Glaucoma causes an enlargement of the depression (or cupping) of the optic nerve head (or optic disc) where the optic nerve enters the eye. It also causes a thinning of the nerve fiber layer that radiates from the optic nerve head into the inner layer of the retina (the image-sensing layer that lines the back of the eye). These changes can be determined by eye doctors either by direct examination or with the use of specialized photography. However, a direct examination is subjective and can only provide a qualitative assessment that varies from doctor to doctor.

There are several new imaging technologies available that can measure the degree of cupping and retinal nerve fiber layer loss. Measurements derived from the images of a subject’s eye can be compared with a database of measurements from normal eyes to determine whether an individual has glaucoma. These measurements can then be tracked over time to determine whether the glaucoma is causing progressive damage. These objective and precise measurements are becoming more and more important to the management of glaucoma.

The AIG study utilizes the three most important and currently-employed glaucoma imaging technologies: optical coherence tomography (OCT), scanning laser polarimetry(SLP), and scanning laser tomography (SLT).

Optical coherence tomography produces a cross-sectional image of the eye in a manner similar to ultrasound, except that it uses light instead of sound waves and can produce a much more detailed picture. This technology is used to evaluate both the optic nerve and the retina. The high-depth resolution of OCT provides very accurate measurements of the contour of the optic nerve head, as well as of the thickness of the retinal nerve fiber layer and other retinal layers affected by glaucoma.

Scanning laser polarimetry measures how retinal nerve fibers around the optic disc affect the polarization of laser light reflected from the eye.

Scanning laser tomography measures the surface contour of the optic nerve head.