Glaucoma
Edward J. Rockwood, MDa,*, Sumit Sharma, BSb, Brandy C. Hayden, BSc, Arun D. Singh, MDd
KEYWORDS
Ultrasound biomicroscope Glaucoma
Angle-closure glaucoma Pigmentary glaucoma
Glaucoma surgery Iridocorneal endothelial syndrome
Peripheral anterior synechiae Scleritis
Ultrasonic A-scan and B-scan imaging and ultrasound biomicroscopy (UBM) imaging can assist the clinician in the diagnosis and management of patients who have glaucoma. A-scan ultrasonography is used most frequently to determine ocular axial length for purposes of intraocular lens implant (IOL) calculation. Axial length usually is shorter than normal in eyes with primary angle-closure glaucoma, longer than normal in eyes with pigmentary glaucoma (associated with myopia), and may range from shorter to longer than normal in primary openangle glaucoma. Measurement of axial length with A-scan ultrasonography usually is not performed before glaucoma filtering surgery but can be helpful in ascertaining the axial length of a highly myopic eye. Alternatives to retrobulbar anesthesia may be preferred for the high-axial myopic eye to reduce the risk of inadvertent globe perforation during anesthetic administration. Similarly, B-scan ultrasonography can be used to map the location and extent of staphyloma formation to avoid accidental trauma to the globe.
B-scan ultrasonography typically is used for the diagnosis and management of ocular posterior segment and orbital diseases but is of value in the management of the patient who has glaucoma when there is little or no visualization of the posterior segment. Corneal edema, anterior chamber hyphema, or vitreous hemorrhage may be present in an eye with very high intraocular pressure.
B-scan ultrasonography is indicated to rule out the presence of a retinal detachment or intraocular tumor, either of which would require appropriate treatment in addition to glaucoma management. B-scan ultrasonography can detect significant glaucomatous optic disc cupping in patients who have glaucoma when there is no direct view of the fundus for any of a variety of reasons (Fig. 1).
UBM uses a high-frequency (35–80 MHz) transducer to image structures of the anterior segment (see the article by Simpson, elsewhere in this issue). It has high resolution but poor ocular tissue penetration. Image degradation prevents UBM imaging of more posterior ocular anatomy. UBM is ideal for the assessment of anterior chamber angle anatomy and anterior segment abnormalities in patients who have glaucoma.
ANTERIOR ANGLE EVALUATION
Relative Pupillary Block (Primary
Angle-closure Glaucoma)
High-frequency anterior segment UBM can assist the clinician in the evaluation and management of the patient who has narrow angles or angleclosure glaucoma.1,2 In the patient who has primary angle-closure glaucoma, timely management with laser peripheral iridotomy is essential for preventing visual loss.
Angle-closure glaucoma is found more commonly in the hyperopic patient who has a short ocular axial length (typically <23 mm) and often
aCleveland Clinic, Lerner College of Medicine of Case Western Reserve University, 9500 Euclid Avenue, Cleveland, OH 44195, USA
bCleveland Clinic, Lerner College of Medicine, 9500 Euclid Avenue, Cleveland, OH 44195, USA
cDiagnostic Imaging, Cole Eye Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195, USA
dDepartment of Opthalmic Oncology, Cole Eye Institute and Taussig Cancer Center, 9500 Euclid Avenue, Cleveland, OH 44195, USA
* Corresponding author. Cole Eye Institute (i-30), 9500 Euclid Avenue, Cleveland, OH 44195. E-mail address: rockwoe@ccf.org (E.J. Rockwood).
Ultrasound Clin 3 (2008) 207–215 doi:10.1016/j.cult.2008.04.008
1556-858X/08/$ – see front matter ª 2008 Elsevier Inc. All rights reserved.
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Fig.1. Optic disc cup. (A) Fundus photograph showing large optic disc cup suggestive of advanced glaucoma. (B) B-scan ultrasonography demonstrates corresponding concave bowing of the optic disc (arrows).
a large, cataractous lens. A-scan ultrasonography can confirm the presence of a short axial length and thick lens in these eyes, and in some cases frank nanophthalmos (axial length <21 mm) may be detected. Depending on the amount of angle closure in the peripheral anterior chamber angle, the intraocular pressure may be normal or elevated and often is variable. Slit-lamp examination shows a shallow peripheral anterior chamber. In this clinical setting, gonioscopy is performed on patients who have glaucoma or ocular hypertension and can help establish or rule out an angle-closure mechanism. In the clinical evaluation of the patient who has primary angle-closure or narrow-angle glaucoma, the anterior segment UBM provides cross-sectional images of the peripheral anterior chamber angle over 360 of the anterior segment. UBM results can be compared with gonioscopic findings to plan patient management.
The anterior chamber angle may be wide open, narrow without closure, or have early or advanced angle closure. A UBM performed on a normal eye shows a flat iris extending from the pupillary
margin to the iris root in the ciliary recess, just posterior to the scleral spur. In patients who have primary angle-closure glaucoma or narrow angles, the iris is not in a flat plane but is bowed anteriorly (anterior convexity) secondary to relative pupillary block. The peripheral iris is pushed forward, narrowing or closing the anterior chamber angle (Fig. 2A). Initially the closure is only appositional, but permanent synechial angle closure may occur over time. Narrow or closed angles with permanent adhesions in the angle (peripheral anterior synechiae) require laser peripheral iridotomy to eliminate relative pupillary block and halt the progression of peripheral anterior synechiae. Laser iridotomy relieves the relative pupillary block and causes the peripheral iris to become displaced more posteriorly, opening the angle (see Fig. 2B). Persistence of angle narrowing after the creation of a good, patent laser peripheral iridotomy is common. Ciliary body prominence immediately behind the peripheral iris may cause persistence of anterior chamber angle narrowing after successful laser peripheral iridotomy. This
Fig. 2. Closed angle. (A) Peripheral iridocorneal touch observed with UBM indicates that the angle is closed (arrow). (B) After peripheral iridotomy (arrowhead), the angle (arrow) has opened.
persistent narrowing is referred to as ‘‘plateau iris configuration.’’ A thicker iris may also play a role in the persistence of angle narrowing after successful laser peripheral iridotomy.3
Gonioscopic angle findings and UBM scans have been shown to be in agreement and to be dependent on the amount of ambient and slitlamp illumination.4 Best results from gonioscopy and UBM scanning for the determination of iridotrabecular apposition can be obtained by performing these examinations in a dark room. Indentation gonioscopy can be performed to establish whether angle closure is appositional or synechial.5 UBM scanning can document the response to changing from light to dark conditions6 and can be used for a dark room provocative test.7
UBM scanning has shown subclinical uveal effusion in eyes with primary angle-closure glaucoma and also in the noninvolved fellow eye.8 Uveal effusion may be a latent factor in acute primary angle-closure glaucoma and in the development of aqueous misdirection.
Complete Pupillary Block (Iris Bombe´)
Complete pupillary block (iris bombe´) is uncommon and occurs most commonly in association with uveitis or after recent ocular trauma or intraocular surgery. Active ocular inflammation may cause iris adhesion to adjacent structures. If the eye is phakic, the posterior surface of the peripupillary iris adheres to the anterior lens capsule, causing complete pupillary block (Fig. 3). Similarly, the iris may adhere to the intraocular lens in a pseudophakic eye with a posterior chamber IOL or to the vitreous face in an aphakic eye. UBM scanning can confirm this abnormality, although the diagnosis can be made at the slit lamp and seldom requires UBM scanning. In an eye with an anterior
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chamber IOL but without a prophylactic surgical peripheral iridectomy, aqueous humor can push the iris against the posterior surface of the IOL and cause pupillary block. No iris-to-IOL adhesions are required for diagnosis.
Plateau Iris Configuration
In eyes with relative pupillary block, the iris exhibits anterior convexity visible on slit-lamp examination, gonioscopy, and UBM. In eyes with plateau iris syndrome, the iris profile is straight, even after iridotomy, and the ciliary processes are located anteriorly (Fig. 4). This location prevents the peripheral iris from falling away from the trabecular meshwork after peripheral iridotomy. The distance between the trabecular meshwork and the ciliary process forms a fixed port through which the iris thickness must pass. The thicker the iris, the narrower is the angle. UBM scanning of eyes with plateau iris syndrome has confirmed the presence of anteriorly placed ciliary processes in these eyes.9
Ciliary Body Cysts
UBM may identify incidental ciliary body cysts in eyes with either open or closed angles. The visualization of one or more small to large, clear, echofree thin-walled bodies on UBM scanning indicates the presence of ciliary body cysts (Fig. 5). Some larger cysts present as a localized pushing forward of the iris, usually peripherally. Iris and ciliary body cysts seldom need treatment or long-term monitoring. A solid ciliary body lesion with diffuse internal echoes seen on UBM scanning may be suggestive of a tumor such as a ciliary body melanoma (see the article by Fu and Singh, elsewhere in this issue).
Fig. 3. Pupillary block. (A) Adherence of the posterior surface of the peripupillary iris to the anterior lens capsule causes pupillary block (arrows). (B) The peripheral iris is pushed forward closing the anterior chamber angle (arrow).
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Fig. 4. Plateau iris configuration. (A) The iris approach toward the anterior chamber angle is flat, and the angle is closed (white arrow). Note anteriorly placed ciliary processes (black arrow). (B) Even after the peripheral iridotomy (arrowhead), ciliary processes prevent the peripheral iris from falling away from the trabecular meshwork (arrow).
Pigmentary Glaucoma
Pigmentary or pigment-dispersion glaucoma usually is found in young, myopic patients and has some male gender predominance. Patients typically have radial peripheral iris
transillumination defects and evidence of pigmentation dispersion on slit-lamp examination. Pigment may accumulate on the corneal endothelial surface diffusely or, more characteristically, in the form of a fine, vertically oriented lower central corneal endothelial line referred to as
Fig. 5. Iris pigment epithelial cyst. (A) Anterior segment photograph with a broad beam reveals normal iris appearance. (B) With a slit beam, anterior bulging of the iris becomes evident. (C) Note echo-free, thin-walled cyst on UBM (arrows).