Please use this identifier to cite or link to this item: http://hdl.handle.net/11527/16197
Title: Yeni Bir Fakoemülsifikasyon Cihazı Tasarımı Ve Uygulaması
Other Titles: Design And Application Of A New Phacoemulsification Device
Authors: Elçioğlu , Mustafa
Halıcı, Hüseyin
152270
Elektronik Mühendisliği
Electronics Engineering
Keywords: Elektrik ve Elektronik Mühendisliği
Electrical and Electronics Engineering
Issue Date: 2004
Publisher: Fen Bilimleri Enstitüsü
Institute of Science and Technology
Abstract: This doctoral thesis covers design, realization and clinical application of a new phacoemulsification apparatus for cataract surgery. The eyes, the most important organs of humans, provide 80% of human perception. The eye is a sphere with a diameter of 23 mm. It has three layers, hard layer (sclera), vein layer, (uvea) and nerve layer (retina), from outside to inside respectively (Figure 1). Some other important structures in the human eye are cornea, iris, pupil, front chamber and lens. Vitreus is a jel-like tissue that fills the inner back part of the eye. SCLERA UVEA LENS RETINA ~__^_- ">a- -^ VITREUS Figure 1 Detailed appearance of three layers of eye and cornea, anterior chamber and lens. The 'CORNEA', the transparent layer of eye in the front, and the 'LENS' are the optical systems of the eye. The 'FRONT CHAMBER' is the space between the cornea and the iris. It is filled with a transparent liquid like water. Cornea principally consists of three layers, epithelium, stroma and endothelium, from outside to inside, respectively. Epithelium has the ability to renew itself. Stroma is the layer that provides the strength of the cornea. Endothelium is the innermost layer and it consists of a single layer of cells that cannot renew themselves. Its main function is to pump out excess liquid out of the stroma and enable the cornea to stay transparent. Lens is a biconvex, veinless, colorless, transparent, 4-5 mm thick structure of 9 mm diameter behind the pupil. Its basic function is to provide precise adjustment for focusing, just like the lens of a camera. XXIV The rays reflected off the things we look at, are at first refracted by the transparent layer (cornea), then the lens, and finally focused on the 'retina' at the back of the eye. The retina contains nerve fibers that transmit the "picture" to the visual center in the brain where vision is accomplished. The human lens gradually loses its transparency after the 60's; in other words it becomes opaque. This condition is called 'cataracts'. The lens is located behind the iris and it focuses incoming light onto the "receiver cells'' on the nerve layer in the retina. As a result of the lens becoming more opaque, that is, the development of cataracts, the amount of light reaching the retina decreases, and thus, vision is affected. A treatment to reverse or prevent cataract development is still to be found. Therefore, the only treatment of cataracts is a removal operation. Nowadays, treatment of cataracts is based on the surgical extraction of the opaque lens and insertion of an acrylic man-made lens in its place. Depending on the surgical technique, the length of the cut on the eye surface varies. Currently, the main aim is to enter the eye through a cut as short as possible. The shorter the surgical cut, the shorter the recovery period. The cut length decreased from 14 mm of 15 years ago to 2.8 mm with the development of phacoemulsification technique. Phacoemulsification involves (i) tearing apart of the lens in the natural liquid environment of the eye with ultrasonic energy, and (ii) aspiration of the remnants by vacuum through the small surgical cut made to enter the front chamber. Phacoemulsification was made up of two words: (1) phacos' meaning lens in Greek language, and (2) 'emulsification' meaning liquid with hard particles in it. Superiority of phacoemulsification operations over classical cataract operation (EKKE) can be summarized as follows. (1) duration of the operation is decreased; (2) as a result of entering the eye from a small cut, there is usually no need for stitches; (3) as the operational cut becomes smaller, the recovery is quicker; (4) astigmatism (optical distortion) decreases or even vanishes due to small cut; (5) the patient returns to work and use his/her operated eye sooner; and (6) frequency and number of controls after the operation decreases. THE PHACOEMULSIFICATION SYSTEM DEVELOPED The general structure of the phacoemulsification system developed is given in Figure 2. The phacoemulsification system consists of a main unit controlling the whole system and providing communication via a 7,7" colored screen tactilematic operator panel, a phaco unit, irrigation and aspiration (l/A) units, vitrectomy and diathermy units, custom designed footswitch pedal, vacuum sensor, irrigation pinch valve, phaco with step motor, vitrectomy and diathermy probes. 5 microcontrollers (Microchip, PIC18F452, 8 bits, 64 Kbyte program memory) were used to control the above-mentioned units, to process incoming signals from outside, and to provide communication of units with one another. XXV OIIKAİOH PANII L. MASTFR UNIT l-IIAtti [Ml II Mlh A I U Hi UN II PHACO SIGNAL IRRIGATION PINCH VALF [RIGATION ILigUID FLOIHr> ll'KHif.lliVI =H AM II 'A Ih IN I INI I (STEP MOTOR PERISTALTIC PUMP (U' ASPIRATION QUID ABSORB.) m PHACO PROBE I VACUUM 1 SENSOR uiimi > iur.iv unu PNEUMATIC PULS VITRECTOMY PROBE MEMORY DIAIIKMV UNIT DIATERMY SIGNAL D1ATERMY PROBE PEDAL footswitch Figure 2. The structure of the developed phacoemulsification system. The tactilematic operator panel is used for recording preset values, visualization of the current settings on the screen and other visual effects. Memory unit contains user information about phaco, l/A, vitrectomy and diathermy settings. Phacoemulsification unit drives the phaco probe, ultrasonic energy is produced and controlled. I/A unit controls the step motor and irrigation pinch valve using the signals coming from the vacuum sensor and foot pedal. Vitrectomy unit drives the pneumatic probe by a rapid valve. Diathermy unit provides a high frequency signal to the diathermy probe for cauterization purposes. All controls are accomplished using a footswitch pedal. The pedal is connected directly to the main unit. Analog signals from the pedal potentiometer as well as digital signals from the 4 side switches of the pedal are sensed by the main unit. All the signals are sent to each and every unit by serial communication. Moreover, by means of 3 serial EEPROMs, all system parameters, such as, operation and user settings are saved. The phaco apparatus is controlled with a footswitch pedal by the surgeon/operator whose hands are presumed engaged. The pedal designed for the system has 4 vertical linear displacement levels, '0', T, '2', '3', and 4 side switches, upper switch, left side switch, right side switch and back switch. In position '1', irrigation liquid flows, that is, irrigation pinch valve opens and liquid flows from the sterile irrigation bottle to the eye. In position '2', the head of the pump starts to turn at a previously set speed, and an aspiration current is established in addition to the above described functions of position '1. XXVI In position '3', ultrasonic energy is delivered in addition to the functions of level T and '2'. In this level, the ultrasonic power increases linearly with the displacement of the foot pedal. LEFT SIDE SWITCH ÎFflKOtel'.-"'''».' CLO5E0 1. POSITION 2.P05ITION 3.POSITION BACK SWITCH (comnne irwsaswi) TOP SWITCH (REFLUX) RIGHT SIDE SWITCH (PROGIWMIssllwII» Figure 3. The unique foot pedal used in our system '0' position is the highest point and there is no current in this level (standby mode). Upper switch: Normally, reflux operation is controlled with the pedal upper switch. When you press this switch, reflux function is activated for 200 ms. This function is provided by the irrigation flow to the aspiration tube by means of the pinch valve. If the apparatus is in the test phase, by pressing this switch you return to the previous step. Left side switch: This switch is located in the left inner side of the pedal. It makes possible transitions between phaco, l/A, diathermy, again phaco units (in this order) by each press. Right side switch: This switch is located in the right side of the pedal. It is for changing the active operation value in phaco, l/A, diathermy and vitrectomy units. Back switch: This switch is located on the exterior upper part of the pedal. With one press irrigation pinch valve becomes active and with a second it becomes passive (in other words toggle). It controls irrigation mode between continuous flow or flow depending on the pedal displacement (Level 1). Various modes were developed for (1) decreasing both the total phaco energy applied to the eye, (2) decreasing the effect of heat, and (3) sensitive control. These are gathered under three main groups as standard (continuous), interrupted, vacuum (occlusion threshold) modes. Standard continuous modes: In these modes, phaco power is applied without interruption. These are of two types, one is constant, the other is proportionally increasing power. Interrupted modes: These modes are for interrupted application of phaco power. These are divided into 3 groups as pulse modes, burst modes and mini-burst modes. In our apparatus, 120 ms periods are used for pulse modes. Pulses are 40 ms, 60 ms, 80 ms long or applied PWR. The third displacement level of the pedal in PWR mode is divided into sublevels between 0% and 100%. 40 ms, 60 ms, 80 ms or continuous phaco power are applied depending on the sublevel. There are 3 burst modes as continuous burst, multi burst and single burst. In continuous burst mode, constant phaco power is applied during the predetermined 120 ms on time. However, the total period (on time plus off time) shortens linearly with displacement of the foot pedal from 2000 ms to 200 ms. Beyond 90% XXVII OIIKAİOH PANII L. MASTFR UNIT l-IIAtti [Ml II Mlh A I U Hi UN II PHACO SIGNAL IRRIGATION PINCH VALF [RIGATION ILigUID FLOIHr> ll'KHif.lliVI =H AM II 'A Ih IN I INI I (STEP MOTOR PERISTALTIC PUMP (U' ASPIRATION QUID ABSORB.) m PHACO PROBE I VACUUM 1 SENSOR uiimi > iur.iv unu PNEUMATIC PULS VITRECTOMY PROBE MEMORY DIAIIKMV UNIT DIATERMY SIGNAL D1ATERMY PROBE PEDAL footswitch Figure 2. The structure of the developed phacoemulsification system. The tactilematic operator panel is used for recording preset values, visualization of the current settings on the screen and other visual effects. Memory unit contains user information about phaco, l/A, vitrectomy and diathermy settings. Phacoemulsification unit drives the phaco probe, ultrasonic energy is produced and controlled. I/A unit controls the step motor and irrigation pinch valve using the signals coming from the vacuum sensor and foot pedal. Vitrectomy unit drives the pneumatic probe by a rapid valve. Diathermy unit provides a high frequency signal to the diathermy probe for cauterization purposes. All controls are accomplished using a footswitch pedal. The pedal is connected directly to the main unit. Analog signals from the pedal potentiometer as well as digital signals from the 4 side switches of the pedal are sensed by the main unit. All the signals are sent to each and every unit by serial communication. Moreover, by means of 3 serial EEPROMs, all system parameters, such as, operation and user settings are saved. The phaco apparatus is controlled with a footswitch pedal by the surgeon/operator whose hands are presumed engaged. The pedal designed for the system has 4 vertical linear displacement levels, '0', T, '2', '3', and 4 side switches, upper switch, left side switch, right side switch and back switch. In position '1', irrigation liquid flows, that is, irrigation pinch valve opens and liquid flows from the sterile irrigation bottle to the eye. In position '2', the head of the pump starts to turn at a previously set speed, and an aspiration current is established in addition to the above described functions of position '1.
Description: Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2004
Thesis (Ph.D.) -- İstanbul Technical University, Institute of Science and Technology, 2004
URI: http://hdl.handle.net/11527/16197
Appears in Collections:Elektronik Mühendisliği Lisansüstü Programı - Doktora

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