US20090213283A1

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

Info

Publication number: US20090213283A1
Application number: US12/072,535
Authority: US
Inventors: Robert G. Burlingame; Ernest Gerald Bylander; Walter Wen; Robin Hines
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-02-27
Filing date: 2008-02-27
Publication date: 2009-08-27
Also published as: US8233102B2; WO2009108753A1; US20090213282A1

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 closed AVT eyeglasses 10 incorporating the present invention. FIG. 1A is a frontal view of AVT eyeglasses 10 which include lens 12 and lens 14 mounted in frame 16. Lens 12 and lens 14 have electronically controllable optical density for controlling the amount of light transmitted to a wearer's eyes. The structure of lens 12 and 14 is described in detail below. Sensor element 30 is integrated into the bridge area 26 of frame 16 and contains a light sensor 32 which in the first embodiment senses ambient light in front of eyeglasses 10. Attached to frame 16 by hinges 8 and 9, are earpieces 18 and 20, respectively for holding AVT eyeglasses securely on the wearer's head, the earpieces suitably folding for storage.
Referring to FIGS. 1D and 1E, side views of normally opened AVT eyeglasses 10 show that an electronics circuit 33 is integrated into earpiece 20, electronics circuit 33 being electrically attached to light sensor 32 and to batteries 22 contained in battery compartment 21. Ear piece 18 also has left control 36; ear piece 20 also has right control 37, 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 into ear pieces 18 and 20 near hinges 8 and 9, respectively, such that the switch is turned on when the ear pieces are unfolded for wearing, supplying voltage from the battery to electronics circuit 33. The controls 36 and 37 are a button type switch in a preferred embodiment. In an alternate embodiment, controls 36 and 37 may be rotatable screws connected to a potentiometer. Other embodiments include slide switches or other rotating switches as known in the art.
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.
FIGS. 2A, 2B and 2C show details of sensor element 30 which is comprised of a hole 29 in bridge area 26 having a clear plug 25, an output aperture 28 b, and a light sensor 32 fixed behind the output aperture 28 b. Clear plug 25 has a clear hole with inner surface 35 to which an input aperture 28 a is mounted as shown in FIGS. 2B and 2C. The input and output apertures create a field of view 27 from which light is collected onto light sensor 32 which measures the ambient light luminance collected within field of view 27 from the front of AVT eye glasses 10. Output aperture 28 b may have its center offset from the center of input aperture 28 a, the offset being in the vertical or horizontal direction by an offset distance 31. A vertical offset distance 31 causes a vertical shift of the field of view while a horizontal offset distance 31 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 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.
FIGS. 2D and 2E show detail of an alternate embodiment of a sensor element, sensor element 50 which is comprised of a clear plastic light pipe 55 inserted into hole 59 of bridge area 26 having input aperture 58 a on a first surface 61 a, an output aperture 58 b on a second surface 61 b and a light sensor 52. The input and output apertures create a field of view 57 so that light is collected onto light sensor 52 which measures ambient light luminance collected within field of view 57 to the front of AVT eye glasses 10. Shoulder 62 on light pipe 55 abuts to the eye glass frame 16. Input aperture 58 a and output aperture 58 b may be formed by depositing metal on surfaces 61 a and 61 b and etching the deposited metal to create transparent areas on both surfaces. Output aperture 58 b may have its center offset from the center of input aperture 58 a, the offset being in the vertical or horizontal direction by an offset distance (not shown). As with clear plugs 25, light pipes with different fields of view and different offset distances may be inserted into bridge area 26 as required for the wearer.
FIGS. 3A, 3B, 3C show a second embodiment of AVT eyeglasses 11 of the present invention. FIG. 3A is a frontal view of AVT eyeglasses 11 which includes lens 12 and lens 14 mounted in frame 16, lens 12 and lens 14 have electronically controllable optical density as in the first embodiment. Sensor element 40 is contained in the bridge area 26 of frame 16 and has a light sensor 42. Light sensor 42 is positioned behind lens 12 so that it senses light that is transmitted through lens 12. AVT eyeglasses 11 also have earpieces, an electronics circuit, controls and a battery compartment similar to those described for AVT eyeglasses 10.
FIG. 3D shows detail of sensor element 40 which is comprised of a light pipe 49 having input aperture 48 a and output aperture 48 b, a mounting assembly 41 and a light sensor 42. The input and output apertures create a field of view 47 from which light is collected onto light sensor 42 which measures the luminance of light collected within field of view 47 and transmitted through lens 12 to the front of AVT eye glasses 10. Input aperture 48 a and output aperture 48 b are integrated into light pipe 49, input aperture 48 a being adjacent to the rear surface of lens 12. As before, input aperture 48 a may be offset from output aperture 48 b to move the field of view vertically or horizontally.
FIGS. 4, 5A and 5B show the structure of LCD lens 100 of the present invention. In FIG. 4, lens 100 corresponds to lens 12 and lens 14 of FIGS. 1-3. Lens 100 is comprised of a twisted nematic liquid crystal material 110 sandwiched between an inner substrate 101 nearest the wearer's eye 103 and an outer substrate 102 nearest the object or light source 105. The incident light has direction vector 117 and the transmitted light has direction vector 109. The outer substrate 102 is comprised of several layers and components. Starting from the front surface and moving towards the eye 103, an input polarizing thin film 104 is coated onto a first electrically conductive ITO glass substrate 106, the rear facing surface being coated with a first layer of Indium Tin Oxide (ITO) 107 upon which is a first thin film polyimide alignment layer 108 which is scribed in a first direction. The first polyimide alignment layer 108 is in contact with liquid crystalline material 110. A second thin film polyimide alignment layer 112 is coated onto to a second ITO layer 113 on the front facing surface of glass substrate 114 and scribed in a second direction. The rear facing surface of glass substrate 114 is coated with an output polarizing thin film 116. As is known in the art, an electric potential is applied between the first conducting ITO glass substrate 106 and the second conducting ITO glass substrate 114 to affect the orientation of the liquid crystal and thereby change the transmissivity of the lens 100. 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 the lens 100 so that when the electric potential is zero between inner substrate 101 and outer substrate 102, the lens 100 has a low transmissivity. The FIG. 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 transmitted light vector 109 is going into the page in FIG. 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 of outer substrate 102 is arranged to transmit linear polarization in first direction 131 and alignment layer scribed in second direction 132, the first direction 131 being vertical and the second direction 132 being at an angle of 45 degrees clockwise from horizontal. Furthermore, the polarizer of inner substrate 101 is arranged to transmit linear polarization in third direction 133 and alignment layer scribed in fourth direction 134, the third direction 133 being vertical and the fourth direction 134 being 45 degrees counterclockwise from horizontal.
FIG. 5B shows a fail light embodiment of the lens 100 wherein when the electric potential is zero between inner substrate 101 and outer substrate 102, the lens 100 has a high transmissivity. FIG. 5B is drawn similar to FIG. 5A so that the transmitted light vector 109 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 of outer substrate 102 is arranged to transmit linear polarization in fifth direction 151 and alignment layer scribed in sixth direction 152, the fifth direction 151 being vertical and the sixth direction 152 being 45 degrees clockwise from the horizontal direction. Furthermore, the polarizer of inner substrate 101 is arranged to transmit linear polarization in seventh direction 153 and alignment layer scribed in eighth direction 154, the seventh direction 153 being horizontal and the eight direction 154 being 45 degrees counterclockwise from the horizontal direction.
FIG. 6 is a block diagram of a first embodiment electronic circuit 200. Electronic circuit 200 provides electronic control of the transmissivity of lens element 218 allowing for a certain fraction of incident light 201 to fall on a wearer's eye 219 and is comprised of a dc/dc boost converter 221 connected to a battery 220; a light sensor 202; an amplifier 204 connected to light sensor 202, the amplifier 204 having gain control 205 and bias control 206; a pulse width modulator 210 connected to amplifier 204; an oscillator 211 driving the frequency and timing of the pulse width modulator 210; a buffer amplifier 214 connected to lens element 218 for conditioning a drive signal 216 to drive lens element 218, the input of buffer amplifier 214 connected to pulse width modulator 210 and generating PWM signal 212. Incident light 201 which is directly from the ambient, falls on light sensor 202 where the detected light quanta are converted to a photocurrent 203. Photocurrent 203 is sensed by amplifier 204 and converted to a photovoltage 208. The gain between photovoltage 208 and photocurrent 203 is set by gain control 205 and a voltage offset being set by bias control 206. In the preferred embodiment, gain control 205 and bias control 206 are factory set. The photovoltage 208 determines the duty cycle of the PWM signal 212. In this exemplary embodiment, PWM 210 is a 555 timer chip operating in PWM mode as known in the art, with photovoltage 208 driving the 555 timer's control voltage input. Amplifiers 204 and 214 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 embodiment electronic circuit 240. Electronic circuit 240 provides electronic control of the transmissivity of lens element 242 allowing for a certain fraction of incident light 241 to fall on a wearer's eye 243 and is comprised of a light sensor 244 generating photocurrent 234; an integrating transimpedance amplifier 245 connected to light sensor 244 having sensitivity control 246 and an output photovoltage signal 235 proportional to photocurrent 234. Electronic circuit 240 further comprises a comparator 247 with voltage reference 253; a charging circuit 250 connected to capacitor 251 for charging a capacitor 251 having peak voltage reference 248, a voltage follower 254 connected to capacitor 251 and charging circuit 250; a pulse width modulator circuit 256 connected to the output of voltage follower 254 and driven by an oscillator 255, and a buffer amplifier 258 connected to PWM circuit 256 and to lens element 242 for driving lens element 242. PWM circuit 256 produces a PWM signal 259 of variable duty cycle and fixed period, the period being determined by oscillator 255.
Photovoltage signal 235 is connected to the input of comparator 247 which enables charging signal 237 a or discharging signal 237 b 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 237 a 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 237 b 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 237 a or 237 b 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%.
FIG. 8 is a block diagram of a third embodiment electronic circuit 260. Electronic circuit 260 provides electronic control of the transmissivity of lens element 282 allowing for a certain fraction of incident light 262 to fall on a wearer's eye 280 and is comprised of a DC/DC converter 265 connected to battery 266 and having output DC voltage Vcc 259 for powering the components of circuit 260; a light sensor 261 for sensing incident light 262; a crystal oscillator 267 oscillating at frequency f1; a square wave oscillator 283 oscillating at frequency f2 producing square wave signal 287 connected to a microprocessor 268 and an AND gate 284; microprocessor 268 having an A/D converter 264 connected to light sensor 261 and a timer 263 connected to crystal oscillator 267, microprocessor 268 further having memory 269 which contains program instructions 285 for operation and for generating a pulse width modulated signal; and a serial interface 271 for communications with microprocessor 268.
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 270 a and inverting buffer 270 b, a set of polarized capacitors 275 a and 275 b; a set of resistors 276 a and 276 b; and a set of diodes 277 a and 277 b. Both buffers having their inputs tied to PWM signal 273. Capacitor 275 a has its negative side connected to the non-inverting output 274 a of buffer 270 a and its positive side connected to the cathode of diode 277 a, to first end of resistor 276 a and to output line 278 a. The anode of diode 277 a and the second end of resistor 276 a are tied to ground. Capacitor 275 b has its positive side connected to the inverting output 274 b of buffer 270 b and its negative side connected to the anode of diode 277 b, to a first end of resistor 276 b and to output line 278 b. The cathode of diode 277 b and the second end of resistor 276 b are tied to ground. The voltage across output lines 278 a and 278 b 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 FIG. 10 below.
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.
FIG. 9 is a graph of a typical transmittance function 295 employed for direct view mode AVT eye glasses 10. The abscissa is the ambient luminance measured in cd/m²(L_in) and the ordinate is the transmissivity through lenses 12 and 14, the transmissivity being the fraction of light transmitted through the lens. The transmittance function 295 is typical of a fail dark mode of operation and is comprised of three regions, the controlled region 290, the fully powered transmittance region 291, and the powered off transmittance region 292. The fully powered transmittance region 291 transitions to the controlled region 290 at an ambient luminance of L1 corresponding to point 293 on the transmittance curve. The controlled region 290 transitions to the powered off transmittance region 292 at luminance L2 corresponding to point 294 on the transmittance curve.
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:
$T = {\begin{matrix} T_{\max} & L_{i} \leq L_{1} \\ a \log L_{i} + b & L & _{1} < L_{i} < L_{2} \\ T_{\min} & L_{i} \geq L_{2} \end{matrix}},$
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 the lenses 12 and 14, T_minis the minimum transmittance of the lenses 12 and 14, and the coefficients a and b are fit according to
$a = \frac{T_{\min} L_{2} - T_{\max} L_{1}}{\log L_{2} - \log L_{1}}, b = T_{\max} L_{1} - a \log L_{1} .$
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 of FIG. 10 shows two exemplary LCD response curves, a fail light mode response curve 500 and a fail dark mode response curve 501, both curves having duty cycle as the abscissa 503 and transmittance T as the ordinate 502. For a given lens assembly, the transmittance will take on a fixed maximum and a fixed minimum. In the fail light case according to curve 500, maximum transmittance point 504, occurs for small duty cycle and a minimum transmittance point 505, occurs near the point of maximum duty cycle, the maximum duty cycle being 50% in the exemplary embodiment. In the fail dark case according to curve 501, maximum transmittance point 508, occurs near the maximum duty cycle and minimum transmittance point 509, 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 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 FIG. 16. In practice, sensor response is approximately linear and the slope of sensor response curve 800 is typically stored in memory 269 as one of the set of parameters 286.
A useful feature of AVT eye glasses 10 is that the spectral response of the sensor approximate the response of the human eye. FIG. 17 shows graph 810 of a typical spectral response, the spectral response curve 820 being reasonably close to the response of the human eye 830. In the preferred embodiment using direct detection of ambient light, the light sensors 202, 244, and 261 are part APDS-9003 from Avago Technologies Corporation and the graphs of FIGS. 16 and 17 are taken from the corresponding data sheet.
Referring again to FIGS. 9 and 10 in operation, the desired transmittance T is computed from the overall transmittance response function 295 for a given ambient light level Li and then the duty cycle D for the desired transmittance T is derived from LCD response curve 500 to control the transmissivity of lenses 12 and 14. For ambient illumination less than L1 falling on the AVT eye glasses 10, lenses 12 and 14 are turned off transmitting light at a constant maximum lens transmittance, T_max. For ambient illumination greater than L2 falling on the AVT eye glasses 10, lens 12 and 14 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 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.
FIG. 11 is a pseudocode listing of a control program 300 executed by microprocessor 268 as program instructions 285 and controlling the various functions of AVT glasses. FIGS. 8, 9 and 10 are also useful to understanding the operation of control program 300. Control program 300 has a first hardware interrupt procedure 302, a second hardware interrupt procedure 315, a software interrupt procedure 306 executed at microprocessor boot up, a “Run” procedure 308 which executes the main loop of the program, and three subroutines 320, 325 and 327 which perform computational functions as explained below. A/D converter 264 is read to measure photodetector voltage referred to as photovoltage below. Timer1 is the internal timer 263 of microprocessor 268.
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 FIG. 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 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 FIG. 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 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 FIG. 10. T1 and T2 are the transmissivities at points 506 and 507 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 the linear function 510 or D_min; for T>T2, D is the minimum of the value given by the linear function 512 or D_max; otherwise D is the value given by the linear function 511.
Calibration of eyeglasses 10 is accomplished according to apparatus configurations shown in FIGS. 12A and 12B and according to the method shown in FIG. 13. The calibration method is suitable for eyeglasses using the digital electronic circuit 260 or similar. Similar calibration methods are conceived for the analog electronic circuits 200 and 240.
In FIG. 12A a first calibration configuration 650 for measuring light sensor response is shown. A computer 651 has an interface 654 to a calibrated light source 652, the interface 654 allowing for automatic programming of the luminant intensity of light source 652. Light source 652 is typically a diffuse source similar to Model RS-5 light source from Gamma Scientific corporation. Lenses 657 held within eyeglasses 658 are positioned to face the light source. A serial interface 653 is connected between computer 651 and eyeglasses 658 for reporting photovoltages measured by the light sensor of the eyeglasses. The light source may be moved laterally so that the field of view 655 of the light sensor on the eyeglasses may be determined.
FIG. 12B shows a second calibration configuration 660 suitable for calibrating the transmissivity of eyeglasses 658. Computer 651 has an interface 654 to calibrated light source 652, the interface 654 allowing for automatic programming of the luminant intensity of light source 652. The lenses 657 held within eyeglasses 658 are positioned to face the light source. A serial interface 653 is connected between computer 651 and the eyeglasses for programming the duty cycle of the PWM drive voltage for lenses 657 therein. A calibrated photodetector 665 is placed behind the eyeglass lens facing the calibrated light source 652 and made to detect light from the light source as transmitted through the lens, calibrated photodetector 665 connected to computer 651 by a computer interface 666. The computer has a program that can vary the duty cycle of lenses 657 and for each duty cycle, download the corresponding measured light intensity from calibrated photodetector 665. The values can be stored according to patient and product number for future reference.
FIG. 13 is a flowchart of a calibration method 600 used in conjunction with the first and second calibration configurations. The method begins in the step 601 wherein the PC calibration program is made to run on computer 651. The eyeglasses are also connected by interface 653 to computer 651 in step 602, the eyeglasses having the electronic circuit 260 therein. A calibration program is downloaded to the memory of the eyeglasses in step 604 using the interface 653. The calibration program contains program instructions to be executed by the microprocessor 268 to measure and communicate the photovoltage V from the eyeglasses light sensor. The calibration program also contains program instructions for accepting instructions via interface 653 to set the duty cycle of PWM signal that is driving lenses 657.
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 FIG. 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 for linear functions 510, 511 and 512. 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 the linear function 510, 511 and 512 are stored as LCD response coefficients 617. 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 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 FIG. 14, physicians program 700 is conceived for use alongside eyeglasses 10, 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 in step 702 which causes a Microsoft Windows program to operate in step 704. The Windows program checks that the eyeglasses are connected to the computer in step 708 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 in step 709. If the eyeglasses are connected to the computer and running a valid operational program, then a patient data screen is displayed in step 710. The physician then enters the patient data in step 714 and a desired lower light level L_min in units of cd/m2 in step 716. The physicians program 700 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 in step 719. If the light level is in range, then the patient data and the light level is downloaded to the eyeglasses in step 720 and a message to the effect that the eyeglasses have been successfully programmed is displayed in step 722. The physician's program ends at step 725 by exiting the program.
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.
FIG. 15 shows a typical physician's computer form display associated to the physician's program 700, the display fields being a patient name 750, patient street address 751, patient city address 752, patient state 753, patient zip code 754, date of service 755 and the minimum light level 760.
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.

Claims

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.