Fig. 15-4  Anterior segment ocular coherent tomography 180° image of narrow angles pre iridotomy.

(Courtesy of Mingguang He, MD.)

surgery;69,100–102 anomalous anatomical positioning of the ciliary processes in plateau iris,103,104 etc. Other instruments extend our

abilities to meticulously assess the anterior chamber depth, such

as the scanning peripheral anterior chamber (SPAC) depth analyzer105,106 and the Pentacam (Oculus Instruments) device incor-

porating Scheimpflug photography.107

As a result of the revolutionary technologies of the UBM and AS-OCT studies in particular, specific mechanisms and parameters for comprehending PAC disease are being elaborated.When combined with the classical literature based on clinical observations of subtle variations in disease presentations, a fuller picture of the angle-closure glaucomas results.

(A)

(B)

Classification by mechanisms in the anterior segment

We classify the primary angle-closure mechanisms based on three site-specific disturbances in the anterior segment. We group these mechanisms because they share important characteristics in common: (1) all three can, with clinical input, be discriminated by anterior segment imaging; (2) they clinically manifest under similar circumstances, clustering closely in the differential diagnosis of causes of PACG; and (3) they differentially respond to laser iridotomy, which helps discriminate among the underlying mechanisms (Fig. 15.5).* The three pathophysical mechanisms grouped in the consideration of PACG are:

1.pupillary block glaucoma

2.plateau iris: configuration and syndrome (ciliary body anomalies)

3.phacomorphic glaucoma (lens-induced obstruction).

Conditions involving forces involving the mid or posterior segments of the eye, such as ciliary block (malignant) glaucoma or cilio-choroidal detachments, are discussed in the following chapter.

*Although ciliary block (‘malignant’) glaucoma has been included among the mechanisms at play in the primary angle-closure classification,20 we respectfully dissent and prefer to include it among the secondary angle-closure glaucomas. This is because of the rarity of ciliary block glaucoma, because its commonest presentation is postoperative, and because the target anatomical sites of vitreal– hyaloid and zonular–lens interface are not usually clarified by UBM studies (as are the three other mechanisms of PACG).

Fig. 15-5  Schematic view of three different mechanisms of PACG.

(A) Pupillary block with shallow anterior chamber, both centrally and peripherally, and iris bombé. Posterior chamber is enlarged. (B) Plateau iris configuration with relatively deep central anterior chamber and shallow peripheral anterior chamber. The plane of the iris is flat until near its insertion, where it takes a sharp, angled turn. (C) Anterior displacement of the lens (phacomorphic) with shallow anterior chamber, both centrally and peripherally: the iris is draped over the lens, and the posterior chamber is compressed.

1. PUPILLARY BLOCK GLAUCOMA

Pupillary block is the fundamental mechanism underlying the spectrum of PAC disease. Its pathophysiology involves: (1) lens– iris apposition at the pupil, with resultant bowing forward of the peripheral iris as aqueous pressure builds up in the posterior chamber; and (2) an anatomically predisposed eye that allows the anterior displaced peripheral iris to occlude the trabecular meshwork. The commonplace distinction between an acute attack and chronic disease remains important for clinical management decisions.