Ординатура / Офтальмология / Английские материалы / Jaypee Gold Standard mini Atlas Series Lasik_Aragawal, Jacob_2009
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For all the above-mentioned reasons, we do not operate thyroid-affected patients, unless they suffer minor degrees of Graves’ disease without ophthalmopathy (Graves’ disease may present with or without ophthalmopathy) and are completely visually stable. We do never operate patients with Graves’ orbitopathy. The patient signs a special informed consent that informs of the increased risk of complications (e.g. dry eye, postsurgical diplopia).
In case of refractive surgery, in such patients, an adequate intensive corneal lubrication with preservativefree eye drops becomes essential.
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Figure 2.7A
Figure 2.7B
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Figure 2.7C
Figure 2.7D
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Figure 2.7E
Figures 2.7A to E: Femtosecond laser flap creation (Courtesy: Takeshi Ide and Terrence P O’Brien)
Although current automated mechanical microkeratomes have improved in design and safety to attain a high level of efficient clinical experience, outcome viability and patient anxiety remain concerns. In fact, flap creation with an automated mechanical microkeratome is responsible for considerable morbidity in LASIK, with intraoperative and postoperative complications occurring in a significant percents of cases.
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The complications most commonly involve mechanical abrasions of the epithelium, button-hole flap, incomplete flap, free cap, unintentional thin/thick flap, flap dislocation, diffuse lamellar keratitis (DLK), ectasia, macroand microstriae, and epithelial ingrowth. Even with normal function, the accuracy and precision of a mechanical microkeratome contrasts significantly with that of the submicron precision of the subsequent excimer laser ablation of the corneal stroma. Surgeon control of an automated microkeratome is limited, with little flexibility to accommodate individual surgical requirements imposed by corneal thickness, pupil location, or refractive state.
Development of a laser-based keratome was intended to address the shortcomings of traditional mechanical microkeratome technology, thereby improving the efficacy and safety of LASIK procedures. Femtosecond laser technology was chosen for this application because it has the capability to be delivered inside the corneal stroma with micron-level precision. Femtosecond solid-state lasers are gaining more popularity in many fields of medicine. With lamellar-based laser vision correction procedures, there is an evolving trend from automated mechanical to laser-assisted corneal flap creation (Figures 2.7A to E). Increasing familiarity with the concept of a “femtosecond
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laser” reinforces the notion that a femtosecond operates at very short time duration. Femtosecond lasers are mainly used for creation of the flap in LASIK surgery, even though there are numerous other evolving applications of the technology in ophthalmology.
Though difficult to comprehend as a basic level, the use of ultrashort pulses has a variety of potential advantages. In short, they include three principal advantages in time, space, and wavelength.
1.Time: Due to the ultrashort pulsation (pulse duration), it is possible to obtain a high-frequency pulse, high signal/noise (S/N) ratio, optical nonlinearity and high peak intensity. For example, this can be utilized in ultrahigh-speed optical transmission and signal processing.
2.Space: An ultrashort optical pulse occupies an extremely short distance in space and propagates at the velocity of light, and this means a possibility to precisely control the delay time in a small dimension and thus the overall optical device and circuit can be very compact.
3.Wavelength: Ultrashort pulse has a large spectral width due to the pulse shape-spectrum interdependence deduced directly from Fourier transform relationship, and this merits the use of various photonic functions in wavelength division, such as the extraction of multi-
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channel wavelengths from an ultrashort pulse, and also the wavelength conversion and pulse waveform shaping by applying this property. The extraction of 200 wavelength channels has been shown using a femtosecond pulse.
The first commercially available FDA-approved femtosecond laser applied in ophthalmology, the IntraLase(AMO, Santa Clara, CA,USA) has a considerable clinical experience with flap creation for LASIK.
Docking: A typical case begins with docking of the suction ring on the patient’s eye under the excimer laser microscope. Some doctors advocate marking the center of the pupil center with the surgical marking pen under the microscope as a centering guide. The suction ring and the cone on the laser port are applanated to give a fixed distance to facilitate application of the laser energy to a specific distance within the cornea.
Bed change: We then swing the patient’s bed from beneath the excimer laser to the IntraLase laser. (If swing bed is not available, patients move to IntraLase bed).
Adjustment: By squeezing the suction ring, we expand it a little bit to “grab” the docking cone and adjoin the laser to the cornea. When everything is aligned and the peripheral air meniscus part is gone after joystick steering, flap centration can be adjusted by the computer mouse
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to center the corneal cap on the pupil. Excessive mouse centration movement will reduce the corneal flap diameter. This is automatic reduction, though the caution appears on the screen. Therefore surgeons have to take care, especially when the treatment requires a large flap diameter (i.e. hyperopic treatment, high astigmatism treatment).
Laser: After achieving proper centration, the surgeon steps on the foot pedal to start the bed cut. The first pulses are delivered along the hinge. A pocket is first created for the gas generated during treatment to go into. Then, the raster pattern is used for bed making. This raster pattern was reported to be superior to spiral pattern with IntraLase. The laser puts down a layer of bubbles in a single predetermined plane at whatever flap depth has been set. The edge of the flap are prepared last with a variable angle chosen by the operator. Following IntraLase, the suction ring is released off (2nd Bed Change). We again swing the patient bed to the excimer laser.
(Lift the flap and Excimer Laser). The flap is lifted with a blunt spatula, starting next to the hinge and cutting bridging residual tissue. After lifting the flap, the excimer procedure is conducted.
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Figure 2.8A
Figure 2.8B
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Figure 2.8C
Figure 2.8D
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