Ординатура / Офтальмология / Английские материалы / Step by Step Minimally Invasive Glaucoma Surgery_Garg, Melamed, Bovet, Pajic, Carassa, Dada_2006

362 Step by Step Minimally Invasive Glaucoma Surgery

sclera, 1–2 mm behind the limbus. Depending on the requirement, 28 spots are applied, also avoiding the 3 and 9 o’clock positions. Energy levels are titrated to avoid an audible “pop” which signifies an overtreatment and explosion of the ciliary body tissue.

The semiconductor diode laser (Iris Oculight SLx, Iris Medical Inc, Mountain View, CA, USA) emits at 810 nm wavelength and is better absorbed by melanin than the Nd:YAG. The spade shaped tip of the handpiece (known as the “G-Probe”) protrudes 0.7mm deeper than the contact surface. There is better absorption of this wavelength by the pigmented tissues of the ciliary body than the 1064 nm Nd:YAG laser. Also a lower incidenceof the complications seen with other cyclodestructive techniques namely, phthisis, hypotony, uveitis, pain, and loss of visual acuity are reported in the literature. The most widely adopted treatment strategy is the treatment protocol recommended by Spencer and Vernon. Here the laser energy was delivered through the 600 μm diameter quartz fiber oriented within the G-probe handpiece to center treatment 1.2 mm behind the limbus. Transillumination is recommended to identify the ciliary body position in eyes with congenitalglaucoma or where the limbal anatomy was distorted by previous surgery. The fibreoptic tip protrudes 0.7 mm from the G-probecontact surface in order to indent the conjunctiva and sclera thereby improving the laser transmission to the ciliary body. The posterior angulation of the fiber is ensured by simply placing the spade shaped tip flush with the limbus in the manner shown in the figure was correctly oriented to protect the lens of phakic eyes from laser damage. Their standard treatment protocol was used at each “session” to treat three quarters (270 degrees) of the circumference of the ciliary body. This usually resulted in 14. An energy of 2.0 W was used for 2.0 seconds,

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resulting in a power delivery of 4.0 J per application (56 J per session for 14 applications). This was not altered even if “pops” were heard during treatment. In the first treatment session the temporal 90 degrees was left untreated. A different 90 degrees was left untreated if further treatment sessions proved necessary. On subsequent treatments the 90 degrees untreated varied depending on the appearanceof the sclera and conjunctiva at the limbus—that is, if an area of scleromalacia from previous surgery was present this area could be avoided. In Spencer and Vernons (S&V) study, the mean IOP before treatment was 33.0 mm Hg (10.7) and by the last visit this had fallen to 16.7 mm Hg at 6 months. It is apparent that the cyclodiode gives a mean reduction of at least 33 percent in IOP. The visual acuity fell in half the patients by 1 line whenutilising the Iris diode laser with the G-probe. In their experience, when “pops” were heard continually with a consistent energy level they did not have any eyes with marked inflammation post-laser. They did not find a particular association between race and hearing “pops”.

Different protocols and treatment strategies are found in the literature.

Kosoko et al delivered between 17 and 19 applications to 270 degrees of the ciliary body for a 2.0 second period and commencing at 1.75W increasing to 2.0 W if no “pops” or “snaps” were heard. The theory behind reducing the energy so as not to hear “pops” at each application is that these are indicative of tissue disruption, thus leading to unwanted extra inflammation. No eyes in Kosoko and others’ multicenter study of 27 eyes had had a previous cyclodestructive procedure and only two eyes had repeat treatment (after 9 and 13 months).About 60 percent of eyes were controlled (IOP < 22 mm Hg) which is less than the figure of 81 percent from the S & V study.

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In a study carried out by Philip Bloom, they allowed more than one treatment session but 18 percent of their eyes had had cyclodestructive procedures before cyclodiode and the mean follow-up was only 10 months. In addition, the treatment protocol varied considerably between eyes, from 20 to 40 applications of 1.5 W and 1.5 seconds “titrated against risk of phthisis”.

Brancato et al 20 had a higher retreatment rate of 65 percent than Spencer and Vernons, 45 percent. This is probablydue to patient group differences as 10/48 patients in Brancato’s series had “pediatric glaucoma”.

Different types of glaucoma behaved differently. The rubeotic eyes, those with silicone oil glaucoma, those with glaucoma related to corneal disease (including postkeratoplasty glaucoma), and those with chronic posttraumatic glaucoma had the greatest percentage drop in IOP (56.7 to 65.6%) in the S & V study. These groups, however, had the highest pretreatment pressures and therefore would have required a larger dropto achieve the target pressure.

In our practice the following procedure is followed (Figs 22.5 to 22.11).

The eye to be operated, undergoes G-probe applications, over 360 degrees with the probe in the proper orientation, we use 2 watt power and 2 second exposure time. We aim for a “pop-less” endpoint. To simplify,I put 2 or 3 applications. If popping occurs, the energy is decreased in 0.5 watt increments till popping subsides,usually at 1.5 watts or sometimes even at 1 watt. Twenty-two applications are administered with care taken to avoid pigmented lesions on the conjunctiva, common pigmented Indian eyes. Also 3 and 9 o’clock meridians are best avoided to avoid pain, uveitis and ischemia which

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Fig. 22.11: Applying the G-probe laser energy

occurs with damage to the long ciliary nerves and vessels. The applications are put with firm indentation so as to maximize transmission of energy through the sclera and also as indentation leaves a mark which helps to position and space the next application. Once the applications are over, the eye is washed with betadine solution and cataract surgery is carried out ether with a standard 2.8 mm clear corneal phaco technique involving drect backcracking after tipping the nucleus up in hydrodissection in a procedure called lens salute phaco, or by employing a Microphaco technique and the same chopping maneuver with a Cyres Scythe chopping tip on the MST Duet inflow system.

In my (CM) experience, of combining phacoemulsification wth G-probe as a primary procedure for coexisting cataract and primary open angle glaucoma the dreaded complication, phthisis has never occurred, probably as

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these were “virgin” eyes and had not undergone any surgical intervention for glaucoma previously.

Phthisi bulbi in the literature review occurs in less than 1 percent of cases. Typically these patients have had 2 or three trabeculectomies and a healthy dose of cryotherapy as well. The G-probe application adds the final straw on the camels back so to speak!

Phthisis has never been reported in a case where no previous intervention (surgery or cryo) has been attempted in “virgin” eyes.

No patient had significant pain apart from a feeling of heaviness of the head.

Postoperatively the patient is typically on topical dexa or beta methasone eyedrops and Moxifloxacin eyedrops. Oral diclofenac sodium tablets 50 mg twice a day is all that is needed for any pain control for three to four days. Oral steroid is administered in a dosage of 16 mg triamcinolone tablets for 4 days.

There was no extra uveitis seen in these patients and no appreciable cells or flare, apart from that expected in a simple clear corneal phacoemulsification with a good quality viscoelastic.

This procedure in our hands has proved its safety and efficacy and deserves a try. When you consider, bleb failures, bleb leaks, bleb related endophthamlitis, overhanging blebs, bleb failure, persistent hypotony, maculopathy, etc. simply turning down the tap, may prove to be a more attractive alternative.

RESULTS

At the end of one day all patients had pressure less than 10 mm Hg. At week one, 3 patients had pressures greater than 21. At month 1 the number of patients (IOP > 21) had increased to 6.

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At month one these 6 underwent the same procedure again (G-probe). At month 6 all patients except one has pressures less than 21 mm Hg on no additional medication.

CONCLUSION

Combined G-Probe Phaco with IOL implantation has proved to be safe consistent and reproducibly easy to perform. It is a very effective way to control glaucoma without any incisional surgery!

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