Pick a Team.(Brief Article)

GDx: Early diagnosis is the key.

The GDx is a powerful diagnostic tool that can help us evaluate the glaucoma suspects we see every day in clinical practice. In many cases, it's not enough for us to perform visual fields and optic nerve evaluation with ophthalmoscopy and tonometry. We need more information.

How It Works

The GDx is a scanning laser polarimetry device made by Laser Diagnostic Technologies (LDT) of San Diego. It gives you a direct measurement of the retinal nerve fiber layer (RNFL). The technique utilizes the birefringent properties of the nerve fibers that arise from their parallel anatomical organization. When a laser scanning beam of polarized light makes a double pass through the tissue, there is a change to the polarized state of the light. The change in polarization, referred to as retardation, is related to the thickness of the RNFL on a linear basis. This is how we get a measurement.

To obtain its data, the GDx measures 65,500-plus data points from a 15-degree field of view around the optic nerve head. It then places an ellipse that's 1.75x larger than the outer disc margin over the image scan. From this ellipse, the GDx obtains additional information from each of the four quadrants around the optic nerve. It presents the data in several charts and plots on the color printout. You can review GDx thickness maps, TSNIT (temporal, superior, nasal, inferior, temporal) curves and numerical data to determine the overall health and integrity of the RNFL. Finally, the GDx also provides a single value, known as "The Number," which indicates the likelihood that glaucoma is present.