GDx Polarimetry

Eqiupment:

• Laser Diagnostics GDx Polarimeter

Procedures:

• Retinal Nerve Fibre Layer Thickness Measurement
• Comparison With Normal Database
• Progression Analysis

Scanning Laser Polarimetry is a fast, non-contact method for making accurate measurements of the nerve fibre layer thickness. At LEDC, we are now able to provide this form of testing using the GDx VCC machine by Laser Diagnostic Technologies. The patient looks at a fixation light inside the machine as it scans the back of the eye. The results of the test are clearly displayed on the report showing the deviation from normal at each location on the image. Follow-up reports may be produced which show changes in the amount of nerve fibre with time. These are colour coded in a similar fashion and make it easy to identify progressing damage.

The GDx machine makes use of an optical property of the nerve fibre known as 'birefingence'. This is the ability of a material to rotate the polarisation of a beam of light. The machine shines a light into the eye which is reflected off the fundus. This passes through the nerve fibre layer before being reflected back to a detector in the machine. By measuring the amount by which the polarisation of the reflected light has rotated, the machine can determine how much nerve fibre the light has passed though.