Cyclodestructive surgeries for glaucoma

Increased intraocular pressure is a major risk factor for glaucoma that ophthalmologists can control.

In order to effectively reduce intraocular pressure by reducing the production of fluid or increasing its outflow, medications (eye drops or tablets) are used. Most surgical and laser interventions, trabeculotomy, filtering operations, tubular shunts, goniotomy, iridectomy, laser trabeculoplasty and laser iridotomy reduce intraocular pressure by increasing the outflow. Cyclodestructive operations are aimed at destroying the ciliary body processes, reducing the production of intraocular fluid. Due to the unpredictability of these operations in terms of reducing intraocular pressure and the complications associated with their use, cyclodestructive operations are used last.

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Indications for cyclodestruction

Cyclodestruction of the ciliary body is usually reserved for patients who are refractory to medical or surgical treatment. Exceptions to this rule include patients who cannot undergo surgical treatment for medical reasons or in underdeveloped countries. In these countries, where medical treatment is expensive and rarely available, diode contact DPC, which is portable and relatively easy to perform, may in the future be the first-line treatment for glaucoma. Such procedures are useful in relieving the pain associated with glaucoma and the loss of vision, which may help the patient avoid enucleation until a malignancy is detected by ultrasound. These techniques have been used with varying degrees of success to treat end-stage open-angle glaucoma, neovascular glaucoma, blind painful eye, glaucoma after penetrating keratoplasty, progressive angle closure, both primary and secondary glaucoma, traumatic glaucoma, malignant glaucoma, silicone oil-induced glaucoma, congenital glaucoma, pseudophakic and aphakic open-angle glaucoma, and secondary open-angle glaucoma. Alternative treatments that may be used in these patient groups include fistulizing procedures using antimetabolites or tube shunts.

Contraindications to cyclodestruction

There are few contraindications to these operations. A direct contraindication is the presence of a crystalline lens and good vision. In these cases, alternative treatments should be used first. Severe uveitis is a relative contraindication, since severe inflammation occurs after the procedure: careful care is required before the procedure. However, uveitis glaucoma is one of the secondary glaucomas that is successfully treated with the described method. For all of the above methods, with the exception of endoscopic cyclophotocoagulation, the patient's cooperation is necessary, and its absence may be a contraindication.

Methods of cyclodestruction

Several methods are used for cyclodestruction: contactless transscleral cyclophotocoagulation (CPC), cyclocryotherapy, contact transscleral CPC, transpupillary CPC and endoscopic cyclophotocoagulation. If the desired pressure level has not been achieved, these interventions can be repeated as many times as necessary, usually at 1-month intervals.

Non-contact transscleral cyclophotocoagulation

A neodymium YAG laser is used to perform this operation. Previously, a semiconductor diode laser was used. A microlaser was also used. Retrobulbar anesthesia is administered. An eyelid speculum is inserted if a contact lens is not used. Sometimes a contact lens developed by Bruce Shields is used. The advantages of such a lens are: marks at 1 mm intervals for more accurate determination of the distance to the limbus, blocking part of the laser beams from entering the pupil, and anemization of the inflamed conjunctiva to reduce the superficial burn. At a distance of 1 to 3 mm from the limbus (optimally 1.5 mm), 8-10 burns are applied over 180-360°, avoiding the meridians at 3 and 9 o'clock, so as not to coagulate the long posterior ciliary arteries and thereby not cause necrosis of the anterior segments. They use energy of 4-8 J. The laser beam is focused on the conjunctiva, but the laser is dispersed in such a way that its effect falls exactly 3.6 mm below the surface of the conjunctiva, most of the energy is absorbed by the ciliary body. In general, the higher the levels of energy used, the greater the inflammation.

Contact transscleral cyclophotocoagulation

This technique is currently the most popular medium for cyclodestructive surgery. The procedure uses a relatively small contact laser semiconductor probe (G-probe; IRIS Medical Instruments, Inc., Mountain View, CA). Nd:YAG and krypton lasers are also used for contact transscleral CPC.

Method: Retrobulbar anesthesia is administered and a lid speculum is inserted. The patient is in a supine position. The anterior end of the probe is placed on the limbus.

Due to the design of the G-probe, the energy actually hits a point 1.2 mm from the limbus. Perform 30-40 applications of 1.5-2 W of energy for 1.5-2 sec at 360°, avoiding the 3 and 9 o'clock positions. If a popping sound is heard, reduce the energy by 0.25 V to prevent more severe inflammation and hyphema formation.

Cyclocryotherapy

In this technique, a 2.5 mm probe is cooled in liquid nitrogen to -80°C. It is then placed approximately 1 mm posterior to the limbus for 60 s. Treatment is performed in 2-3 quadrants, with four cryotherapy sessions per quadrant, excluding the 3 and 9 o'clock positions.

Transpupillary cyclophotocoagulation

A continuous wave of argon laser is directed using a biomicroscope. The method is based on the idea of direct action of laser energy on the ciliary processes instead of forced action through other structures such as the conjunctiva and sclera. To visualize the processes of the ciliary body, a Goldmann gonioprism, scleral depression and a large sectoral iridectomy are necessary. The laser action points are 50 to 100 μm in size with an energy of 700-1000 mW, the duration of each action is 0.1 s. The amount of energy used is selected so as to cause tissue blanching. Each visible process is treated in this way. The main disadvantage of this method is the difficulty of visualization.

Endoscopic cyclophotocoagulation

This technique is performed in the operating room under local retrobulbar anesthesia. There are two different approaches: limbal and through the pars plana. With the limbal approach, the pupil is maximally dilated, an approximately 2.5 mm incision is made with a keratome, and viscoelastic is inserted between the lens and the iris until the ciliary processes are reached. Through one incision, the processes can be treated at an arc of 180°. To treat the remaining 180°, a second incision must be made opposite the first. After the treatment of the processes is complete, the viscoelastic is washed out and the wound is sutured with 10-0 nylon. Cataract extraction can also be performed together with this procedure.

Endoscopic cyclophotocoagulation through the pars plana is performed only in aphakic or pseudophakic patients. A typical pars plana incision is made 3.5-4.0 mm from the limbus, an anterior vitrectomy is performed, and a laser endoscope is inserted. If more than 180 of the appendages need to be treated, two incisions are made. The scleral incisions are sutured with 7-0 vicryl. The laser endoscope contains a video conductor, a light guide, and a laser conductor in an 18- or 20-gauge endoprobe.

The 20-gauge probe has a field of view of 70 and a focal depth of 0.5 to 15 mm. The 18-gauge probe has a field of view of 110° and a focal depth of 1 to 30 mm. The probe is connected to a video camera, a light source, a video monitor, and a video recorder. A semiconductor diode laser with a wavelength of 810 nm is connected to the laser conductor. Laser exposures of 500-900 mW for 0.5 to 2 s are used to cause final whitening and wrinkling of each ciliary process. If a popping sound or the sound of bursting bubbles is heard, the duration and/or power of the exposure should be reduced. The surgeon performs the operation, observing his actions through a video monitor.

Post-operative care

All these treatments use glucocorticoids locally and under Tenon's capsule to relieve inflammation, which occurs in all patients. Sometimes atropine drops are prescribed. For pain, analgesics are used, ice is applied.

Complications of cyclodestruction

The most dangerous of these complications is chronic hypotension, leading to phthisis, which occurs in 8-10% of patients, and to sympathetic ophthalmia, which is observed less frequently. Severe pain occurs in approximately 50% of patients, it can last from several hours to several weeks, usually the pain subsides 2-3 days after the procedure. Pain is relieved by taking analgesics and applying ice.