7.1.4.1 Level 1: Iris and Pupillary Block

The competing forces of the iris muscles, the sphincter and dilator of the pupil, create a vector force at the margin of the pupil that is directed posteriorly onto the anterior surface of the lens. This occurs when the pupil is of medium width. Remember that pseudoexfoliation material is rubbed off the surface of the lens in the midperiphery of the lens surface giving the appearance of a doughnut.

The pupillary margin blocks the ßow of the aqueous humor from the posterior to the anterior chamber. Subsequently the iris, predominantly in the peripheral, thinner part will bow forward. The lens acts like a ball valve and closes the ßow of the aqueous humor through the pupil. Iris tissue will form contacts with the trabecular meshwork or SchwalbeÕs ring (ITC). Some of the contacts will release by themselves (pupil constricts, ÒintermittentÓ angle closure), and some will change to peripheral anterior synechiae (Fig. 7.5).

Note: only a minority of patients experience subjective symptoms such as pain, red eye or halos when looking into light sources. The majority show no symptoms.

If posterior synechiae (i.e. between iris and lens) have led to a forward bowing of the iris, we speak about Òiris bombataÓ or Òiris bombŽÓ.

Predisposing factors for a pupillary block in an anatomically predisposed eye are, for example: diagnostic mydriasis, watching TV or movies in a cinema with dim light, emotional situations with high adrenergic output, drugs (e.g. antidepressant serotonin uptake inhibitors).

New Insights

Why does not everybody with a narrow angle develop ITC or synechiae or develop an angle closure? ÒThe iris is like a spongeÓ, wrote Quigley et al. in 2000. They observed the dynamics of the iris change during dilation in the dark and constriction in bright light by means of AC-OCT and found that the iris usually gets smaller upon dilation due to volume loss and enlarges as the pupil narrows. The iris acts like a spongeÑwater moves in and out of it. People with narrow angles loose less iris volume upon dilation.

7.1.4.2 Level 2: Ciliary Body: Plateau Iris

Plateau iris conÞguration is a gonioscopic Þnding, where at least one of the following items should be determined (Fig. 7.6)

¥Thick peripheral iris roll.

¥Anterior insertion of the iris (anterior to the scleral spur).

¥Anterior insertion and rotation of the ciliary body so that the ciliary processes are visible on gonioscopy. There is no or almost no ciliary sulcus. UBM and/or AS-OCT provide an additional insight into the anatomical structures behind the iris.

¥Very steep peripheral iris with normal depth of the anterior chamber centrally. The angle is narrow (<10¡) or closed for at least 180¡. The central iris is ßat (Fig. 7.7).

¥ÒDouble hump signÓ or Òsinus wave signÓ in indentation gonioscopy. A peripheral hump of the iris is seen by the anteriorly rotated ciliary body, and a more centrally located second hump of the iris is formed by the shoulder of the lens (Fig. 7.8).

Fig. 7.7 Flat iris with normal depth of the anterior chamber, but very steep drop-off of the iris into the chamber angle. The scleral spur and a heavily pigmented trabecular meshwork are visible

To release the pupillary block a peripheral iridotomy is recommended. The majority will be healed.

In eyes without pupillary block and/or iris tissue very close to the trabecular meshwork, an increase in the IOP will result after dilation of the pupil despite a patent iridotomy and the diagnosis will

change to plateau iris syndrome. This will lead to peripheral anterior synechiae and closure of the angle. Sometimes chronic use of pilocarpine 1Ð0.1% is indicated.

The next step in treatment would be an argon laser peripheral iridoplasty. Argon laser burns are placed circumferentially on the peripheral parts of the iris to shrink the tissue and ßatten the periphery of the iris. The pupil is constricted with pilocarpine 1% preoperatively. Inform the patient before treatment that the procedure may be painful and that the pupil might remain larger than it was before the laser treatment. Use a contact lens (Wise, Abraham), a spot size of 500 mm, a pulse duration of 0.2Ð0.5 s, an energy of 200Ð400 mW (depending on the color of the iris), and Þve burns per quadrant. Postoperatively nonsteroidal antiinßammatory eye drops are given (see Chap. 9, Sect. 9.1.3)

7.1.4.3Level 3: Lens

An increase in the thickness of the lens (intumescent cataract, nuclear cataract, ÒphacomorphicÓ glaucoma) or a change in the position of the lens (subluxation after trauma or in pseudoexfoliation due to weak zonules) may lead to a forward pushing of the iris and closure of the chamber angle. Treatment is cataract surgery, which is not always simple in these eyes.

7.1.4.4Level 4: Retrolenticular Aqueous

Misdirection

This troublesome (for the patient as well as the surgeon) reaction of an eye after trabeculectomy or cataract surgery needs special care. It is also called Òmalignant glaucomaÓ, but this term should be avoided so as not to upset or confuse the patient with the association to cancer.

In an eye with a recent trabeculectomy, a very shallow anterior chamber despite an open iridectomy, no choroidal effusion and a relatively high IOP (between 15 and 20 mmHg or more; Figs. 7.9 and 7.10) should arouse the suspicion of aqueous misdirection. Usually eyes with a shallow anterior chamber postoperatively have a very low IOP (0Ð5 mmHg). The main reasons are a ciliolenticular block (Fig. 7.11) and an increase in volume in the

Fig. 7.9 Eye on the Þrst day after Þltration surgery. The anterior chamber is very shallow centrally and almost gone in the periphery. The peripheral iridectomy is patent, and running limbal suture of conjunctiva/TenonÕs capsule is visible (IOP 22 mmHg)

Fig. 7.10 Same eye as shown in Fig. 7.9 (slit beam examination) with a very shallow anterior chamber, but without the lens touching the corneal endothelium

choroids. A ciliolenticular block is a blockage between a thick, anterior rotated ciliary muscle and its processes and the equator of the lens, preventing the aqueous humor from ßowing anteriorly.