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

12 Step by Step Minimally Invasive Glaucoma Surgery

Fig. 2.1: Slit lamp

If the patient has already had an attack of acute congestive glaucoma, first medical treatment is carried out (Box 2.1). This will reduce the corneal edema. In addition, the pupil can be easily constricted by pilocarpine. The steroid drops should also be instilled if iritis is present for a couple of days before proceeding for laser iridotomy. If acute attack does not abort, one can proceed with iridotomy.

So, preoperatively pilocarpine eye drops are instilled one hour prior to constrict the pupil to maximum.

Apraclonidine 1 percent is instilled one hour prior to the procedure to prevent postoperative pressure spike.12 Topical proparacaine 0.5 percent is instilled just before the procedure to anesthetize the conjunctiva and cornea.

THE SELECTION OF IRIDOTOMY SITE

It is usually superonasal between the peripheral and middle third of iris. The reasons for this are (a) the superior

YAG Laser Iridotomy 13

Box 2.1

We follow the New York Eye and Ear Infirmary approach1 to acute angle closure glaucoma, which is as follow:

1.Careful history of symptoms relating to intermittent angle closure attacks, attacks in the other eye, use of prescription or nonprescription drugs which may precipitate attacks, and type of activity precipitating the attack.

2.Examination of the affected eye and other eye with attention to central and peripheral anterior chamber depth as well as shape of the peripheral iris.

3.Administration of oral isosorbide, acetazolamide as aqueous suppressants, and even intravenous mannitol at our place.

4.The patient lies supine to permit the lens to fall posteriorly with vitreous dehydration.

5.The eye is reassessed after 1 hour. IOP is usually decreased, but the angle usually remains appostionally closed. One drop of 2 or 4 percent pilocarpine is given and patient is reexamined 30 minutes later.

6.If IOP is reduced and the angle is open, the patient may be treated medically with topical low dose pilocarpine, aqueous suppressants and steroids, until the eye quiets and laser iridotomy may be performed.

7.If IOP is unchanged or elevated and angle remains closed. Lens related angle closure should be suspected, further pilocarpine is withheld and the attack broken by argon laser

peripheral iridoplasty.

Peripheral iridoplasty does not eliminate pupillary block and is not a substitute for laser iridotomy, which must be performed as soon as the eye is quiet. However, even in eyes with extensive synechial closure, IOP is lowered sufficiently for a few days for the inflammation to resolve. Peripheral iridoplasty is much safer than attempting surgical iridectomy on an inflammed eye with elevated IOP. The risks of intraoperative surgery are avoided and even if malignant glaucoma is present the angle remains open long enough for inflammation to clear. Peripheral iridoplasty is highly effective in ameliorating attacks of angle closure glaucoma in Asian eyes.

1.Kramer P, Ritch R. The treatment of angle closure glaucoma revisited (editorial). Ann Ophthalmol 1984;16:1101-03.

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site remains covered by the lid (b) the nasal side remains away from the macula preventing foveal burn (c) the junction of middle and peripheral third helps in easy penetration. (d) crypt is selected because here the iris is thinnest and easy to penetrate (e) the iris should be examined for any strands. If present, they should be avoided, as they are difficult to penetrate. (f) the lower site is chosen in silicon filled eye because the silicon oil floats and can go to upper site and block the iridotomy.

LASERS USED

Several lasers can be used. But the commonly used lasers are Nd: YAG and argon. We will describe here the YAG laser iridotomy.

Nd: YAG Laser Iridotomy

This is most frequently applied method for laser iridotomy. There are several advantages of using YAG laser. This produces extremely high energy, which acts by mechanical disruption. When compared to argon laser, it does not require pigment for absorption for its thermal effect. The spot size is usually fixed to one size (50-75 um) in lasers from different companies. The pulse duration is also fixed for each instrument. The energy levels can be varied. Depending on the color of iris the required energy levels for penetration can be between 5-15 mJ. More energy is required for brown iris. The pulses can be between 1 to 3, which depends largely on the choice of surgeon. YAG laser penetrates simultaneously the iris stroma and pigment epithelium. The only problem with YAG laser iridotomy is bleeding from iris capillaries, which should be avoided if visible.

YAG Laser Iridotomy 15

After selecting the site and applying the Abraham’s lens the laser shot is placed at the iris surface after properly focusing the laser beam. Usually one shot is sufficient for blue iris, but at times more than may be required. In brown iris more shots may be needed and the required energy levels may be also be high. The created opening should not be less than 150-200 um,13 otherwise there are chances of its closure. If some difficulty is experienced in enlarging the hole another site may be chosen. Two sites, even if small, are less likely to close (Fig. 2.1).

Argon and YAG Laser Combined

My technique is first using low intensity large size 200 um argon laser burns to create a crator and then utilizing single pulse low intensity shot of Argon laser also coagulates the capillaries thus reducing the chances of iris bleed.14

POST-LASER TREATMENT

•Steroid drops are given to prevent mild iritis.

•Pilocarpine eye drops are advised to keep the pupil constricted so that the opening remains patent.

COMPLICATIONS

1.Common complications

—Transient IOP rise

—Iridocyclitis

2.Others

—Closure of iridotomy

—Hyphema

—Corneal damage cataract formation

3.Rare complications

—Retinal burns

—Malignant glaucoma

16Step by Step Minimally Invasive Glaucoma Surgery

—Monoocular blurring

—Endothelial cell loss

—Posterior synechia

Common Complications

Transient Rise of IOP

This is commonest complication. The rise of IOP occurs due to decrease in aqueous outflow facility, although aqueous outflow facility gets reduced.15 Other studies suggest that it could be because of release of prostaglandins16-18 and prostaglandin like substances into the aqueous,19 which occurs due to breakdown in the blood aqueous barrier. The blood plasma and fibrin are also released, which may also block the iridotomy site or angle leading to IOP rise. For preventing this rise 1 percent apraclonidine eye drops should be instilled one hour prior to laser iridotomy and also immediately after the procedure.

Iridocyclitis

As a reaction to YAG laser insult a mild iritis can occur.20 This can easily be managed by giving steroid drops for 3-5 days. However, rarely severe iridocyclitis,21 cystoid macular edema22 and even endophthalmitis23 have been reported.

Other Communications

Hyphema

If the laser beam hits iris capillaries, the blood may be seen leaking from them.8,9 This bleeding can be easily managed by applying pressure with the help of contact lens. If

YAG Laser Iridotomy 17

previous to the YAG laser, Argon laser is utilized the chances of bleeding are reduced as it coagulates the capillaries.

Closure of Iridotomy

The size of iridotomy should be about 150-200 um,13 because small iridotomy may close due to pigment granules and debris release from the iris by YAG laser disruption. For keeping the iridotomy patent pilocarpine should be instilled postoperatively. If it seems to the clinician that confirmation of patency is required, a provocative mydriatic test should be done after stopping pilocarpine drops. Although most of the time a slit-lamp evaluation done under high magnification confirms the patency, wherein anterior capsule’s visibility suffices. Long-term patency rates of YAG laser iridotomy are very good in dark Asian irides in line with other studies in white and AfroCaribbean eyes.24-26

Cataract Formation

The incidence of cataract formation is much less with YAG laser than with argon laser iridotomy. It is said that they are non-progressive. Laser peripheral iridotomy disrupts the natural flow of aqueous in the eye and results in significant increase in lens-iris contact.27 Theoretically, this may predispose to a more rapid development of cataract since less aqueous is in contact with the lens epithelium. Several studies have attempted to look at this issue, but follow-up has been short, no lens grading system was used, and no acceptable control groups were studied.28-29 Focal lenticular opacities seen after argon laser peripheral iridotomy are said not to progress, but once again, followup has been short in published reports.

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Rare Complications

Retinal Burns

Retinal burns may occur due to YAG laser iridotomy since the laser beam may hit the retina. If the precautions mentioned previously are not taken it may also hit the fovea and cause sudden diminution of vision. The best way of avoiding this complication is by choosing the superonasal site. Some authorities believe that using the Abraham lens also prevents damage to fovea.

Malignant Glaucoma

This is also rarely described complication and has been reported in one eye and both eyes too.

Endothelial Cell Loss

One study documenteda higher rate of endothelial cell loss after argon laser peripheral iridotomy than after YAG laser peripheral iridotomy.24

Posterior Synechia

Another potential complication of laser peripheral iridotomy is the development of posterior synechiae following laser iridotomy.25 Posterior synechiae can both limit vision in dim environments and make later cataract surgery more challenging.

Failure of Iridotomy

Several studies demonstrate a relation between the extent of angle closure by PAS and failure of iridotomy to control IOP and progression of glaucoma.30-32 Iridectomy or

YAG Laser Iridotomy 19

iridotomyis less effective in eyes with glaucomatous visual field loss and further surgical or medical treatment is often required to control IOP.33,34

REFERENCES

1.Meyer-Schwickerath G. Erfahrungen mit der lichokoagulation der Netzhaut und der iris. Doc Ophthalmol 1956;10:91.

2.Hogan MF, Schwartz A. Experimental photocoagulation of the iris of guinea pigs. Am J Ophthalmol 1960;49:629.

3.Perkins AS. Laser iridotomy for secondary glaucoma. Trans Ophthalmol UK 1971;91:777.

4.Khuri CH. Argon laser iridectomies. Am J Ophthalmol 1973;76:490.

5.Anderson DR, Forster RK, Lewis M. Laser iridotomy for aphakic pupillary block. Arch Ophthlol 1975;93:343.

6.Yassur Y, Melamed S, Cohen S, Ben-Sira I. Laser iridotomy in closed angle glaucoma. Arch Opthalmol 1979;97:1920.

7.Pollack IP. Use of argon lasr to produce iridotomies. Ophthalmic Surg 1980;11:506.

8.Latina MA, Puliafito CA, Steinert RR, Epstein DL. Experimental iridotomy with a Q-switched Nd: YAG laser. Arch Ophthalmol 1984;102:1211.

9.Klapper RM. Q-switched Nd: YAG laser iridotomy. Ophthalmology 1984;91:1017.

10.Vernon SA, Cheng H. Freeze frame analysis on high-speed cinematography of Nd: YAG laser explosions in ocular tissues. Br J Ophthalmol 1986;70:321.

11.Abraham RK. Procedure for outpatient argon laser iridectomies for angle closure glaucoma. Int Ophthalmol Clin 1976;16:1.

12.Krupin T, Stank T, Feitl ME. Apraclonidine pretreatment decreases the acute intraocular pressure rise after laser trabeculoplasty or iridotomy. J Glau 1992;1:79.

13.Fleck BW. How large must an iridotomy be? Br J Ophthalmol 1990;74:583.

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14.Del-Priore LV, Robin AL, Pollack IP. Neodymium: YAG and argon laser iridotomy. Long-term follow-up in a prospective, randomized clinical trial. Ophthalmology 1988;95:1207-11.

15.Wetzel W. Ocular aqueous humour dynamics after photodisruptive laser surgery. Ophthalmics Surg 1994;25: 298.

16.Sugiyama K, Kitazawa Y, Kawai K, Enya T. Biphasic intraocular pressure response to Q-switched Nd: YAG laser irradiation of the iris and the apparent mediatory role of prostaglandins. Exp Eye Res 1990;51:531.

17.Gailitis R, Peyman G A, Pulido J, et al. Prostaglandin release following Nd: YAG iridotomy in rabbits. Ophthalmic Surg 1986;17:467.

18.Joo CK, Kim JH. Prostaglandin E in rabbit aqueous humour after Nd: YAG laser photodisruption of iris and the effect of topical indomethacin pretreatment. 1992;33: 1685.

19.Weinreb RN, Weaver D, Mitchell MD. Prostanoids in rabbit aqueous humour: effect of the laser photocoagulation of the iris. Invest Ophthalmol Vis Sci 1985;26:1087.

20.Schrems W, van Dorp HP, Wendel M, Krieglstein GK. The effect of YAG laser iridotomy on the blood aqueous barrier in the rabbit. Graefes Arch Clin Exp Ophthalmol 1984;221: 179.

21.Cohen JS, Biblar L, Tucker D. Hypopyon following laser iridotomy. Ophthalmic Surg 1984;15:604.

22.Margo CE, Lessner A, Goldey SH, Sherwood M. Lensinduced endophthalmitis after Nd: YAG laser iridotomy. Am J Ophthalmol 1992;113:97.

23.Choplin NT, Bene CH. Cystoid macular oedema following laser iridotomy. Ann Ophthalmol 1983;15:172.

24.Schwartz LW, Moster MR, Spaeth GL, et al. NeodymiumYAG laser iridectomies in glaucoma associated with closed or occludable angles. Am J Ophthalmol 1986;102:41-44.

25.Canning CR, Capon MRC, Sherrard ES, et al. Neodymium: YAG laser iridotomies short-term comparison with