What is reduced contrast sensitivity in vision & at what stage in open angle glaucoma can it occur?

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.