What does functional testing tell us about optic nerve damage?

Information from different regions of the visual field travels through specific bundles of retinal ganglion cell axons. This visual information is disrupted in patients with glaucoma, and the effects can be seen in measurements of the visual field and optic nerve. Typical shapes and sizes of glaucomatous field defects result from damage to these nerve fiber bundles at the level of the optic disk, and we have identified specific patterns of progression. These patterns apply to the visual function-specific field tests that are designed to indirectly assess sub-populations of retinal ganglion cells. The rationale for these tests is described. An argument for the importance of using visual function techniques to assess progression in an individual patient is given.