Sense of contrast (visual perception)

what is Sense of contrast:

It is the ability of the eye to perceive slight changes in the luminance between regions which are not separated by definite borders. Loss of contrast sensitivity results in mild fogginess of the vision. Contrast sensitivity is affected by various factors like age, refractive errors, glaucoma, amblyopia, diabetes, optic nerve diseases and lenticular changes. Further, contrast sensitivity may be impaired even in the presence of normal visual acuity.