9.2 Non-thermal Lasers

processes to decrease the production of aqueous humor. The probe automatically gives you the appropriate distance to the limbus. The treatment involves the application of 20–25 spots with 2,000 mW power and 2,000 ms exposure time over three-quarters of the circumference. Spare the 3 and 9 o’clock positions because of the long anterior ciliary vessels (Fig. 9.5). If you hear a “pop” (a sign of microexplosion of tissue) the energy level is too high. Better efficacy and safety may be reached with a controlled application of the laser spots (con- trolled coagulation, COCO; power 5,000 mW, exposure time 500 ms).

9.1.5Endoscopic Cyclophotocoagulation, Endocycloplasty

A 20-gauge curved laser probe (diode, 810 nm, with a fiber optic camera) is inserted into the eye posterior to the iris to treat the ciliary processes. It is primarily used in combination with phacoemulsification. The ciliary processes are partially destroyed by the heat and will produce less aqueous humor. Each ciliary processus is treated over at least 270°.

Endocycloplasty is the same procedure, but with less power (250–350 mW), so no destruction but only shrinkage of the ciliary processes will occur. Indications are eyes with cataract and plateau-iris syndrome.

9.2Non-thermal Lasers

9.2.1Selective Laser Trabeculoplasty

In selective laser trabeculoplasty a frequencydoubled Nd:YAG laser (wavelength 532 nm) in pulsed mode is used and the target of treatment are the melanocytes of the trabecular meshwork. The treatment leads to the release of cytokines, activation of macrophages and disassembly of the intercellular junctions. The destructive elements are much less than in argon laser trabeculoplasty. Different settings for the laser beam parameters are used. Because of the larger diameter, exact focusing is not as important as in argon laser trabeculoplasty. The center of the large beam should be aimed at the trabecular meshwork (Fig. 9.6). Do not cover the iris. The delivered energy is 100-fold less than in argon laser trabeculoplasty. The exposure time is preset and is 3 ns. In a heavily pigmented trabeculum you will need less energy, and a treatment over 90° might be sufficient. The therapy end-points are

Fig. 9.5 The probe of the diode laser is set perpendicular on the limbal region. The laser acts 1.5 mm behind. The red light is from the aiming beam

Fig. 9.6 The argon laser spots in argon laser trabeculoplasty are located between the functional and non-functional trabecular meshwork (red dots) and the Nd:YAG laser spots in selective laser trabeculoplasty are located on the functional and non-functional trabecular meshwork (yellow dots)