reference is now made in detail to the exemplary embodiments of the invention , examples of which are illustrated in the accompanying drawings . wherever possible , the same reference numbers are used throughout the drawings to refer to the same or like parts . fig2 is a block diagram of an iop measuring system 200 according to the principles of the present invention . in fig2 , the iop measuring system includes power source 205 , iop sensor 210 , processor 215 , memory 220 , data transmission module 225 , and optional speaker 230 . power source 205 is typically a rechargeable battery , such as a lithium ion or lithium polymer battery , although other types of batteries may be employed . in addition , any other type of power cell is appropriate for power source 205 . power source 205 provides power to the system 200 , and more particularly to processor 215 . power source can be recharged via an rfid link or other type of magnetic coupling . processor 215 is typically an integrated circuit with power , input , and output pins capable of performing logic functions . in various embodiments , processor 215 is a targeted device controller . in such a case , processor 215 performs specific control functions targeted to a specific device or component , such as a data transmission module 225 , speaker 230 , power source 205 , or memory 220 . in other embodiments , processor 215 is a microprocessor . in such a case , processor 215 is programmable so that it can function to control more than one component of the device . in other cases , processor 215 is not a programmable microprocessor , but instead is a special purpose controller configured to control different components that perform different functions . memory 220 is typically a semiconductor memory such as nand flash memory . as the size of semiconductor memory is very small , and the memory needs of the system 200 are small , memory 220 occupies a very small footprint of system 200 . memory 220 interfaces with processor 215 . as such , processor 215 can write to and read from memory 220 . for example , processor 215 can be configured to read data from the iop sensor 210 and write that data to memory 220 . in this manner , a series of iop readings can be stored in memory 220 . processor 215 is also capable of performing other basic memory functions , such as erasing or overwriting memory 220 , detecting when memory 220 is full , and other common functions associated with managing semiconductor memory . data transmission module 225 may employ any of a number of different types of data transmission . for example , data transmission module 225 may be active device such as a radio . data transmission module 225 may also be a passive device such as the antenna on an rfid tag . in this case , an rfid tag includes memory 220 and data transmission module 225 in the form of an antenna . an rfid reader can then be placed near the system 200 to write data to or read data from memory 220 . since the amount of data typically stored in memory 220 is likely to be small ( consisting of iop readings over a period of time ), the speed with which data is transferred is not crucial . other types of data that can be stored in memory 220 and transmitted by data transmission module 225 include , but are not limited to , power source data ( e . g . low battery , battery defect ), speaker data ( warning tones , voices ), iop sensor data ( iop readings , problem conditions ), and the like . optional speaker 230 provides a warning tone or voice to the patient when a dangerous condition exists . for example , if iop is at a level that is likely to lead to damage or presents a risk to the patient , speaker 230 may sound a warning tone to alert the patient to seek medical attention or to administer eye drops . processor 215 reads iop measurements from iop sensor 210 . if processor 215 reads one or a series of iop measurements that are above a threshold , then processor 215 can operate speaker 230 to sound a warning . the threshold can be set and stored in memory 220 . in this manner , an iop threshold can be set by a doctor , and when exceeded , a warning can be sounded . alternatively , data transmission module may be activated to communicate an elevated iop condition to a secondary device such as a pda , cell phone , computer , wrist watch , custom device exclusively for this purpose , remote accessible data storage site ( e . g . an internet server , email server , text message server ), or other electronic device . in one embodiment , a personal electronic device uploads the data to the remote accessible data storage site ( e . g . an internet server , email server , text message server ). information may be uploaded to a remote accessible data storage site so that it can be viewed in real time , for example , by medical personnel . in this case , the secondary device may contain the speaker 230 . for example , in a hospital setting , after a patient has undergone glaucoma surgery and had system 200 implanted , a secondary device may be located next to the patient &# 39 ; s hospital bed . since iop fluctuations are common after glaucoma surgery ( both on the high side and on the low side which is also a dangerous condition ), processor 215 can read iop measurements made by an implanted iop sensor 210 . if processor 215 reads an unsafe iop condition , data transmission module 225 can alert the patient and medical staff via speaker 230 or by transmitting the unsafe readings to a secondary device . such a system is also suitable for use outside a hospital setting . for example , if an unsafe iop condition exists , processor 215 can operate speaker 230 to sound an audible warning . the patient is then alerted and can seek medical attention . the warning can be turned off by a medical professional in a number of ways . for example , when data transmission module 225 is an rfid tag , an rfid link can be established between an external device and system 200 . this external device can communicate with system 200 to turn off the speaker 230 . alternatively , an optical signal may be read by system 200 . in this case , data transmission module 225 has an optical receptor that can receive a series of light pulses that represent a command — such as a command to turn off speaker 230 . system 200 is preferably in a small , implantable , integrated package . as such , all of the components of system 200 can be built on a substrate , such as a semiconductor wafer , by any of a number of different processes . fig3 is a perspective view of an iop sensor according to the principles of the present invention . in fig3 , iop sensor 210 is a sealed cube with two photocells 325 & amp ; 330 , atop surface 310 , a side 315 , a light shield 320 and an optional light source 305 . top surface 310 of iop sensor allows light to enter the cube ( e . g ., it is transparent or translucent — a light permitting surface ). photocells 325 and 330 detect the amount of light entering the cube . light shield 320 at least partially blocks the light detected by photocell 330 . light shield 320 is fixed to side 315 . side 315 is flexible . therefore , as side 315 moves in response to a pressure change , the amount of light blocked by light shield 320 changes and the amount of light detected by photocell 330 also changes . side 315 may be thinner than the other sides , top 310 , and bottom of the cube so that side 315 is more flexible . the top 310 , bottom and other sides ( other than side 315 ) may be rigid or flexible . an optional light source 305 , as described below , is provided . alternatively , iop sensor may use ambient light entering the eye . while described as a cube , iop sensor 210 may be other geometric shapes that allow for deflection of side 315 and movement of attached shield 320 . the pressure inside the cube of iop sensor 210 is determined during the manufacturing process and can be about 0 kg / cm 2 , about 0 kpa , or about 0 psig . the cube of iop sensor 210 can be filled with any of a number of a variety of different gases , such as nitrogen , argon , sulfur hexafluoride , or the like . when the internal pressure is 0 kg / cm 2 , 0 kpa , or 0 psig ., side 315 will tend to deflect inward because the pressure inside the eye is higher than 0 kg / cm 2 , 0 kpa , or 0 psig . ( as shown in fig4 ). the configuration of photocells 325 & amp ; 330 shown in fig3 allows for a comparison between the light detected by photocell 325 and photocell 330 to be made . since photocell 325 is not shielded by light shield 320 , photocell 325 detects the “ full amount ” of light entering through top surface 310 . since photocell 330 is shielded by light shield 320 , photocell 330 detects less than the “ full amount ” of light entering through top surface 310 . a comparison between the amount of light measured by photocells 325 and 330 , therefore , can be used to determine the amount of deflection experienced by side 315 . the higher the external pressure , the greater the deflection of side 315 , and the less measured by photocell 330 . accordingly , the amount of light measured by photocell 330 indicates the amount of external pressure ( iop ). this use of two photocell ( 325 & amp ; 330 ) allows for the iop sensor 210 to work under different light conditions ( since ambient light conditions change ). for iop measurements , calibrating the iop sensor 210 is generally not critical . since a change in the amount of light detected by photocell 330 can be correlated with a magnitude of iop , a change in iop can be easily detected . generally , a series of light measurements taken over time corresponds to the relative magnitude of iop over time . more precise calibration of iop can be done in a doctor &# 39 ; s office , for example , by measuring iop in a traditional manner and correlating that measurement with a quantity of light measured by photocell 325 and 330 . optional light source 305 is typically an led . light source 305 may be mounted to or integrated with top surface 310 of iop sensor 210 . alternatively , iop sensor 210 may rely on ambient light ( and light source 305 is absent ). in another embodiment , a light source exterior to the eye can be used . for example , a light source may be attached to a hand held pressure reader and / or charger device that interfaces with iop sensor 210 . in this manner , an external light source ( which can be calibrated ) can be used to facilitate a pressure reading . iop sensor 210 can be manufactured via any of a number of different methods . for example , in a mems - based method , iop sensor 210 is built in layers . in this manner , layers of a biocompatible material are deposited to build iop sensor 210 . other vapor deposition methods , such as those used in the semiconductor industry , may also be employed . fig4 is a perspective view of an iop sensor according to the principles of the present invention . in fig4 , side 315 of iop sensor 210 is deflected inward . accordingly , light shield 320 is also deflected inward to partially obscure light reaching photocell 330 . in this manner , the internal pressure is less than the external pressure . the pressure difference determines how far light shield 320 moves and how much light photocell 330 detects . in other words , the distance that light shield 320 travels is dependent on the difference between the internal and external pressures . the distance that light shield 320 travels also determines the amount of light that is detected by photocell 330 . accordingly , the amount of light detected by photocell 330 ( as compared to the amount of light detected by photocell 325 ) indicates the difference between the internal and external pressures . such a light reading can be used to determine the change in iop . in another embodiment of the present invention , an array of iop sensors 210 ( shown in fig3 & amp ; 4 ) can be used together . in this configuration , more than one iop sensor 210 is attached to a substrate and then implanted in the eye . using more than one iop sensor 210 allows for redundancy and more accurate measurement of iop . as the number of iop sensors 210 in array increases , the statistical variance of the resulting iop measurement decreases ( and thus accuracy increases ). in another embodiment , multiple photodetector pairs can be used with a single light source to achieve redundancy . from the above , it may be appreciated that the present invention provides a system measuring iop . the present invention provides an iop sensor and associated peripherals . the present invention is illustrated herein by example , and various modifications may be made by a person of ordinary skill in the art . other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein . it is intended that the specification and examples be considered as exemplary only , with a true scope and spirit of the invention being indicated by the following claims .
an implantable intraocular pressure sensor system has a sealed geometric shape with an internal pressure at a first value . the sealed geometric shape has a first light permitting surface and a second flexible surface . a pair of photocells is located in the sealed geometric shape . a light shield is coupled to the second flexible surface . when the second flexible surface is deflected , a light measurement by the pair of photocells indicates an intraocular pressure condition .