Continuum. The glaucoma continuum has been proposed to describe the stages. Structure and function are mentioned. Early on, structural damage to the optic nerves occur without functional vision loss. As the disease progresses, visual deficits occur.
Spectrum. It can be divided into pre-perimetric disease (before anything shows up on visual field testing), and perimetry disease (once you have visual field abnormalities), and at that point glaucoma can be divided into mild, moderate, and severe based on how abnormal the field is. Usually it's end stage when central vision is also diminished.
Ability to disting- Uish an image or object from its surrounding space is the contrast sensitivity. It is typically not measured in routine exam. Contrast sensitivity is affected by type of correction. There is a loss of contrast sensitivity at all stages of glaucoma. Some feel that the earliest loss occurs in the blue yellow spectrum. Multifocal lenses can also result in loss of contrast sensitivity.