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

32 Step by Step Minimally Invasive Glaucoma Surgery

the laser energy. Iris pigmentation of the lens is the only complication seen in 20 percent of the phakic patients treated.

Laser Sclerotomy in Pseudophakia and Aphakia

About 55 percent of the patients who underwent laser sclerotomy were already operated for cataract. Results varied according to the degree of pre-operative IOP and the type of glaucoma. A case of keratoplasty with pseudophakos was treated with this procedure. When impending ciliary staphyloma formation conventional trabeculectomy could not be performed. Also long-term use of anti-glaucoma medication has resulted in subconjunctival fibrosis. The laser sclerostomy in this case was useful.

34 Step by Step Minimally Invasive Glaucoma Surgery

INTRODUCTION

Zwing and Flocks in 1961 introduced for the first time the concept of using selectively Xenon Arc photocoagulation in the filtration angle of animals and reported lowering of intraocular pressure (IOP). Several workers tried this by different techniques of creating holes in trabecular meshwork (TM), but failed as the holes closed due to fibrous scarring. It goes to the credit of Wise and Witter in 1979, who described the successful protocol of laser trabeculoplasty.

ARGON LASER TRABECULOPLASTY

Indications

•Chronic open-angle glaucoma as initial treatment and as a supplement to maximum tolerable medical therapy

•Exfoliation syndrome

•Pigmentary glaucoma

•Open-angle glaucoma in aphakia and pseudophakia

•Previous history of single operation failed trabeculoplasty.

The best laser for trabeculoplasty is Green laser. A gonio

prism having antireflective coating on the front surface is best for visualizing the angle. Goldmann three mirror or single mirror lens can be used, but both of these require rotation of lens for viewing the 360° of angle. A Thorpe four-mirror gonioscopy lens can also be used. In this lens all the mirrors are inclined at 62°. The best lens, however is Ritch trabeculoplasty laser lens. It has two mirrors inclined at 59° for viewing the inferior quadrants and the other two at 64° for viewing the superior angle. It also has 17 D plano-convex button lens over the mirrors. This provides ×1.4 magnification and also reduces the 50 um

Laser Trabeculoplasty 35

spot to 35 um. Therefore we get a 35 um burn on the trabeculum. This produces a burn, which is slightly more than 35 um. Whereas, a 50 um spot produces a burn of 70 um or more, which causes more damage to TM and surrounding structures.

The Technique

Before beginning actual treatment with argon laser, the instrument should be made parfocal with the surgeon’s eyes. This can be accomplished by placing a paper as target at the same distance where patient’s eye is usually placed. The surgeon then focuses each eye separately on the paper. The aiming beam should make a round circle without any distortion. This makes the instrument parfocal with the surgeon’s eyes. The slit-lamp should be used with ×25 magnification. Too high a magnification can reduce the field whereas, too less magnification will provide with a reduced detail.

Preoperatively, Apraclonidine eye drops are instilled to reduce the chances of post-laser spike of IOP. Paracaine eye drops instilled immediately before the procedure is sufficient to give adequate anesthesia for placing Gonio lens in the eyes.

The laser settings are 50 um spot, 0.1 sec, energy of 400600 mw. In heavily pigmented trabeculum more energy may be required. The aim is to get a depigmentation spot or a gas bubble at the focussed site.

The laser beam is applied in between the pigmented and nonpigmented trabeculum. A posterior placement will burn iris and is likely to produce anterior synechia. Whereas, an anterior placement of the aiming beam can lead to corneal burn. We prefer to apply 50 laser shots on the inferior 180° and then watch the IOP for about three

Laser Trabeculoplasty 37

of macrophages, which phagocytose debris and thus clear the TM.

Complications

Transient Rise of IOP

This is the most commonly encountered complication after laser trabeculoplasty. In majority of the patients a mild rise of IOP occurs, which may remain high for a period for 24 hours only. The pressure starts rising with in 2 hours of trabeculoplasty. Therefore IOP should be rechecked within hours of the procedure. The next day usually the pressure comes down. Special care should be observed for those patients, who have advanced glaucoma. Apraclonidine 1 percent eye drops 1 hour prior and immediately after the procedure is instilled to prevent this complication.

Transient Mild Iritis

This is also a commonly seen complication in early postoperative period, especially in exfoliation syndrome and pigmentary glaucoma. Postoperatively, steroid eye drops prednisolone or fluoromethalone are given 6 hourly for at least 5-7 days.

Other Complications

•Corneal burn causing change in the size of corneal endothelial cells

•Formation of anterior synechia.

Results

The 5 years success rate with ALT is reported to be 50 percent, with a decrease of 6 to 10 percent per year. The

38 Step by Step Minimally Invasive Glaucoma Surgery

reduction in IOP is between 6 and 9 mmHg. The pressure reduction starts occurring after first day and continues for a period of one month. After this, usually the pressure reduction does not occur. The reduction caused by ALT may be sufficient for some eyes. But in others, it can only help in reducing the number eye drops that the patient is instilling in his eyes.

Factors Influencing the Response of ALT

1.Higher the pretreatment IOP more is the response. But if initial pressure has been more than 30 mmHg the response may not be very good.

2.Type of glaucoma.

Good Responders

•Chronic open-angle glaucoma

•Exfoliation syndrome

•Pigmentary glaucoma.

Fair Responders

•Open-angle glaucoma in aphakia and pseudophakia

•Previous history of single operation failed trabeculoplasty.

Poor Responders

•Previous history of multiple surgery

•Glaucoma associated with uveitis angle recession glaucoma

•Congenital or juvenile glaucoma

•Angle recession glaucoma.

Laser Trabeculoplasty 39

Repeat Trabeculoplasty

If 360° ALT has already been done and the desired reduction is not obtained a repeat trabeculoplasty may not be of any use. But if reduction has been achieved once, and the effect has reduced over a period of time, a repeat trabeculoplasty may be beneficial in some patients.

Comparison of Selective Laser Trabeculoplasty and ALT

Selective laser trabeculoplasty (SLT) is an alternative laser treatment introduced by Latina et al in 1995. SLT utilizes a Q switched, frequency doubled NdYAG laser ( = 532 nm) that selectively targets the pigmented TM cells without adversely affecting the TM in vitro, rendering the TM architecture more preserved. There have been a number of studies that compared the efficacyof ALT and SLT based on post-treatment IOP reduction, and all reported that SLT is as effective as ALT in terms of IOP lowering. In general, both modalities lower IOP an average of 5 mm of mercury 6 months post-treatment. Furthermore, compared to ALT, SLT did not cause ablation craters at the border of pigmented and non-pigmented cells in the TM, and the cellular changes induced by SLT did not extend beyond the Schlemm’s canal as it would after ALT. In addition, SLT appears not to cause the membrane formed by migrating endothelial cells in the necrotic TM seen after ALT treatment. SLT allows the use of 80 to 100 times lower levels of energy and less laser spots on the TM, causing less damage to the TM. Based on the above observations and results, SLT appears to be less destructive and may be more repeatable clinically than ALT.

40 Step by Step Minimally Invasive Glaucoma Surgery

BIBLIOGRAPHY

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