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

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Pre-laser Workup

All patients are initially given a trial of pupillary dilatation by 2 percent homatropine and 10 percent phenylephrine eye drops (rule out hypertension) after which additional dilatation is tried by tropicamide 1 percent eye drops. One percent Atropine eye ointment is used in twice daily dosage on a long-term basis in these patients. Informed consent must be obtained.

Technique of Laser Therapy

They are seated on a Q-switched Nd:YAG laser machine and an Abraham type of iridotomy lens is used. The synechiae are cut by 1mJ of power by focusing the laser towards the iris rather than the lens surface starting in the inferior quadrant so that the debris and hemorrhage are not dispersed in the anterior chamber, impeding further laser. If excess debris and hemorrhage are dispersed in the anterior chamber then the next sitting is tried after 30 minutes and if again visualization is inadequate then the procedure is carried out after 48 hours.

Postoperatively IOP is recorded hourly for 4 hours, then at 12 hours and thereafter daily till 7 days. It is also recorded subsequently whenever patient visits the outpatient department. Dilatation is tried by putting 2 percent homatropine and 10 percent phenylephrine drops starting immediately after laser at every 5 minutes for 30 minutes (Fig. 6.2). Patients are continued on antiglaucoma medications of 0.25 percent timolol maleate BD along with 1 percent tropicamide eye drops four times daily for 2 weeks. Postoperatively pupillary diameter, change in visual acuity along with any lenticular damage is recorded.

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Fig. 6.2: Dilatation of pupil after YAG laser synechiolysis

Clinical Results

A study was conducted at Dr RP Centre for Ophthalmic Sciences, New Delhi (unpublished data) to evaluate the above technique. Fifteen patients of chronic granulomatous uveitis with bound down pupil or presence of ring synechiae where dilatation was not possible by pharmacological means were chosen for the study. Shallow anterior chamber, hazy cornea, active anterior uveitis and secondary glaucoma formed the contraindications to such a laser therapy. Each patient also has an associated complicated cataract in the posterior subcapsular zone with pigment dispersal on lens and cornea contributing to the visual loss. Each patient had a full work up and was under constant medical supervision at our uvea clinic. Every patient was given a choice of surgery or laser but all the

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first 15 cases opted for an initial laser procedure after having been explained the possible complications and risks involved with such a procedure.

The mean age of 15 patients was 31.80 ± 9.52 years. The mean pre-laser IOP was 22.61 mm Hg while the average post-laser IOP was 17.33 ± 3.59 mm Hg at 4 weeks followup. The average pre-laser pupillary size was 3.6 ± 1.0 mm while the average post-laser pupillary size was 5.06 ± 1.50 mm (p<0.001). An average of 45.93 ± 14.31 shots were used. More than 2 line increase in visual acuity occurred in 6 eyes (40%), while no eye had a loss of best corrected acuity. The complications included hemorrhage (15/15), mild hyphema (7/15) and mild to moderate uveitis in all 15 patients. IOP spikes were less than 25 mmHg in all patients treated.

Iridolenticular adhesions with totally pharmacologically non-dilating pupil are not an uncommon entity in ophthalmic practice. It may result in iris bombe formation with peripheral anterior synechiae, and is commonly associated with cataract. It may interfere with vision, fundus visualization and evaluation for glaucoma becomes difficult. In all such cases, sectioning of adhesions should provide relief. Laser surgery being an outpatient procedure is obviously preferable. Our main purpose for trying synechiolysis in these cases was trying for visual improvement by increasing the pupillary diameter which could bypass the obstruction posterior subcapsular cataractous changes. The obvious additional advantage is that a number of these cases in time would go in for cataract surgery and performing an anterior capsulotomy is much easier along with aspiration of cortex without having to mechanically dilate the iris which could result in unwanted excess pigment dispersal and fibrinoid reaction postoperatively.

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The results clearly reveal that this procedure is no panacea as only 6 out of 15 cases achieved any gain in visual acuity along with dilatation of pupil. However, as most of these patients have chronic inflammation and cataract, surgery is also fraught with complications and any gain of visual acuity which can postpone surgery is very welcome to the patient. All cases had an associated micro hemorrhage along with pigment dispersal in anterior chamber. However, it was usually self limiting and one had to only apply some pressure with the contact lens to abolish the hemorrhage. Though hemorrhage and pigment may cause short-term deterioration of visualization, in none of our patients did it result in a long-term deterioration of vision. The elevation of intraocular pressure was definitely present but was easily controlled on single anti-glaucoma medication.

Thus overall no case showed any significant complication or any obvious lenticular damage on biomicrosocpy. Considering the advantages and relative safety, we recommend this procedure for routine use but by an experienced laser microsurgeon. Long-term results of visual benefit by this procedure must be reviewed in terms of further complications related to primary disease which can lead to enhancement of cataract, uveitis, retinal and optic nerve damage.

Modified Technique for Nd: YAG Laser Iridolenticular Synechiolysis

This technique differs from the above-mentioned technique of synechiolysis in the fact that instead of direct photodisruption, it utilizes the shock waves generated in aqueous to release the synechia. The aiming beam is focused at the center of the broad base synechia towards the side of iris. This is followed by slight anterior defocusing

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of the aiming beam. A power of 1-2 millijoules is used. Shock waves were generated in the aqueous and immediate lysis of the whole of the synechiae is observed, with mild pigment dispersion.

Post-laser treatment regimen includes topical 1 percent prednisolone acetate eye drops four time daily, 0.5 percent timolol maleate eye drops twice daily for four days and 1 percent tropicamide eye drop four times daily for one week.

In an initial technique (Nd:YAG iridolenticular synechiolysis) direct cutting of the synechiae with Nd:YAG laser, and the beam is directed at the synechia just at the junction of iris and lens was used. Though with Nd:YAG iridolenticular synechiolysis we did not observe any lens damage or clinically significant flare up of the inflammation but the theoretical possibility of lens damage does exist. Few cases where bleeding occurred, it was transient and could controlled easily and had no untoward effects. The new modified technique differs from the previous one in the fact that instead of direct photodisruption it utilizes the shock wave generated in aqueous to release the synechia. Thus this technique actually combines the virtues of YAG sweeping with lysis, therefore making lysis easier at points where a broad based synechiae are available. As the laser was aimed onto the iris at the center of the synechiae, possibility of lens damage is almost eliminated. Additionally, slight anterior defocusing of the aiming beam helps to eliminate the risk of iris damage. However, with misalignment and malfocusing of the laser, it may hit the crystalline lens. Accidental hitting of the lens with low-power Nd:YAG may not have an untoward effect, however, theoretically it may lead to lens damage and focal opacification of lens. This procedure also carries the theoretical risk of bleeding in presence of new vessels in the synechiae.

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Thus, this method appears to be a relatively safe technique for iridolenticular synechiolysis. Larger studies with longer follow-up are required to establish the complete safety and efficacy of this technique.

LASER SUTUROLYSIS

During trabeculectomy nylon sutures are applied to secure the scleral flap and to regulate the aqueous flow through the bleb. To avoid immediate postoperative hypotony and its complication especially in eyes with advanced glaucoma, tight sutures are preferred. However, if the intraocular pressure (IOP) is too high and anterior chamber is deep, laser suturolysis may be required.

Lens: The Hoskins lens is used for this purpose. However, in case this special lens is not available, then one can use the edge of a regular gonioscope or a four mirror gonioscope to press on the conjunctiva overlying the suture and thus helping in visualization.

Laser: Argon laser or frequency doubled Nd:YAG laser (532 nm) are the commonly used lasers.

Laser parameters: Spot size — 50 microns, power — 250 to 750 mW, duration — 0.1 second.

Technique

Patient is seated on the slit-lamp. Conjunctival sac is anesthetized with 0.5 percent proparacaine / 4 percent xylocaine. In case the conjunctiva is hyperemic and congested, it is a good option to decongest the same using the phenylepherine eye drops (10%), instilled two to three times at 10 minutes interval. Hoskins lens is applied over the bleb area. It helps to visualize the underlying suture and also protects the conjunctiva from thermal injury. Laser

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spot is applied over the visible suture arm. If there is accompanying subconjunctival hemorrhage or pigmentation, krypton red laser (600 nm) may be used in order to avoid damage to the conjunctiva as melanin, hemoglobin and nylon suture have absorption spectrum near 532 nm. Following suturolysis mild bleb massage is given and immediate lowering of IOP with mild shallowing of anterior chamber and bleb formation is noted.

Suturolysis is generally performed within 2 weeks of surgery but can be performed up to 4 weeks, if adjunctive anti-fibrotic agents have been used. This technique is not effective at a later stage when the fibrosis has already set in.

LASER-ASSISTED BLEB REMODELING

Large overhanging bleb is a well documented complication of trabeculectomy, especially if Mitomycin C has been used. It can be associated with complications like over-filtration, hypotony and extremely large blebs can result in foreign body sensation, discomfort, decreases in visual acuity due to astigmatism, and dellen formation. These blebs are also predisposed to late onset leaks, blebitis, and endophthalmitis. Various therapeutic modalities like surgical repair, injection of autologous blood, cryotherapy, have been employed for treating this problem.

The presumed mechanism through which the laser treatment works is based on the fact laser generates thermal energy which results in tissue protein denaturation. This causes shrinkage of the collagen tissue, and as the laser beam selectively affects the inner surface of the bleb leading to inflammation and fibrosis without damaging the overlying conjunctiva, this results in remodeling or shrinkage of the bleb.

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Laser: Argon laser, frequency doubled Nd:YAG laser.

Laser parameters: 300-500 mW power, 500 microns size and 0.1 seconds duration.

Technique

The eye is anesthetized with one drop of 0.5 percent proparacaine, and the patient is seated in front of the slitlamp mounted with laser. Heat absorption by epithelial surface can be promoted by application of a dye. The bleb surface is painted with gentian violet using sterile cotton tipped applicator. Another option is to use vital dyes like rose bengal and methylene blue dye, which require light epithelial abrasion. 25-50 spots are applied on the surface of bleb in the area of maximum height. An immediate shrinkage in the elevation of bleb is noticed.

At follow-up apart from IOP monitoring, the bleb area is examined for any evident leak. Repeat treatments may be performed if required.

Complications include bleb failure due to over treatment and iatrogenic perforation leading to wound leak. Bleb leaks due to laser induced perforation occur with over treatment, especially with thin and transparent blebs.

Nd:YAG GONIOPUNCTURE

Goniopuncture of the trabeculo-Descemet’s membrane complex is performed in cases with operated nonpenetrating deep sclerectomy (NPDS), where postoperative bleb functioning is inefficient and the IOP remains high. The laser treatment is performed with Q-switched Nd:YAG laser to puncture the Descemet’s membrane and convert the NPDS into a penetrating procedure. This significantly enhances the success of NPDS.

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Lens: Lasag 15 gonioscopy contact lens (CGA1).

Laser settings: Energy 2 to 4 mJ.

Studies have shown that goniopunctures decreases the mean IOP with an immediate success rate of 70-85 percent. Apart from the eyes with operated NPDS with insufficient IOP control. Nd:YAG goniopuncture may also be performed as primary procedure along with deep sclerectomy in eyes with Sturge-Weber syndrome. This is a two staged technique described by Hara et al. In Stage 1, under conjunctival and thin scleral flaps, the deep (4 × 2 mm) scleral block containing the outer wall of Schlemm’s canal is removed. Stage 2, the puncturing of the remaining trabeculum with Q-switched Nd:YAG laser, is performed the next day. This helps to avoid hemorrhagic choroidal detachment which frequently occur in these eyes following a penetrating filtering surgery.

Complications

Iris synechia is a potential complication that may cause elevated IOP after laser goniopuncture in patients having NPDS. Occasionally a spontaneous iris prolapse may also occur leading to IOP elevation.

ERBIUM-YAG LASER-ASSISTED DEEP SCLERECTOMY

Lasers have been increasingly used for scleral ablation during NPDS. Laser decreases the mechanical or thermal damage resulting in decreased scarring. Both excimer laser and Erbium:YAG laser have been used for this purpose. Theoretically speaking Erbium:YAG laser (2940 nm/11 mJ, 7 Hz) provides extra safety by eliminating the possibility of ultraviolet light related cyto-toxicity and retinal toxicity.