duty cycle proportional to the measured photocurrent, the electronic circuit further converting the PWM signal to the lens voltage signal;

control means for controlling transmissivity response of the lens, the control means being mechanically attached to the frame and electrically attached to the electronic circuit;

a set of batteries for powering the electronic circuit and the lenses, the set of batteries being held in a battery compartment made into the frame;

an on/off switch connecting the set of batteries to the electronic circuit, the on/off switch being integrated into the frame;

the lenses each comprising a first glass substrate, a second glass substrate, and a liquid crystal material sealed therebetween; wherein the first glass substrate comprises a first surface coated with an input polarizing film, a second surface coated with a first metal layer of Indium Tin Oxide, and a first alignment layer coated over the first metal layer; wherein the second glass substrate comprises a third surface coated with an output polarizing film, a fourth surface coated with a second metal layer of Indium Tin Oxide, and a second alignment layer coated over the second metal layer; wherein the first glass substrate and the second glass substrate are oriented so that the first alignment layer faces the second alignment layer; and wherein the lens signal voltage is connected between the first metal layer and the second metal layer.

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