(A)

(B)

Fig. 5-4  (A) Plateau iris syndrome with anteriorly rotated ciliary process pressing peripheral iris forward toward the angle. (B) Following laser iridotomy there is virtually no change in either iris or angle configuration. (From Pavlin CJ, Foster FS: Ultrasound in biomicroscopy in glaucoma. In Ritch R, Shields MB, Krupin T, editors: The glaucomas, 2nd edn, St Louis, Mosby, 1996.)

the anterior chamber is deep, its convexity (or even bowing) in eyes

with a shallow anterior chamber, or its peripheral concavity in eyes with high myopia or signs of pigment dispersion.29,30 After assessing

the configuration of the peripheral iris, attention should be paid to the site of iris insertion – both its apparent and actual juncture in the angle. Indentation gonioscopy is particularly helpful in distinguishing iris–trabecular touch (apposition) from genuine adhesion. The level of iris insertion can be described in reference to structures within the angle recess – at the level of the upper trabecular meshwork and Schwalbe’s line; at the level of the filtering trabecular meshwork; just below the scleral spur; below the spur in the ciliary body; or deep posteriorly in the ciliary band.Anteriorly inserting irides, at the level of the spur or lower trabecular meshwork, may possibly be more common among Asians7,8 and in patients with hyperopia. Third, the examiner should estimate the angulation between the iris insertion and the slope of the inner cornea in the angle, in approximate steps of 10°. As discussed in Chapter 7, this systematic assessment of angle anatomy is the basis of the most detailed gonioscopic grading systems. Last, abnormalities such as neovascularization, hypoplasia, atrophy, and polycoria should be noted.

Ciliary body, iris processes, and synechiae

Beyond the final iris roll is the angle recess. At birth, this recess is incompletely developed. By the age of 1 year, the recess has formed a concavity into the anterior surface of the ciliary body. The ciliary body appears as a densely pigmented band deep to the trabecular surface. Its anterior extension merges into the scleral spur, which appears as a white line between the ciliary body and the more anterior pigmented trabecular band. If there is no pigment in the trabecular meshwork, the ciliary body will be the only pigmented structure in the angle wall. In angle recession the ciliary body may be broadly exposed. Irregular, thread-like fibers of the anterior iris stroma sometimes arborize across the angle recess and are called iris processes (see Fig. 5-5A). Gonioscopically, the processes usually seem to terminate near the spur, but some may extend in front of Schlemm’s canal, occasionally running as high as Schwalbe’s line. Larger processes represent an incomplete embryologic separation of the iris from the angle wall, which is seen in exaggerated form in the pathologic congenital syndrome of Axenfeld. Most of the fibers lose their pigment at the scleral spur and then merge with the innermost layer of the trabecular meshwork, called the uveal meshwork.

In blue eyes, the iris processes are light gray and difficult to see, but in brown eyes, the pigmented processes stand out prominently against the light background of the scleral spur.The neophyte gonioscopist may misinterpret these processes as peripheral anterior synechiae. They do not interfere in any way with outflow of aqueous humor (Fig. 5-5).

True synechiae are formed when the peripheral iris becomes attached to the trabecular wall.There are several clues for distinguishing iris processes from peripheral anterior synechiae. Iris processes are fibers or syncytial sheets that closely follow or bridge the concavity of the angle recess and that usually allow a view of the angle recess behind them unless they are extraordinarily dense. Peripheral anterior synechiae are actual adhesions of iris tissue that cover and occlude variable amounts of the angle.They can insert low at the level of the scleral spur (such as after laser trabeculoplasty) to as high as Schwalbe’s line and beyond (as with the irido-corneo-endothelial syndromes). Often normal angle structures can be seen in one area but are concealed by the synechiae in other areas. Synechiae can form only when the iris is pushed against the trabecular meshwork, as in angleclosure glaucoma, or when the iris is pulled up onto the meshwork as the result of the shrinkage of inflammatory products or fibrovascular membranes attached to both iris and meshwork. In the area of a synechia, peripheral iris tissue butts flat against the trabecular surface; it does not wrap around the angle recess as does an iris process – a distinction well appreciated during indentation gonioscopy.

Scleral spur

The most anterior projection of the sclera internally is the scleral spur. In wide-angled eyes, it is seen gonioscopically as a gray-white line of varying width at the outer end of the angle recess, and it is the point of attachment of the ciliary body and the point of termination of most of the iris processes. If blood is in Schlemm’s canal, it lies just anterior to the spur.

The spur forms the posterior concavity of the scleral sulcus. Schlemm’s canal is held in the sulcus by the corneoscleral trabecular sheets that form an inner wall to the sulcus. Most of these sheets insert at the spur. The spur is also the insertion point for most of

(A)

Schwalbe’s line

Trabecular meshwork

Schlemm’s canal

Scleral spur

Iris processes

(B)

the longitudinal muscle fibers of the ciliary body, whose action alters the facility of aqueous outflow (see Fig. 5-1).The spur’s crisp white appearance is the most helpful landmark in orienting the gonioscopist. It is also prominent in ultrasonic biomicroscopy because unlike other angle structures such as the posterior trabecular mesh-

work, it can be readily identified and thus used as an important landmark in quantifying angle measurements.31,31b

Schwalbe’s line

Another important gonioscopic landmark, Schwalbe’s line, marks the most anterior extension of the meshwork and the termination of Descemet’s membrane of the cornea. By slit-lamp examination of

normal eyes it often can be seen somewhere in the limbal circumference as a hazy zone of the inner corneal surface. With an indirect contact lens, the corneal parallelepiped of the slit-lamp beam comes together at this point (Fig. 5-6).With the use of the Koeppe contact lens (see Ch. 6 for explanation of Koeppe and Zeiss gonioscopy), Schwalbe’s line is seen as a translucent or white ledge that projects slightly into the anterior chamber,32 or it may be a vague line of demarcation between the smooth surface of Descemet’s membrane that covers the inner cornea and the less transparent rough texture of the uveal meshwork.

The line itself is composed of a bundle of collagenous connective tissue fibers running circumferentially around the eye at the end of Descemet’s membrane. Here the corneal radius of curvature