eMedicine Specialties > Ophthalmology > Intraocular Pressure

Glaucoma, Complications and Management of Glaucoma Filtering: Workup

Author: Antonio Pascotto, MD, Consulting Ophthalmologist, Pascotto, Istituto per la Salute degli Occhi, Clinica Mediterranea, Italy
Coauthor(s): Sergio Claudio Saccà, PhD, Professor of Ophthalmology, Department of Neurological and Visual Sciences, Ospedale San Martino, Italy; Mauro Fioretto, MD, Professor of Ophthalmology, University Eye Clinic of Genova; Head of Ophthalmology Department, Hospital of Casale Monferrato, Italy; Vincenzo Orfeo, MD, Head, Operating Unit, Clinica Mediterranea, Naples, Italy
Contributor Information and Disclosures

Updated: Nov 1, 2006

Workup

Imaging Studies

• 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 procedure is similar to ultrasonographic procedures involving the heart (eg, echocardiography) or the examination of a baby before birth. 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 (see Media file 7) and pigment dispersion syndrome are the 2 forms of glaucoma that have primarily benefited from UBM research.
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    Pupillary block angle-closure glaucoma. Courtesy of the Ocular Imaging Center, New York Eye and Ear Infirmary.

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

• OCT is a noninvasive, noncontact technology. This exciting 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 disorders affecting the posterior pole.
  • OCT represents a radically new method for diagnostic imaging, as it enables clinicopathologic 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 structure, 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, such as magnetic resonance. OCT, which uses light, may be compared with ultrasonography, which uses 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 patients. In addition to multiple acquisition modes, this device also provides several image assessment methods.
• 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 (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.
• 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 more 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 decision regarding treatment for each patient.

Other Tests

• IOP readings
• Observation of the optic nerve
• Visual field tests (to evaluate optic nerve function)

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 used all 3 procedures as part of an overall eye examination.
  • The procedures are simple, relatively quick, and virtually painless.
• Tonometry involves the use of a tonometer that measures eye pressure (ie, IOP).
  • 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 measure IOP.
  • During air tonometry, a puff of air is sent onto the cornea to measure the pressure. No anesthetic eye drops are needed.
• The visual field test enables the ophthalmologist to determine any loss of peripheral vision.
  • 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.
• During ophthalmoscopy, an ophthalmoscope is used to look directly through the pupil at the optic nerve. Its color and appearance can indicate the presence of and the extent of damage from glaucoma.

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, as outlined below, follows the progression of glaucoma from before diagnosis to end-stage disease. This system allows ophthalmologists to stage patients' disease by using their historical chart data. These stages are as follows:

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

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