Ординатура / Офтальмология / Английские материалы / Mechanisms of the Glaucomas_Shields, Tombran-Tink, Barnstable_2008

Fig. 6. Peripheral anterior synechia in eye with anterior uveitis and iris bombe’ on gonioscopy (provided by Dr. S. Sawaguchi).

Angle closure due to iris bombe’ with ocular hypertension should be treated with LPI. However, this may be different if there is corneal edema or active uveitis, in which case steroid and anti-glaucoma medication may be required prior to LPI. In some cases in which LPI cannot be successfully performed, IPI may be required.

REFERENCES

1.Yamamoto T, et al. Tajimi Study Report 2. Prevalence of primary angle closure and secondary glaucoma in a Japanese population. Ophthalmology 112; 1661–1669, 2005.

2.Sasaki H, et al. Comparison of latanoprost monotherapy and combined therapy of 0.5 timolol and 1% dorzolamide in chronic primary angle-closure glaucoma (CACG) in Japanese patients. J Ocular Pharmacol Ther 21; 483–489, 2005.

3.Aung T, et al. Acute primary angle closure: long term intraocular pressure outcome in Asia eyes. Am J Ophthalmol 131; 7–12, 2001.

4.Jacobi PC, et al. Primary phacoemulsification and intraocular lens implantation for acute angle-closure glaucoma. Ophthalmology 109; 1597–1603, 2002.

Anterior segment optical coherence tomography (OCT) is a recently developed method that allows for objective and quantitative imaging of anterior segment structures and angle configuration (10–12). Advantages over UBM include non-contact methodology with consequent reduction of patient discomfort and risk and the ability to image the eye in the sitting position. However, because of its reliance on light rather than sound waves, anterior segment OCT cannot image structures posterior to the pigment epithelium of the iris and ciliary body.

ANGLE CLOSURE ORIGINATING AT THE LEVEL

OF THE CILIARY BODY

Plateau Iris

Angle closure at the level of the ciliary body is caused mainly by plateau iris, first described by Tornquist in 1958 (13). Plateau iris configuration denotes an angle appearance in which the iris root sharply angulates forward and then centrally. The iris surface appears flat (hence the term “plateau”), and the central anterior chamber is of relatively normal depth. Primary plateau iris is associated with a large or anteriorly positioned ciliary body that physically supports the iris root against the trabecular meshwork (see Fig. 2A) (2,14). This can be vividly appreciated during dynamic indentation gonioscopy. While corneal indentation in eyes with pupillary block results in posterior movement of the mid-peripheral iris, in plateau configuration the ciliary processes prevent this movement. Thus, looking from the pupil toward the angle, the slit beam follows the convex curvature of the iris to its deepest point at the equator of the lens, and then rises again over the ciliary process before sharply dropping peripherally. This phenomenon is known as the “double hump” sign (see Fig. 3) (14). This anatomic configuration also prevents posterior fall of the iris following iridotomy and can persist even after lens extraction (15).

The term plateau iris syndrome was coined by Wand et al. in 1977 (3). It refers to the development of angle closure, either spontaneously or after pupillary dilatation, in an eye with plateau iris configuration despite the presence of a patent iridotomy (see Fig. 2B). When performing gonioscopy in this situation, the experienced gonioscopist can appreciate that greater force is needed to open the appositionally closed angle than in pupillary block, because the ciliary processes, rather than aqueous, must be displaced.

It is very useful to differentiate clinically the commonly observed configuration from the less common syndrome. The syndrome entails angle closure and therefore necessitates consideration for further treatment, whereas eyes with plateau configuration only require follow-up. In eyes with plateau iris syndrome, whether or not intraocular pressure (IOP) rises during angle closure depends on the level of iris–corneal apposition with respect to the angle structures or the “height” to which the plateau rises (16). If the angle closes completely to the upper trabecular meshwork or Schwalbe’s line, the IOP will rise, whereas if it closes partially, leaving the upper portion of the filtering meshwork open, it will not. The latter situation is far more common and is clinically significant, because these patients may develop peripheral anterior synechiae (PAS) years after a successful iridotomy produces what appears to be a well-opened angle.

C

C

IR

CB

(c)

C

*CB

Fig. 2. (A) Plateau iris configuration. Arrows indicate closed angle with irido-corneal touch. (B) Plateau iris following laser peripheral iridotomy. Arrows indicate persistent closed angle with irido-corneal touch. (C) Plateau iris following argon laser peripheral iridoplasty. The angle is open. Arrows indicate iris thinning at the site of iridoplasty burn. Asterisk indicates scleral spur. C, cornea; CB, large anterior ciliary body; I, iris; IR, patent iridotomy.

Although infrequent, some patients with plateau iris syndrome may develop acuteangle closure (3,17–19). This can occur in an iridotomized eye. Alternatively, appositional angle closure may persist following laser iridotomy for acute-angle closure attack.

Patients with plateau iris tend to be female, middle age (30s to 50s), and less hyperopic than those with relative pupillary block and often have a family history of angle-closure glaucoma. In a series of 67 patients with angle closure developing at age 40 or younger, 35 had plateau iris syndrome (20). One of these had high axial myopia,

Fig. 3. Gonioscopic double hump sign.

a finding that should not rule out angle closure and thus routine gonioscopy (21). With age, progressive enlargement of the lens can cause further narrowing of the angle. Therefore, periodic gonioscopy is indicated. Another result of lens enlargement is a greater component of pupillary block, which causes the iris to be less “plateau” and more convex. This clinical scenario exemplifies how angle closure can be multifactorial in a single eye.

The goal of treatment of eyes with iridocorneal apposition secondary to plateau iris syndrome is mainly to prevent the development of PAS and chronic angle closure and also to prevent those few cases of acute-angle closure. In addition, the goal is to prevent intermittent elevated IOP occurring only in the dark. As some element of pupillary block usually cannot be ruled out in these eyes, iridotomy might result in an open angle and should be the first intervention performed in most, if not all, cases. If persistent iridotrabecular apposition is present despite a patent iridotomy (see Fig. 2B), argon laser peripheral iridoplasty (ALPI) is indicated. This procedure involves the application of contraction burns of low energy, large spot size, and long duration to the peripheral iris. This compacts and contracts the peripheral iris stroma, creating a space between the anterior iris surface and the trabecular meshwork, thus physically opening the angle (see Fig. 2C) (22–24).

Long-term results of ALPI in plateau iris syndrome are encouraging (25). In 20 of 23 eyes (87.0%), the angle remained open throughout the entire follow-up period of 72–188 months after a single treatment. In three eyes, there was gradual reclosure of the angle 5–9 years after initial ALPI, but these were readily reopened and maintained open by a single repeat treatment. No filtration surgery was necessary in any eye during follow-up. There was no documented progression of PAS in any eye.

Pilocarpine can be used to thin the iris and widen the angle. Its effect can be visualized by repeating gonioscopy shortly after application. Although this is a possible

C

IC I

Fig. 4. Iridociliary cyst. Arrows indicate closed angle. C, cornea; IC, iridociliary cyst; I, iris.

therapy, we think that achieving long-term non-occludability of the angle with a single treatment of ALPI is preferable, as it produces a more stable angle and avoids the wellknown side effects of long-term use of pilocarpine, especially in younger individuals. If used, the lowest effective concentration of pilocarpine should be chosen, even if not readily available commercially, and consideration should be given to using it only at night.

Pseudo-plateau Iris

Secondary or pseudo-plateau iris is caused by lesions that cause enlargement of the ciliary body, such as iris or ciliary body cysts. The clinical appearance of the iris and angle is similar to that which is seen in plateau iris syndrome, with the exception that these lesions typically involve only part of the angle circumference, even when they are multiple (see Fig. 4) (20,26,27).

Solid lesions of the ciliary body, such as infiltration by tumor or inflammation, can also produce a pseudo-plateau iris configuration, especially when there is homogenous full-circumference infiltration. Although these lesions can sometimes be seen through the well-dilated pupil, UBM demonstrates the discrete lesion and is therefore extremely helpful in making a definite diagnosis.

ANGLE CLOSURE ORIGINATING AT THE LEVEL OF THE LENS

Definition

When the lens physically compresses the iris and ciliary body against the trabecular meshwork, lens-related angle closure is said to occur (see Fig. 5). This may also be termed “phacomorphic” angle closure or glaucoma, to distinguish it from open-angle, lens-related increase in IOP such as “phacolytic” or “phacoanaphylactic” glaucoma.

C

I

L

Fig. 5. Phacomorphic angle closure. There is extensive irido-corneal apposition, closed angle, and shallow chamber. Arrows indicate irido-corneal touch. C, cornea; I, iris; L, cataractous lens.

Angle Closure Secondary to Lens Enlargement

Most commonly, this occurs secondary to progressive age-related increases in lens size. In these eyes, a component of pupillary block may be present and may also increase with progressive lens thickening. Conceivably, when a large lens narrows the angle, a smaller degree of peripheral iris bowing is required to close the angle. Early in the management of these cases, pupillary block may be easily relieved with laser iridotomy, allowing better evaluation of the remaining lens-induced component. However, the clinician may be able to assess the lens-induced component prior to iridotomy and thus advise the patient of the expected result of iridotomy. When indentation gonioscopy is performed in an eye with mainly pupillary block, the iris convexity is easily flattened and the irido-trabecular apposition relieved, as the force opposing corneal indentation originates in aqueous trapped behind the iris and this aqueous is easily displaced by corneal indentation. However, in a lens-induced mechanism, the lens physically supports the iris. Hence, the iris can be seen to closely drape over the lens in a volcanolike configuration, with the pupil as the crater (see Fig. 6). The experienced examiner can clearly appreciate that much greater force is needed during indentation to force aqueous into the angle and open it, as the lens itself must be displaced posteriorly.

Angle Closure Secondary to Forward Lens Movement

Lens-related angle closure may be caused by an abnormality of lens position rather than size. The lens may move anteriorly when there is weakened zonular support. Acute elevation of IOP may be caused by severe subluxation or dislocation of the lens (which may be accompanied by pupillary block), but a more subtle and chronic lensinduced angle closure may also occur. Associated conditions include pseudoexfoliation syndrome (28,29), Weill–Marchesani syndrome (21,30,31), blunt trauma (32), and Marfan’s syndrome (21,33).

Fig. 6. “Volcano-crater” iris configuration during indentation gonioscopy in an eye with phacomorphic angle closure.

Swelling of the lens may cause acute-angle closure with markedly increased IOP. Again, in these cases, pupillary block may be an associated factor and LPI may help to control IOP, at least initially (34,35).

Treatment

The identification of a phacomorphic component to angle closure has specific implications for treatment. Pilocarpine, which intuitively is thought to pull the iris away from the angle, should be used with extreme caution. By contracting the longitudinal ciliary muscle, it causes the lens to become thicker axially and also to move anteriorly, even in elderly patients (36,37). We have described a highly myopic patient in which pilocarpine caused reversible angle closure (21), and acute rise in IOP after use of pilocarpine has also been described in patients with Weill–Marchesani syndrome (38,39). Thus, if pilocarpine is used in these eyes, IOP and angle width should be assessed after a single application, and if a paradoxical reaction of angle narrowing and/or increase in IOP are observed, pilocarpine should be discontinued. In cases for which surgery is not immediately planned, cyloplegics (preferably cyclopentolate) may bring about angle widening.

When lens-related appositional angle closure persists after laser iridotomy, further treatment is necessary. When there is no visually significant lens opacification, ALPI may be performed and may cause widening of the angle but often needs to be repeated because of continued pressure from and growth of the lens (40). Lens extraction can lead to widening of the angle and lowering of IOP (41–49). If there is complete or nearcomplete PAS, ALPI or lens extraction is not expected to affect angle width or IOP. If there is increased IOP, uncontrolled by medications, trabeculectomy or combined cataract extraction and trabeculectomy are indicated. In cases where synechial closure