Classification

Figure 1-1 Optic disc photograph demonstrating optic disc excavation, or “cupping.” Note the focal neural rim loss (arrow) and exposed laminar pores superiorly. (Courtesy of Angelo P. Tanna, MD.)

In patients with glaucoma, the IOP at baseline—regardless of its actual level—is too high for retinal ganglion cell function and survival. It has been shown that in most patients with glaucoma, lowering the IOP will stop or slow visual field loss. In some eyes, however, optic nerve damage may progress despite treatment to lower the IOP. Clinicians often imprecisely use the word glaucoma in describing conditions in which the IOP is elevated in the absence of known glaucomatous neuropathy. Although this is common parlance, it should be avoided. Quigley HA. Glaucoma. Lancet. 2011;377(9774):1367–1377.

Classification

Open-Angle, Angle-Closure, Primary, and Secondary Glaucomas Adult forms of glaucoma are classified as open angle or angle closure and as primary or secondary (Table 1-1). Pediatric forms of glaucoma are described in Chapter 11. Distinguishing open-angle glaucoma from angle-closure disease is essential from a therapeutic standpoint. Open angle In open-angle glaucoma (OAG), no obstruction of the trabecular meshwork is visible on gonioscopic examination of the anterior chamber angle. The condition is further classified as primary open-angle glaucoma (POAG) when no underlying abnormality known to cause CHAPTER 1: Introduction to Glaucoma: Terminology, Epidemiology, and Genetics ● 7

neuropathy, it is known as angle-closure glaucoma. Angle closure is classified as primary in the absence of an underlying disorder to explain the mechanism of iridotrabecular contact or secondary when the angle closure can be attributed to certain disease processes (see Table 1-1). Globally, primary angle closure is a major public health problem. Normal aqueous humor flow in the anterior segment is illustrated in Figure 1-2A. In primary angle closure (and in some forms of secondary angle closure), the flow of aqueous humor from the posterior to the anterior chamber is obstructed at the pupil (Fig 1-2B). The resulting pressure gradient pushes the peripheral iris forward into the anterior chamber angle. This is known as pupillary block angle closure. In some forms of secondary angle closure and in plateau iris, the peripheral iris or the entire lens–iris interface is pushed forward, narrowing the iridocorneal angle (see Chap- ter 9 in this volume). This can result from an abnormality of the ciliary body, posterior segment tumors, hemorrhage, or other causes described in Chapter 10. In other forms of secondary angle closure, the peripheral iris is pulled forward, typically by contraction of a cellular, fibrovascular, or inflammatory membrane. These conditions are called non– pupillary block angle closure.

Drainage through trabecular meshwork

Schlemm canal

Episcleral vein

Uveoscleral drainage route

Ciliary body

Obstruction of drainage pathways by the iris

B Figure 1-2 Aqueous humor flow. A, Normal flow of aqueous humor from the posterior chamber, through the pupil, and into the anterior chamber. Aqueous humor exits the eye through 2 pathways in the iridocorneal angle: the trabecular meshwork and the uveoscleral pathway. B, In primary angle closure due to pupillary block, the flow of aqueous through the pupil is obstructed, resulting in a positive pressure gradient between the posterior and anterior chambers, anterior displace- ment of the peripheral iris, and closure of the anterior chamber angle. (Illustration by Mark Miller.) CHAPTER 4: Clinical Evaluation and Imaging of the Anterior Segment ● 41

Slit-Lamp Biomicroscopy

Biomicroscopy of the anterior segment is performed to detect signs of underlying ocular conditions that may be associated with glaucoma or ocular hypertension, to evaluate the eye in preparation for glaucoma surgery, and to monitor the function of a previously performed glaucoma surgery. BCSC Section 8, External Disease and Cornea, discusses slit- lamp technique and the examination of the external eye in greater depth.

Conjunctiva Eyes with acutely elevated intraocular pressure (IOP) may have conjunctival hyperemia. Long-term use of many ocular hypotensive medications may also cause conjunctival hyperemia. Allergic or hypersensitivity reactions to medications (especially a2-adrenergic agonists) or their preservatives can result in a follicular conjunctivitis. Other potential ad- verse effects of topical hypotensive drugs include decreased tear production, foreshorten- ing of the conjunctival fornices, and, in severe cases, pseudopemphigoid with conjunctival scarring. Prior to filtering surgery, the presence or absence of subconjunctival scarring or other conjunctival abnormalities is assessed. The presence or absence of any filtering bleb is noted. If a bleb is present, it is characterized as either cystic or diffuse, and its size, degree of elevation, amount of vascularization, and integrity are noted. A Seidel test is performed if a leak is suspected (Fig 4-1).

A B

C Figure 4-1 Seidel test. After application of a concentrated fluorescein solution, quenching will block fluorescence unless there is an aqueous humor leak that dilutes the fluorescein. The dark area on the right of these images represents an area of highly concentrated fluorescein. As aqueous humor leaks (arrow, A) the fluorescein is diluted, and an enlarging rivulet of fluorescence is detected (A–C). (Courtesy of Angelo P. Tanna, MD.) CHAPTER 4: Clinical Evaluation and Imaging of the Anterior Segment ● 49

A B (A) Anterior to Schwalbe’s line 10˚ (B) Behind Schwalbe’s line 20˚ 30˚ (C) Scleral spur visible 40˚ (D) Deep (iris root attaches to anterior ciliary body) (E) Extremely deep (> 1 mm of ciliary body visible)

(B) Bowing anteriorly (P) Plateau configuration (F) Flat (C) Concave

Figure 4-5 The Spaeth gonioscopic classification of the anterior chamber angle, based on 3 vari- ables: A, site of iris attachment to the inner surface of the cornea, sclera, or ciliary body; B, angu- lar width of the angle recess; C, configuration of the peripheral iris. (Illustration courtesy of Mark Miller.)

Figure 4-6 Goniophotograph showing blood in the Schlemm canal, visible through the semi- opaque trabecular meshwork. Elevated episcleral venous pressure resulted in blood reflux into the canal. (Courtesy of G.A. Cioffi, MD.)

Normal blood vessels in the angle include radial iris vessels, portions of the arterial circle of the ciliary body, and vertical branches of the anterior ciliary arteries. Normal vessels are oriented either radially along the iris or circumferentially (in a serpentine manner) in the ciliary body face. Vessels that cross the scleral spur to reach the trabecular meshwork are 260 ● Glaucoma

A B

C D Figure 13-7 Clinical photographs showing creation of a scleral flap 4 mm wide and 2.0–2.5 mm from front to back at 50%–75% scleral depth. A, Posterior margin is dissected with a fine blade. B, Crescent knife is used to dissect a partial-thickness scleral tunnel. C, Sides of the tunnel are opened to create a flap. D, Final appearance. (Courtesy of Keith Barton, MD. Reproduced with permission of Moorfields Eye Hospital.)

Fistula creation A paracentesis provides access to the anterior chamber to allow re-formation of the chamber with balanced salt solution or viscoelastic when needed. An incision into the anterior chamber is created under the scleral flap with a sharp blade. A corneoscleral block of tis- sue is removed (Fig 13-8), creating a fistula that allows aqueous to flow directly from the anterior chamber to the subconjunctival space. The fistula can be made freehand or with a trephining device such as a Kelly Descemet membrane punch. This fistula is typically cen- tered underneath the scleral flap and is small enough so that the flap overlaps it on all sides. Iridectomy An iridectomy prevents iris from occluding the fistula (Fig 13-8D). Some surgeons do not perform an iridectomy in selected patients, as it is believed the risk of fistula occlusion is low in certain pseudophakic eyes. The risks of iridectomy (bleeding, inflammation) should be weighed against the risk of fistula obstruction.