In addition to the function as assessed by such tests as Visual Fields, Visual Acuity, and colour vision, an important ancillary test for glaucoma patients or suspects is 3D imaging of the optic nerve or the surrounding nerve fiber layer. These structural tests are correlated with the functional test results to look for progression of or to glaucoma.
In our practice, we use the Heidelberg Retinal Tomogram (HRT) for 3D imaging of the optic nerve; it has a proven track record at UBC since 1994. The Ocular Coherence Topography devices (OCT) is used in other practices but is better for looking for retinal disease than for glaucoma and does not have a proven track record for looking for change over time.
Early in the disease process of glaucoma, individual nerve fibers in the eye’s optic nerve are lost, causing an associated pattern of nerve-fiber-layer thinning. This problem can later translate into loss of tissue at the optic nerve head, resulting in visual field defects and, ultimately, loss of vision.
One technique used to measure the nerve fiber layer is called scanning laser polarimetry, which utilizes a device called a GDx scanner. Another technique uses a low-power laser light and a process called optical coherence tomography (OCT). These new imaging techniques can help provide an objective measurement of the nerve fiber layer, enhancing the ability to effectively diagnose and monitor glaucoma.
Both tests are done in the ophthalmologist’s office. During these tests, the patient is required only to remain still while the image is scanned.
(c) 2009 Robert M Schertzer, MD, MEd, FRCSC with some material 2007 The American Academy of Ophthalmology
This post was written by Rob Schertzer