Laser Treatments in the Chamber |
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Angle |
LASER is an acronym that stands for light amplification of stimulated emission of radiation. In simple terms it is parallel light of a certain wavelength. Laser light is used in different wavelengths to treat glaucoma. Tissues that can be treated are the iris, the trabecular meshwork to improve outflow facility and the ciliary body processes to reduce aqueous humor production.
9.1Thermal Lasers
9.1.1Laser Trabeculoplasty
In laser trabeculoplasty with thermal lasers, which include the argon laser in continuous wave mode (wavelength 488–514 nm; argon laser trabeculoplasty) and the diode laser (wavelength 810 nm; diode laser trabeculoplasty), heat from the laser beam induces burns, causing inflammation, which later forms scars. The trabecular tissue between two scarring spots is therefore open and outflow increases (mechanical theory).
The spots have a size of 50 mm. The duration of each pulse is 0.1 s. Spots (50–100, original count by Wise and Witter) are placed between the nonfunctional (anterior) and the functional (posterior) trabecular meshwork around 360°. The duration time depends on the amount of pigment and is between 400 and 1,200 mW. The laser spots should induce a grayish color in the trabecular meshwork, and tiny gas bubbles are possible. Application too close or at the ciliary band should be avoided. Peripheral anterior synechiae at a regular distance
are an unmistakable sign of an improperly applied argon laser trabeculoplasty. Use a contact lens which is designed for trabeculoplasty (Fig. 9.1).
9.1.2Argon Laser Suturolysis
If the (non-resorbable) sutures of the scleral flap in filtration surgery are too tight almost no filtering bleb will develop. Sometimes a gentle massage will help for a short time. It is advisable to perform a lysis of the black 10-0 nylon suture using a laser. Anesthetize the eye, and hold a Hoskins lens on the conjunctiva directly upon the suture to get a larger view. A diameter of 50 mm and a duration of 0.1–0.15 s are good settings. Never open more than one suture a day and check the outflow immediately. A filtering bleb should arise. At least one suture has to remain (Figs. 9.2 and 9.3).
9.1.3Argon Laser Peripheral Iridoplasty
Argon laser peripheral iridoplasty is a method to flatten the steep iris in plateau-iris configuration or plateau-iris syndrome. The heat of the laser burns the iris tissue which then shrinks, and this contraction opens the angle, thus avoiding iridotrabecular contact or formation of synechiae. The angle widens immediately. Due to the nerve supply to the iris this procedure might be painful, so inform the patient in advance. If necessary use a peribulbar block. The settings are: 0.5 ms, 500 mm diameter and about five
C. Faschinger, A. Hommer, Gonioscopy, |
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DOI 10.1007/978-3-642-28610-0_9, © Springer-Verlag Berlin Heidelberg 2012 |
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9 Laser Treatments in the Chamber Angle |
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Fig. 9.1 A contact lens designed for trabeculoplasty is placed on the cornea and the laser beam is exactly focused between the non-functional and the functional trabecular meshwork
Fig. 9.2 Hoskins lens for suturolysis. The suture is enlarged and can be clear visualized
Fig. 9.4 There are two patent Nd:YAG iridotomies (11 and 2 o’clock) and several scars in the periphery of the iris after argon laser peripheral iridoplasty in two rows. Before the iridoplasty the IOP increased despite patent iridotomies when the pupil was dilated
to seven spots per quadrant. Try to apply the spots as peripherally as possible. Sometimes you will need two lines to flatten the iris appropriately. Sometimes a wider pupil than before may result (Fig. 9.4).
9.1.4 Transscleral
Cyclophotocoagulation
Fig. 9.3 Argon laser suturolysis. Using the Hoskins lens one suture is easily opened and a filtering bleb should arise immediately
A diode laser (wavelength 810 nm) is applied transsclerally to destroy parts of the ciliary