Methods



DiathermyIn the natural sciences, the term diathermy [di?ah-ther″me] means "electrically induced heat" the use of high-frequency electromagnetic currents as a form of physical or occupational therapy and in surgical procedures. The term diathermy is derived from the Greek words dia and therma, and literally means “heating through.” It is commonly used for muscle relaxation. It is also a method of heating tissue electromagnetically or ultrasonically for therapeutic purposes in medicine. Diathermy is used in physical therapy and occupational therapy to deliver moderate heat directly to pathologic lesions in the deeper tissues of the body.Diathermy, whether achieved using short-wave radio frequency (range 1–100?MHz) or microwave energy (range 434–915?MHz), exerts physical effects and elicits a spectrum of physiological responses, the two methods differing mainly for their penetration capability.[1]Surgically, the extreme heat that can be produced by diathermy may be used to destroy neoplasms, warts, and infected tissues, and to cauterize blood vessels to prevent excessive bleeding. The technique is particularly valuable in neurosurgery and surgery of the eye.UsesPhysical therapyThe three forms of diathermy employed by physical and occupational therapists are ultrasound, short wave and microwave. The application of moderate heat by diathermy increases blood flow and speeds up metabolism and the rate of ion diffusion across cellular membranes. The fibrous tissues in tendons, joint capsules, and scars are more easily stretched when subjected to heat, thus facilitating the relief of stiffness of joints and promoting relaxation of the muscles and decrease of muscle spasms.UltrasoundUltrasound diathermy employs high-frequency acoustic vibrations which, when propelled through the tissues, are converted into heat. This type of diathermy is especially useful in the delivery of heat to selected musculatures and structures because there is a difference in the sensitivity of various fibers to the acoustic vibrations; some are more absorptive and some are more reflective. For example, in subcutaneous fat, relatively little energy is converted into heat, but in muscle tissues there is a much higher rate of conversion to heat.The therapeutic ultrasound apparatus generates a high-frequency alternating current, which is then converted into acoustic vibrations. The apparatus is moved slowly across the surface of the part being treated. Ultrasound is a very effective agent for the application of heat, but it should be used only by a therapist who is fully aware of its potential hazards and the contraindications for its use.Short waveShort wave diathermy machines utilize two condenser plates that are placed on either side of the body part to be treated. Another mode of application is by induction coils that are pliable and can be molded to fit the part of the body under treatment. As the high-frequency waves travel through the body tissues between the condensers or the coils, they are converted into heat. The degree of heat and depth of penetration depend in part on the absorptive and resistance properties of the tissues that the waves encounter.Short wave diathermy operations use the ISM band frequencies of 13.56, 27.12, and 40.68 megahertz. Most commercial machines operate at a frequency of 27.12?MHz, a wavelength of approximately 11 meters.Short wave diathermy usually is prescribed for treatment of deep muscles and joints that are covered with a heavy soft-tissue mass, for example, the hip. In some instances short wave diathermy may be applied to localize deep inflammatory processes, as in pelvic inflammatory disease.MicrowaveMicrowave diathermy uses radar waves, which are of higher frequency and shorter wavelength than radio waves. Most, if not all, of the therapeutic effects of microwave therapy are related to the conversion of energy into heat and its distribution throughout the body tissues. This mode of diathermy is considered to be the easiest to use, but the microwaves have a relatively poor depth of penetration.Microwaves cannot be used in high dosage on edematous tissue, over wet dressings, or near metallic implants in the body because of the danger of local burns. Microwaves and short waves cannot be used on or near persons with implanted electronic cardiac pacemakers.Hyperthermia induced by microwave diathermy raises the temperature of deep tissues from 41°C to 45°C using electromagnetic power. The biological mechanism that regulates the relationship between the thermal dose and the healing process of soft tissues with low or high water content or with low or high blood perfusion is still under study. Microwave diathermy treatment at 434 and 915?MHz can be effective in the short-term management of musculo-skeletal injuries.Hyperthermia is safe if the temperature is kept under 45°C or 113°F. The absolute temperature is, however, not sufficient to predict the damage that it may produce.Microwave diathermy-induced hyperthermia produced short-term pain relief in established supraspinatus tendinopathy.The physical characteristics of most of the devices used clinically to heat tissues have been proved to be inefficient to reach the necessary therapeutic heating patterns in the range of depth of the damage tissue. The preliminary studies performed with new microwave devices working at 434?MHz have demonstrated encouraging results. Nevertheless, adequately designed prospective-controlled clinical studies need to be completed to confirm the therapeutic effectiveness of hyperthermia with large number of patients, longer-term follow-up and mixed populations.[2]Microwave diathermy is used in the management of superficial tumours with conventional radiotherapy and chemotherapy. Hyperthermia has been used in oncology for more than 35 years, in addition to radiotherapy, in the management of different tumours. In 1994, hyperthermia has been introduced in several countries of the European Union as a modality for use in physical medicine and sports traumatology. Its use has been successfully extended to physical medicine and sports traumatology in Central and Southern Europe.SurgerySurgical diathermy is usually better known as " HYPERLINK "" \o "Electrosurgery" electrosurgery". (It is also referred to occasionally as " HYPERLINK "" \l "Electrocautery" \o "Cauterization" electrocautery", but see disambiguation below). Electrosurgery and surgical diathermy involve the use of high frequency A.C. electrical current in surgery as either a cutting modality, or else to cauterize small blood vessels to stop bleeding. This technique induces localized tissue burning and damage, the zone of which is controlled by the frequency and power of the device.Some sources[3] insist that electrosurgery be applied to surgery accomplished by high-frequency alternating current (AC) cutting, and that " HYPERLINK "" \l "Electrocautery" \o "Cauterization" electrocautery" be used only for the practice of cauterization with heated nichrome wires powered by direct current (DC), as in the handheld battery-operated portable cautery tools.TypesDiathermy used in surgery is of typically two types.Monopolar, where electrical current passes from one electrode near the tissue to be treated to other fixed electrode (indifferent electrode) elsewhere in the body. Usually this type of electrode is placed in contact with buttocks or around the leg.[5]Bipolar, where both electrodes are mounted on same pen-like device and electrical current passes only through the tissue being treated. Advantage of bipolar electrosurgery is that it prevents the flow of current through other tissues of the body and focuses only on the tissue in contact. This is useful in microsurgery and in patients with cardiac pacemaker.Diathermy risksAs with all forms of heat applications, care must be taken to avoid burns during diathermy treatments, especially to patients with decreased sensitivity to heat and cold. With electrocautery there have been reported cases of flash fires in the operating theatre related to heat generation meeting chemical flash points, especially in the presence of increased oxygen concentrations associated with anaesthetic.Concerns have also been raised regarding the toxicity of surgical smoke produced by electrocautery. This has been shown to contain chemicals which may cause harm by inhalation by the patients, surgeon or operating theatre staff.Laparoscopic Surgery in GynaecologyGenerally, there are two ways of performing gynaecological surgery: laparotomy and laparoscopy. Laparotomy is also the conventional open surgery, where an incision of several inches long is required. Two of the most common incisions for laparotomy in gynaecology are the lower midline incision, a vertical incision below the umbilicus, and the Pfannenstiel incision, a transverse incision just above the pubis. The laparoscopy, on the other hand, is performed through several small "keyhole" incisions in the abdomen, where instruments like a laparoscope (a thin telescope-like instrument), scissors and graspers are inserted. Figure 1: Four keyhole incisions in laparoscopy where trocars of diameter 10mm and 5mm are inserted. When is laparoscopy needed?Laparoscopy is performed either for diagnostic or operative purposes. Diagnostic laparoscopy is a procedure that allows the doctor to directly view the pelvic organs to investigate pelvic pain, infertility, suspected ectopic pregnancy, endometriosis, etc. Usually it is recommended when the cause or symptom of a disease cannot be confirmed via other diagnostic tests, such as ordinary questioning, physical examination, ultrasound and radiological (X-ray) examinations. Operative laparoscopy allows doctor to perform gynaecological surgeries at a minimally-invasive manner. Preparing for a Laparoscopy SurgeryPatient needs to be fasted for at least 6 hours before the surgery. In some surgeries, patient may be given medication to empty the bowel. How is Laparoscopic Surgery Performed?Laparoscopic surgery is performed under general anaesthesia. Prior to the laparoscopy, a Foley catheter may be inserted into the bladder to drain the urine during the surgery (see Figure 2). A 10 mm incision is made at the umbilicus and a Veress needle is inserted into the abdomen. The Veress Figure 2: A Foley catheter is inserted to empty the bladder prior to the surgery.needle is then connected to a CO2 insufflation tubing. Gas is passed into the abdominal cavity to distend the abdomen, so as to allow the doctor to see the pelvic organs and to perform the surgery more easily. A 10 mm trocar is placed at the umbilicus, followed by several 5 mm trocars, which are placed at the lower abdomen. A laparoscope attached to a video camera is passed through the 10 mm port. Video images captured by the video camera are displayed on a video monitor. A powerful light source is channelled into the abdominal cavity for illumination purpose. Instruments like laparoscopic scissors, graspers are also inserted through other 5mm ports to perform the surgery (see Figure 3). At the end of the surgery, all the instruments are removed and the CO2 gas is released. The incisions are either sutured or taped. In some patients, a drainage tube is left in the pelvis to drain out any fluid that may accumulate after the surgery. Figure 3: The laparoscopic surgery.Advantages of Laparoscopic SurgeryLess postoperative pain. In laparotomy, a large incision is usually made and the layers of the abdomen are separated in order to access the abdominal and pelvic organs. These layers are then sutured one by one on closure of the abdomen. On the contrary, only small punctures (keyholes) are made in laparoscopy. Thus, postoperative pain as a result of the wound healing is more severe in laparotomy than in laparoscopy. Quicker return of bowel function. Due to the fact that bowel is manipulated less in laparoscopy, the return of bowel function is faster in laparoscopy than in laparotomy. Quicker return to solid food.Quicker return to daily activities.Reduced chance of scar formation in the abdomen. In laparoscopy only fine instruments are used to perform the surgery whereas in laparotomy, the surgeon places his hands into the abdomen and pelvis to perform the surgery. Therefore, laparotomy has a higher likelihood of developing adhesions (scar tissue in the abdomen) than laparoscopy. This is especially important for patients who want to conceive because adhesions in the area of fallopian tubes and ovaries may lead to difficulty in conceiving. Reduced infection rate because of the small incisions and hence the internal organs are not exposed to the air in the operating room. Reduced bleeding during surgery. Shorter hospital stay.Smaller scars on the skin.Video magnification offers surgeon a better view of diseased organs and its surrounding vessels and nerves. Postoperative CarePatient is allowed to drink some clear fluids after surgery. Once she has passed flatus, she is allowed to consume other drinks and later solid food. The drainage tube in patient's bladder may be removed immediately after the surgery or several days later, depending on the type of surgery. For minor laparoscopic surgery, patient may resume normal activities and sexual intercourse within a few days. In major laparoscopic procedures, light physical activities can be performed in about one week. Sexual intercourse may only be possible after about six to eight weeks. Possible Postoperative Effects of Laparoscopic SurgeryAching of muscles.Discomfort and tiredness for up to five days.Increased urge to urinate because the CO2 insufflated during the surgery can apply pressure on the bladder. Nauseousness.Pain at the incision sites. Medication is usually prescribed to alleviate it. Period-like pain and a few days of vaginal bleeding or discharge. Shoulder pain for a few days because the CO2 insufflated can irritate the diaphragm, which shares the same nerves (predominantly the phrenic nerve) as the shoulder. Risks of Laparoscopic SurgeryAnaesthetic problems such as pneumonia.Bleeding caused by accidental injury to blood vessels or organs.Blood clot in the veins of the leg (deep vein thrombosis) or in the lung (pulmonary embolus). Incisional hernia.Infections of the incision sites or in the pelvis or abdomen.Leakage of body fluids due to accidental injury to bowel, bladder, ureter. If the injuries are detected during the surgery, emergency surgery is necessary to repair the damaged sites. This is usually done laparoscopically but sometimes a laparotomy may be needed. Otherwise, if the injuries are not detected immediately and are only discovered during the recovery period, a second surgery may be required. Certain patients may require blood transfusion during or after the surgery. Laparoscopic surgery, also called minimally invasive surgery (MIS), bandaid surgery, or keyhole surgery, is a modern surgical technique in which operations in the abdomen are performed through small incisions (usually 0.5–1.5?cm) as opposed to the larger incisions needed in laparotomy.Keyhole surgery makes use of images displayed on TV monitors to magnify the surgical elements.Laparoscopic surgery includes operations within the abdominal or pelvic cavities, whereas keyhole surgery performed on the thoracic or chest cavity is called thoracoscopic surgery. Laparoscopic and thoracoscopic surgery belong to the broader field of endoscopy.There are a number of advantages to the patient with laparoscopic surgery versus an open procedure. These include reduced pain due to smaller incisions and hemorrhaging, and shorter recovery time.The key element in laparoscopic surgery is the use of a laparoscope. There are two types: (1) a telescopic rod lens system, that is usually connected to a video camera (single chip or three chip), or (2) a digital laparoscope where the charge-coupled device is placed at the end of the laparoscope, eliminating the rod lens system.[1] Also attached is a fiber optic cable system connected to a 'cold' light source (halogen or xenon) to illuminate the operative field, inserted through a 5?mm or 10?mm cannula or trocar to view the operative field. The abdomen is usually insufflated, or essentially blown up like a balloon, with carbon dioxide gas. This elevates the abdominal wall above the internal organs like a dome to create a working and viewing space. CO2 is used because it is common to the human body and can be absorbed by tissue and removed by the respiratory system. It is also non-flammable, which is important because electrosurgical devices are commonly used in laparoscopic procedures.[2]Surgeons perform laparoscopic stomach surgery.Laparoscopic cholecystectomy is the most common laparoscopic procedure performed. In this procedure, 5–10?mm diameter instruments (graspers, scissors and clip applier) can be introduced by the surgeon into the abdomen through trocars (hollow tubes with a seal to keep the CO2 from leaking). Over one million cholecystectomies are performed in the U.S. annually, with over 96% of those being performed laparoscopically.There are two different formats for laparoscopic surgery. Multiple incisions are required for technology such as the da Vinci Surgical System, which uses a console located away from the patient, with the surgeon controlling a camera, vacuum pump, saline cleansing solution, cutting tools, etc. each located within its own incision site, but oriented toward the surgical objective. The surgeon's hands manipulate two haptic grippers which track hand movements and rotations while relaying haptic sensations back to the surgeon.Laparoscopic instruments.AdvantagesThere are a number of advantages to the patient with laparoscopic surgery versus an open procedure. These include:Reduced hemorrhaging, which reduces the chance of needing a blood transfusion.Smaller incision, which reduces pain and shortens recovery time, as well as resulting in less post-operative scarring.Less pain, leading to less pain medication needed.Although procedure times are usually slightly longer, hospital stay is less, and often with a same day discharge which leads to a faster return to everyday living.Reduced exposure of internal organs to possible external contaminants thereby reduced risk of acquiring infections.Although laparoscopy in adult age group is widely accepted, its advantages in pediatric age group is questioned. Benefits of laparoscopy appears to recede with younger age. Efficacy of laparoscopy is inferior to open surgery in certain conditions such as pyloromyotomy for Infantile hypertrophic pyloric stenosis. Although laparoscopic appendectomy has lesser wound problems than open surgery, the former is associated with more intra-abdominal abscesses.DisadvantagesWhile laparoscopic surgery is clearly advantageous in terms of patient outcomes, the procedure is more difficult from the surgeon's perspective when compared to traditional, open surgery:The surgeon has limited range of motion at the surgical site resulting in a loss of dexterityPoor depth perceptionSurgeons must use tools to interact with tissue rather than manipulate it directly with their hands. This results in an inability to accurately judge how much force is being applied to tissue as well as a risk of damaging tissue by applying more force than necessary. This limitation also reduces tactile sensation, making it more difficult for the surgeon to feel tissue (sometimes an important diagnostic tool, such as when palpating for tumors) and making delicate operations such as tying sutures more difficult.The tool endpoints move in the opposite direction to the surgeon's hands due to the pivot point, making laparoscopic surgery a non-intuitive motor skill that is difficult to learn.RisksSome of the risks are briefly described below:The most significant risks are from trocar injuries during insertion into the abdominal cavity, as the trocar is typically inserted blindly. Injuries include abdominal wall hematoma, umbilical hernias, umbilical wound infection, and penetration of blood vessels or small or large bowel.[8] The risk of such injuries is increased in patients who have a low body mass index[9] or have a history of prior abdominal surgery. While these injuries are rare, significant complications can occur, and they are primarily related to the umbilical insertion site. Vascular injuries can result in hemorrhage that may be life threatening. Injuries to the bowel can cause a delayed peritonitis. It is very important that these injuries be recognized as early as possible.[10]Some patients have sustained electrical burns unseen by surgeons who are working with electrodes that leak current into surrounding tissue. The resulting injuries can result in perforated organs and can also lead to peritonitis. This risk is eliminated by utilizing active electrode monitoring.There may be an increased risk of hypothermia and peritoneal trauma due to increased exposure to cold, dry gases during insufflation. The use of Surgical Humidification therapy, which is the use of heated and humidified CO2 for insufflation, has been shown to reduce this risk.[11]Many patients with existing pulmonary disorders may not tolerate pneumoperitoneum (gas in the abdominal cavity), resulting in a need for conversion to open surgery after the initial attempt at laparoscopic approach.Not all of the CO2 introduced into the abdominal cavity is removed through the incisions during surgery. Gas tends to rise, and when a pocket of CO2 rises in the abdomen, it pushes against the diaphragm (the muscle that separates the abdominal from the thoracic cavities and facilitates breathing), and can exert pressure on the phrenic nerve. This produces a sensation of pain that may extend to the patient's shoulders. For an appendectomy, the right shoulder can be particularly painful. In some cases this can also cause considerable pain when breathing. In all cases, however, the pain is transient, as the body tissues will absorb the CO2 and eliminate it through respiration.[12]Coagulation disorders and dense adhesions (scar tissue) from previous abdominal surgery may pose added risk for laparoscopic surgery and are considered relative contra-indications for this approach.Intra-abdominal adhesion formation is a risk associated with both laparoscopic and open surgery and remains a significant, unresolved problem.[13] Adhesions are fibrous deposits that connect tissue to organ post surgery. Generally, they occur in 50-100% of all abdominal surgeries [13]., with the risk of developing adhesions being the same for both procedures.[14][15] Complications of adhesions include chronic pelvic pain, bowel obstruction, and female infertility. In particular, small bowel obstruction poses the most significant problem.[14] The use of Surgical Humidification therapy during laparoscopic surgery may minimise the incidence of adhesion formation.[16] Other techniques to reduce adhesion formation include the use of physical barriers such as films or gels, or broad-coverage fluid agents to separate tissues during healing following surgery.[14]Robotic laparoscopic surgeryA laparoscopic robotic surgery machine.Non-robotic hand guided assistance systemsThere are also user-friendly non robotic assistance systems that are single hand guided devices with a high potential to save time and money. These assistance devices are not bound by the restrictions of common medical robotic systems. The systems enhance the manual possibilities of the surgeon and his/her team, regarding the need of replacing static holding force during the intervention.Some of the features are:The stabilisation of the camera picture because the whole static workload is conveyed by the assistance system.Some systems enable a fast repositioning and very short time for fixation of less than 0.02 seconds at the desired position. Some systems are lightweight constructions (18?kg) and can withstand a force of 20 N in any position and direction.The benefit – a physically relaxed intervention team can work concentrated on the main goals during the intervention.The potentials of these systems enhance the possibilities of the mobile medical care with those lightweight assistance systems. These assistance systems meet the demands of true solo surgery assistance systems and are robust, versatile, and easy to use.TonometryTonometry is a test to measure the pressure inside your eyes. The test is used to screen for glaucoma.How the Test is performed?There are several methods of testing for glaucoma.The most accurate method measures the force needed to flatten a certain area of the cornea.The surface of the eye is numbed with eye drops. A fine strip of paper stained with orange dye is touched to the side of the eye. The dye stains the front of the eye to help with the examination.The slit-lamp is placed in front of you, and you rest your chin and forehead on a support that keeps your head steady. The lamp is moved forward until the tip of the tonometer just touches the cornea. The health care provider looks through the eyepiece on the lamp and the machine gives a pressure reading. There is no discomfort with the test.A slightly different method uses a handheld device similar in shape to a pencil. Again, you are given numbing eye drops to prevent any discomfort. The device touches the outside of the eye and instantly records eye pressure.The last method is the noncontact method (air puff). In this method, your chin rests on a padded stand.You stare straight into the examining device. The eye doctor shines a light into your eye to properly line up the instrument, and then delivers a brief puff of air at your eye.The machine measures eye pressure by looking at how the light reflections change as the air hits the eye.How to Prepare for the Test?Remove contact lenses before the examination. The dye can permanently stain contact lenses.Tell your?health care provider if you have corneal ulcers and eye?infections?or?a history of glaucoma in your family. Always tell your doctor or nurse what medicines you are taking. How the Test Will Feel?If numbing eye drops were used, you should not have any pain. In the noncontact method, you may feel mild pressure on your eye.Why the Test is performed?Tonometry is a test to measure the pressure inside your eyes. The test is used to screen for glaucoma.People over age 40, especially African Americans, have the highest risk for developing glaucoma. Regular eye exams can help detect glaucoma early. If it is detected early, glaucoma can be treated before too much damage is done.The test may also be done before and after eye surgery.Normal ResultsA normal result means your eye pressure is within the normal range. The normal eye pressure range is 10 - 21 mmHg.How thick your cornea is can affect measurements. Normal eyes with thick corneas have higher readings and normal eyes with thin corneas have lower readings.?A thin cornea with a high reading may be very abnormal (the actual eye pressure will be higher than shown on the tonometer).Currently, a corneal thickness measurement (pachymetry) is needed to get a correct pressure measurement.Talk to your doctor about the meaning of your specific test results.What Abnormal Results Mean?Abnormal results may be due to:GlaucomaHyphemaInflammation in the eye Injury to the eye or headRisksIf the applanation method is used, there is a small chance the cornea may be scratched (corneal abrasion). This will normally heal itself within a few days.Alternative NamesIntraocular pressure (IOP) measurement; Glaucoma test; ApplanationEquipmentTonometer, either Goldmann (used on slit lamps) or Perkins (hand-held)Applanation prismLocal anaesthetic dropsFluorescein stripsClean cotton wool or gauze swabs.PreparationEnsure the prism has been disinfected with isopropyl alcohol 70% (methylated spirit) or sodium hypochlorite 1%. The prism must be rinsed in sterile water and wiped dry with a clean swab (residue of the disinfectant may cause a caustic burn on the cornea). Check that the graduation marked ‘0’ on the measuring prism is aligned with the white marker point on the tonometer headCheck the calibrated dial of the tonometer is set at 10 mmHgEnsure that the patient is sitting comfortably at the slit lamp: at the right height, with their chin on the rest and their forehead against the headband (or in a chair with their head supported, if using the Perkins tonometer)Set the magnification of the slit lamp at ×10.MethodInstil the local anaesthetic drops and then the fuorescein. Only a very small amount of fuorescein is neededFor measuring the IOP in the right eye, make sure the slit beam is shining onto the tonometer head from the patient's right side; for the left eye, the beam should come from the patient's left sideMove the filters so that the blue filter is used to produce a blue beamMake sure the beam of light is as wide as possible, and that the light is as bright as possible. This makes visualising the fluorescein rings easier (with the slit diaphragm fully open)Ask the patient to look straight ahead, open both eyes wide, fix his or her gaze and keep perfectly stillWith the thumb, gently hold up the patient's top eyelid, taking care not to put any pressure on the eyeDirect the blue light from the slit lamp or the Perkins tonometer onto the prism headMake sure that the tonometer head is perpendicular to the eyeMove the tonometer forward slowly until the prism rests gently on the centre of the patient's corneaWith the other hand, turn the calibrated dial on the tonometer clockwise until the two fluorescein semi-circles in the prism head are seen to meet and form a horizontal ‘S’ shape. (Note: the correct end point is when the inner edges of the two fluorescein semi-circle images just touch)Note the reading on the dial and record it in the notesWithdraw the prism from the corneal surface and wipe its tipRepeat the procedure for the other eyeWipe the prism with a clean, dry swab and replace it in the receptacle containing the disinfectant. HYPERLINK "" \t "tileshopwindow" Applanation tonometry. UKApplanation tonometry rings viewed through the Goldmann prismHigh intraocular pressure before the end point is reached will result in this image. Continue to turn the calibrated dial on the tonometer clockwise to reach the correct end point.Low intraocular pressure will result in this image. Turn the calibrated dial on the tonometer anticlockwise to reach the correct end point.This is the correct end point - the inner edges of the rings are just touching. This will give a correct reading of intraocular pressure.Calibration of the Goldmann tonometerIt is possible to check the calibration of the tonometer; this should be done every six months. Calibration is done at dial positions 0, 2, and 6 (equivalent to 0, 20, and 60 mmHg)Insert the prism in the holder and place the tonometer on the slit lampAt dial position 0, the feeler arm should be in free movement. If the dial is turned backwards a small way (to the equivalent of position -0.05), the arm should fall towards the examiner. If the dial is turned forwards a small way (to the equivalent of position +0.05) the arm should fall towards the patientIf the arm doesn't respond in the above way, the tonometer is inaccurate at dial position 1To check dial positions 2 and 6, the check weight is used (this is normally found in the case with the tonometer prisms or in the drawer of the slit lamp). There are five markings engraved on the bar. These represent 0 centrally, then 2 on either side, and 6 towards the edgesLine up the adjustable holder with index mark 2 on the weight. With the longer end of the bar facing you, put it into the slot on the side of the tonometer and push it all the way inRepeat the above steps (for dial position 0), with the dial now at position 2. This time, turn the dial backwards to the equivalent of 1.95 and forwards to the equivalent of 2.05To check dial position 6, move the weight bar to the end position. Repeat the steps at dial position 6, turning the dial backwards to the equivalent of 5.9 and forwards to the equivalent of 6.1If the tonometer is inaccurate at any of these dial positions, it should be returned to the manufacturer for recalibration.A Goldmann tonometerMethodsSemicircles seen during Goldmann tonometry through slit lampThe PASCAL dynamic contour tonometerDiaton transpalpebral tonometerApplanation tonometryIn applanation tonometry the intraocular pressure is inferred from the force required to flatten (applanate) a constant area of the cornea, for the Imbert-Fick law.[1] The Maklakoff tonometer was an early example of this method, while the Goldmann tonometer is the most widely used version in current practice.[citation needed] Because the probe makes contact with the cornea, a topical anesthetic, such as proxymetacaine, is introduced on to the surface of the eye in the form of an eye drop.Goldmann tonometryGoldmann tonometry is considered to be the gold standard test and is the most widely accepted method.[2][3] A special disinfected prism is mounted on the tonometer head and then placed against the cornea. The examiner then uses a cobalt blue filter to view two green semi circles. The force applied to the tonometer head is then adjusted using a dial connected to a variable tension spring until the inner edges of the green semicircles in the viewfinder meet. When an area of 3.06mm has been flattened, the opposing forces of corneal rigidity and the tear film are roughly approximate and cancel each other out allowing the pressure in the eye to be determined from the force applied. Like all non-invasive methods, it is inherently imprecise.[4]Perkins tonometerThe Perkins is a type of portable applanation tonometer, useful in children, patients unable to co-operate with a sitting slit lamp examination or in anesthetised patients who need to lie flat.[citation needed]Dynamic contour tonometryDynamic contour tonometry (DCT) uses the principle of contour matching instead of applanation. The tip contains a hollow the same shape as the cornea with a miniature pressure sensor in its centre. In contrast to applanation tonometry it is designed to avoid deforming the cornea during measurement and is therefore thought to be less influenced by corneal thickness and other biomechanical properties of the cornea than other methods but because the tip shape is designed for the shape of a normal cornea, it is more influenced by corneal curvature.[5]The probe is placed on the pre-corneal tear film on the central cornea and the integrated piezo-resistive pressure sensor automatically begins to acquire data, measuring IOP 100 times per second. The tonometer tip rests on the cornea with a constant appositional force of one gram. When the sensor is subjected to a change in pressure, the electrical resistance is altered and the tonometer's computer calculates a change in pressure according to the change in resistance. A complete measurement cycle requires about 8 seconds of contact time. The device also measures the variation in pressure that occurs with the cardiac cycle. Non-contact tonometryNon-contact tonometry (or air-puff tonometry) is different from pneumatonometry and was invented by Bernard Grolman of Reichert, Inc (formerly American Optical). It uses a rapid air pulse to applanate (flatten) the cornea. Corneal applanation is detected via an electro-optical system. Intraocular pressure is estimated by detecting the force of the air jet at the instance of applanation.[9] Historically, non-contact tonometers were not considered to be an accurate way to measure IOP but instead a fast and simple way to screen for high IOP. However, modern non-contact tonometers have been shown to correlate well with Goldmann tonometry measurements and are particularly useful for measuring IOP in children and other non-compliant patient groups. ................
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