Complications and Management of Glaucoma Filtering Workup

Updated: Jan 09, 2017
  • Author: Nicholas A Moore, MD; Chief Editor: Hampton Roy, Sr, MD  more...
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Workup

Imaging Studies

Ultrasound biomicroscopy

Ultrasound biomicroscopy (UBM) is a method of imaging the eye at microscopic resolution.

UBM can be used to image any ocular disorder that falls within the penetration limits of sound at high frequencies. UBM achieves a high resolution of 50 mm by using high-frequency ultrasound transducers.

UBM is especially useful for assessing glaucoma entities with a structural component to their etiology, such as pupillary block, plateau iris syndrome, direct iris rotation, anterior synechiae, supraciliary effusions, malignant glaucoma, cystic angle closure, and pigmentary glaucoma.

The ultrasound probe is moved slowly over the surface of the eye, and images are recorded.

Structures that can be seen in a healthy eye are the cornea, the anterior chamber, the iris, the posterior chamber, the ciliary body, the sclera, the anterior lens capsule, the end of the Descemet membrane (Schwalbe line), and the scleral spur.

Angle-closure glaucoma and pigment dispersion syndrome are the 2 forms of glaucoma that have primarily benefited from UBM research. Pupillary block angle-closure glaucoma is shown in the image below.

Pupillary block angle-closure glaucoma. Courtesy o Pupillary block angle-closure glaucoma. Courtesy of the Ocular Imaging Center, New York Eye and Ear Infirmary.

Optical coherence tomography

Optical coherence tomography (OCT) is a noninvasive, noncontact technology. This technology has revolutionized the early detection of glaucoma through its ability to evaluate the nerve cells damaged in glaucoma.

OCT was introduced to eye care on the heels of other technologies that assist in the diagnosis and management of glaucoma. Although previous technology to measure the thickness of the retinal nerve fiber layer was exceptional, they had limitations and did not readily provide access for assessing the rest of the posterior pole. OCT was designed for the diagnosis and intervention of glaucoma, but clinicians soon realized its utility in diagnosing and managing other conditions of the head of the optic nerve and in providing tremendous insight into retinal diseases.

OCT represents a radically new method for diagnostic imaging, as it enables clinical tomographic imaging of the microstructure of the ocular tissue by measuring the echo time delay and intensity of back-scattered light. OCT allows for real-time evaluation of retinal and optic nerve structures, and the evolving technology is equally applicable to tissues of the anterior segment. The images have a resolution of 1-15 µm, which is better than that of other standard imaging techniques. OCT, which uses light interference patterns, may be compared with ultrasonography, which uses the reflection of sound waves.

The currently available Stratus OCT3 device allows for both optic nerve and retinal imaging with multiple acquisition modes, including rapid acquisition and more time-consuming algorithms. The rapid acquisition modes sacrifice resolution for speed, but often this tradeoff is desirable in uncooperative or inattentive patients. In addition to multiple acquisition modes, this device also provides several image assessment methods.

Heidelberg retina tomography

The Heidelberg retina tomograph (HRT) is a confocal laser-scanning microscope for acquiring and analyzing 3-dimensional images of the posterior segment.

The HRT enables quantitative assessment of the retinal topography and precise follow-up of the topographic changes.

The most important routine clinical application of the HRT is the topographic description and the follow-up of the glaucomatous optic nerve head.

Scanning laser polarimetry

Scanning laser polarimetry (SLP) makes a quantitative measurement of the retinal nerve fiber layer, which cannot be easily assessed via other clinical methods.

SLP measures the retinal nerve fiber layer directly, regardless of the anatomy of the cup.

With a reproducibility of less than 8 µm, SLP is sensitive to detecting any changes.

Polarimetry and thickness measurements do not use a reference plane and are not affected by refractive error. [5]

GDx nerve fiber analyzer

The GDx nerve fiber analyzer is a type of scanning laser polarimeter. The GDx device uses a diode laser in the near infrared region to measure 65,536 retinal points and the thickness of the nerve fiber layer. The axons in this layer have a birefringent property that causes the polarized light passing through it to undergo a phase shift. The amount of phase shift is directly proportional to the thickness of the nerve fiber layer.

The procedure is performed in an undilated pupil. Three images are obtained in each eye, and the images are then averaged for a baseline reading. The GDx device comes with computer software that allows the physician to interpret the results, comparing them with findings in normal eyes.

This test provides the physician with quantitative information and is a useful adjunct along with visual field testing (which is user dependent). The GDx test also provides important information that is useful in monitoring the status of the optic nerve over years.

Alone, results of the GDx test do not confirm the diagnosis of glaucoma; therefore, the physician must use all of the baseline and follow-up data to make a decisions regarding treatment for each patient.

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Other Tests

Other tests are as follows:

  • Intraocular pressure (IOP) readings
  • Slit lamp examination of the optic nerve
  • Visual field tests (to evaluate optic nerve function)
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Diagnostic Procedures

Three common diagnostic procedures, tonometry, visual field tests, and ophthalmoscopy, enable ophthalmologists to screen patients for glaucoma. To make a definitive diagnosis, ophthalmologists often use all 3 procedures as part of an overall eye examination. The procedures are simple, relatively quick, and virtually painless.

Tonometry

Tonometry involves the use of a tonometer that measures intraocular eye pressure

​During tonometry, the eye is anesthetized with drops, and while the patient is examined with a slit lamp, a plastic prism is lightly pushed against the eye to estimate the IOP.

During air tonometry, a puff of air is sent onto the cornea to measure the pressure. No anesthetic eye drops are needed.

It is important to record the central corneal thickness using a pachymeter, as corneas that are too thick or too thin can affect the IOP readings, thereby giving falsely low or high IOP measurements.

Visual field test

The visual field test enables the ophthalmologist to determine any patterns of vision loss.

The patient places his or her chin on a stand placed in front of a computer screen. When a flash of light appears, the patient is asked to press a button.

A computerized printout provides an accurate assessment of the patient's peripheral vision.

It is important to check the reliability of each individual's visual field assessment, as poor testing can complicate analysis of glaucoma progression.

Ophthalmoscopy

During ophthalmoscopy, an ophthalmoscope is used to look directly through the pupil at the optic nerve. The color and appearance of the optic nerve head can indicate the presence of and the extent of damage from glaucoma.

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Staging

Staging of glaucoma is important because it helps to establish target pressures and to determine the frequency of patient follow-up examinations. The modified glaucoma staging system follows the progression of glaucoma from before diagnosis to end-stage disease based on visual field findings. This system allows ophthalmologists to stage patients' disease by using each patient’s individualized data. These stages are as follows:

  • 0 - Normal
  • 1 - Early
  • 2 - Moderate
  • 3 - Advanced
  • 4 - Severe
  • 5 - End stage
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