Johns Hopkins Health Alert
A Look at New Technologies to Identify Early-Stage Glaucoma
For decades, doctors viewed open-angle glaucoma as a slowly progressive disease that meaningfully affected vision only in the later stages. But glaucoma damage begins well before conventional tests can identify it, before you're consciously aware of it, and before it impacts your ability to perform day-to-day functions like reading, walking, and driving. The goal is to identify people at greatest risk for disease progression to initiate early, aggressive treatment.
Efforts to more accurately identify early-stage glaucoma have focused on imaging studies that can identify structural changes in the optic nerve head and nerve fiber.
Identifying structural changes. Traditionally, eye doctors have looked into your eye to assess whether you have structural damage to the optic nerve (a process called ophthalmoscopy). On examination, the head of the nerve looks a bit like a saucer, with a shallow central depression, or "cup." Normally, most of the optic nerve head is filled with axons exiting the eye towards the brain. However, glaucoma can cause these axons to die, producing a characteristic appearance in which the central cup becomes very deep and very wide. At this point, doctors may suspect the presence of glaucoma.
To make a definitive glaucoma diagnosis, the doctor must correlate these findings with the presence of visual field loss or the loss of ganglion cell axons as they travel towards the optic nerve head.
Today, more sophisticated tests can identify these structural changes before they are evident on ophthalmoscopic examination.
- Scanning laser polarimetry for glaucoma. This test uses laser light to measure the thickness of the nerve fiber layer. This type of analysis is important because nerve fiber layer abnormalities are frequently seen in people with early glaucoma even though their standard perimetry test results are normal. In fact, findings from evaluations of the nerve fiber layer can predict future vision loss years before reading, driving, night vision, or motion detection are affected.
- Ocular coherence tomography for glaucoma. This technology uses infrared light to create a detailed cross-sectional view of the retina. Damage from glaucoma results in loss of ganglion cells and ganglion cell axons, which results in a thinner retina, particularly in damaged areas.
- Confocal scanning laser ophthalmoscopy for glaucoma. With this technique, the doctor uses a special laser microscope to scan the retinal surface and optic nerve. The device then creates a three-dimensional image of the optic nerve, including an outline of the optic cup, and measures the parameters.
- Optic nerve head analyzer for glaucoma. Known as the Glaucoma-Scope, this device collects data from the eye to determine the exact ratio of the optic disc to its cup. It also monitors changes to the structure of the optic disc and can measure its rim.
Posted in Vision on August 27, 2010
Medical Disclaimer: This information is not intended to substitute for the advice of a physician. Click here for additional information: Johns Hopkins Health Alerts Disclaimer
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